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From: John Bashinski <jbash@CISCO.COM.>
Subject: Cisco IOS password encryption facts
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X-PMFLAGS: 33554560 0
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A non-Cisco source has recently released a new program to decrypt user
passwords (and other passwords) in Cisco configuration files. The program
will not decrypt passwords set with the "enable secret" command.
The unexpected concern that this program has caused among Cisco customers
has led us to suspect that many customers are relying on Cisco password
encryption for more security than it was designed to provide. This document
explains the security model behind Cisco password encryption, and the
security limitations of that encryption.
User Passwords
- --------------
User passwords and most other passwords (*not* enable secrets) in Cisco IOS
configuration files are encrypted using a scheme that's very weak by modern
cryptographic standards.
Although Cisco does not distribute a decryption program, at least two
different decryption programs for Cisco IOS passwords are available to the
public on the Internet; the first public release of such a program of which
Cisco is aware was in early 1995. We would expect any amateur cryptographer
to be able to create a new program with no more than a few hours' work.
The scheme used by IOS for user passwords was never intended to resist a
determined, intelligent attack; it was designed to avoid casual
"over-the-shoulder" password theft. The threat model was someone reading a
password from an administrator's screen. The scheme was never supposed to
protect against someone conducting a determined analysis of the
configuration file.
Because of the weak encryption algorithm, it has always been Cisco's
position that customers should treat any configuration file containing
passwords as sensitive information, the same way they would treat a
cleartext list of passwords.
Enable Secret Passwords
- -----------------------
Enable secrets are hashed using the MD5 algorithm. As far as anyone at
Cisco knows, it is impossible to recover an enable secret based on the
contents of a configuration file (other than by obvious dictionary
attacks).
Note that this applies only to passwords set with "enable secret", *not*
to passwords set with "enable password". Indeed, the strength of the
encryption used is the only significant difference between the two
commands.
Other Passwords
- ---------------
Almost all passwords and other authentication strings in Cisco IOS
configuration files are encrypted using the weak, reversible scheme used
for user passwords. To determine which scheme has been used to encrypt a
specific password, check the digit preceding the encrypted string in the
configuration file. If that digit is a 7, the password has been encrypted
using the weak algorithm. If the digit is a 5, the password has been hashed
using the stronger MD5 algorithm.
For example, in the configuration command
enable secret 5 $1$iUjJ$cDZ03KKGh7mHfX2RSbDqP.
The enable secret has been hashed with MD5, whereas in the command
username jbash password 7 07362E590E1B1C041B1E124C0A2F2E206832752E1A01134D
The password has been encrypted using the weak reversible algorithm.
Can the algorithm be changed?
- -----------------------------
Cisco has no immediate plans to support a stronger encryption algorithm for
IOS user passwords. Should Cisco decide to introduce such a feature in the
future, that feature will definitely impose an additional ongoing
administrative burden on users who choose to take advantage of it.
It is not, in the general case, possible to switch user passwords over to
the MD5-based algorithm used for enable secrets, because MD5 is a one-way
hash, and the password can't be recovered from the encrypted data at all.
In order to support certain authentication protocols (notably CHAP), the
system needs access to the clear text of user passwords, and therefore must
store them using a reversible algorithm.
Key management issues would make it a nontrivial task to switch over to a
stronger reversible algorithm, such as DES. Although it would be easy to
modify IOS to use DES to encrypt passwords, there would be no security
advantage in doing so if all IOS systems used the same DES key. If
different keys were used by different systems, an administrative burden
would be introduced for all IOS network administrators, and portability of
configuration files between systems would be damaged. Customer demand
for stronger reversible password encryption has been small.
November 10, 1997
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From: ice9 <ice9@PARANOIA.COM.>
Subject: Re: Cisco IOS password encryption facts
To: [email protected]
In-Reply-To: <19971111003936.1179.qmail@susan.cisco.com.> from "John Bashinski"
at Nov 10, 97 04:39:36 pm
Status:
X-PMFLAGS: 34078848 0
This is why, if you are worried about security, perhaps TACACS+ would be a good option. Even if the router can't reach the TACACS server, with proper configuration, you will still need the enable passwd just to enter maintenance mode...
And I would hope that would be configured using enable-secret.
But even if you were using level 7 encryption for your maint passwd, a maintenance mode user is rather limited in what he can do...
>
> -----BEGIN PGP SIGNED MESSAGE-----
>
> A non-Cisco source has recently released a new program to decrypt user
> passwords (and other passwords) in Cisco configuration files. The program
> will not decrypt passwords set with the "enable secret" command.
>
> The unexpected concern that this program has caused among Cisco customers
> has led us to suspect that many customers are relying on Cisco password
> encryption for more security than it was designed to provide. This document
> explains the security model behind Cisco password encryption, and the
> security limitations of that encryption.
>
> User Passwords
> - --------------
> User passwords and most other passwords (*not* enable secrets) in Cisco IOS
> configuration files are encrypted using a scheme that's very weak by modern
> cryptographic standards.
>
> Although Cisco does not distribute a decryption program, at least two
> different decryption programs for Cisco IOS passwords are available to the
> public on the Internet; the first public release of such a program of which
> Cisco is aware was in early 1995. We would expect any amateur cryptographer
> to be able to create a new program with no more than a few hours' work.
>
> The scheme used by IOS for user passwords was never intended to resist a
> determined, intelligent attack; it was designed to avoid casual
> "over-the-shoulder" password theft. The threat model was someone reading a
> password from an administrator's screen. The scheme was never supposed to
> protect against someone conducting a determined analysis of the
> configuration file.
>
> Because of the weak encryption algorithm, it has always been Cisco's
> position that customers should treat any configuration file containing
> passwords as sensitive information, the same way they would treat a
> cleartext list of passwords.
>
> Enable Secret Passwords
> - -----------------------
> Enable secrets are hashed using the MD5 algorithm. As far as anyone at
> Cisco knows, it is impossible to recover an enable secret based on the
> contents of a configuration file (other than by obvious dictionary
> attacks).
>
> Note that this applies only to passwords set with "enable secret", *not*
> to passwords set with "enable password". Indeed, the strength of the
> encryption used is the only significant difference between the two
> commands.
>
> Other Passwords
> - ---------------
> Almost all passwords and other authentication strings in Cisco IOS
> configuration files are encrypted using the weak, reversible scheme used
> for user passwords. To determine which scheme has been used to encrypt a
> specific password, check the digit preceding the encrypted string in the
> configuration file. If that digit is a 7, the password has been encrypted
> using the weak algorithm. If the digit is a 5, the password has been hashed
> using the stronger MD5 algorithm.
>
> For example, in the configuration command
>
> enable secret 5 $1$iUjJ$cDZ03KKGh7mHfX2RSbDqP.
>
> The enable secret has been hashed with MD5, whereas in the command
>
> username jbash password 7 07362E590E1B1C041B1E124C0A2F2E206832752E1A01134D
>
> The password has been encrypted using the weak reversible algorithm.
>
> Can the algorithm be changed?
> - -----------------------------
> Cisco has no immediate plans to support a stronger encryption algorithm for
> IOS user passwords. Should Cisco decide to introduce such a feature in the
> future, that feature will definitely impose an additional ongoing
> administrative burden on users who choose to take advantage of it.
>
> It is not, in the general case, possible to switch user passwords over to
> the MD5-based algorithm used for enable secrets, because MD5 is a one-way
> hash, and the password can't be recovered from the encrypted data at all.
> In order to support certain authentication protocols (notably CHAP), the
> system needs access to the clear text of user passwords, and therefore must
> store them using a reversible algorithm.
>
> Key management issues would make it a nontrivial task to switch over to a
> stronger reversible algorithm, such as DES. Although it would be easy to
> modify IOS to use DES to encrypt passwords, there would be no security
> advantage in doing so if all IOS systems used the same DES key. If
> different keys were used by different systems, an administrative burden
> would be introduced for all IOS network administrators, and portability of
> configuration files between systems would be damaged. Customer demand
> for stronger reversible password encryption has been small.
>
> November 10, 1997
>
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--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
[email protected]http://www.paranoia.com/~ice9
My opinion may not reflect that of any living person, but its the
only one that counts!!
main() {for(;;fork());}
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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Date: Tue, 11 Nov 1997 12:27:07 +0100
Reply-To: Janos Zsako <zsako@banknet.net.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: Janos Zsako <zsako@banknet.net.>
Subject: Re: cisco passwords
X-To: [email protected]
To: [email protected]
Status:
X-PMFLAGS: 33554560 0
> From [email protected] Sun Nov 2 02:09:47 1997
> From: Jared Mauch <jared@puck.nether.net.>
> I've done a few code cleanups on the decryption stuff and put
> it up for ftp with these fixes.. i have a few more to make
> so it'll just grab it from bgp sessions, ospf keys, etc..
>
> Get it from ftp://puck.nether.net/pub/jared/decrypt.c
It does not work reliably for passwords longer than eight characters.
The problem is that Cisco passwords can be 11 character long, and if the
initial seed is larger than 10, the translation table is too short.
The full translation table is as follows:
char xlat[] = {
0x64, 0x73, 0x66, 0x64, 0x3b, 0x6b, 0x66, 0x6f,
0x41, 0x2c, 0x2e, 0x69, 0x79, 0x65, 0x77, 0x72,
0x6b, 0x6c, 0x64, 0x4a, 0x4b, 0x44, 0x48, 0x53 , 0x55, 0x42
};
This copes also with the case when the passwords that are 11 character long and
the seed is 15.
Janos Zsako
PS. The passwords longer than 11 characters are allowed, however they are
truncated to the first 11 characters (just as they are to 8 in most Unix
implementations).
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Date: Wed, 12 Nov 1997 14:13:49 +1300
Reply-To: "J. Sean Connell" <ankh@canuck.gen.nz.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: "J. Sean Connell" <ankh@canuck.gen.nz.>
Subject: Re: Cisco IOS password encryption facts
To: [email protected]
In-Reply-To: <199711111037.EAA12696@primus.paranoia.com.>
Status:
X-PMFLAGS: 34078848 0
On Tue, 11 Nov 1997, ice9 wrote:
> This is why, if you are worried about security, perhaps TACACS+ would be
> a good option. Even if the router can't reach the TACACS server, with
> proper configuration, you will still need the enable passwd just to enter
> maintenance mode...
Not necessarily. If you use TACACS+ for AAA and enable AAA accounting,
you will (at least in my humble experience) be unable to get in - the cisco
must send an accounting record to the TACACS+ server, but it can't reach
the TACACS+ server, so it refuses to let you in. (If anyone knows how to
get around this without turning off aaa accounting, *please* let me know! =)
(Also note that I may have any and/or all of the above wrong - it's so long
that I can't quite remember all the exact details...)
--
J. S. Connell | Systems Adminstrator, ICONZ. Any opinions stated above
[email protected] | are not my employers', not my boyfriends', my God's, my
[email protected] | friends', and probably not even my own.
-------------------+---------------------------------------------------------
PGP key at http://www.canuck.gen.nz/~ankh/pgpkey.html
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Message-Id: <Pine.BSF.3.95q.971113194336.17453B-100000@natverket.natverket.com.>
Date: Thu, 13 Nov 1997 19:58:15 +0100
Reply-To: Michael Degerman <mide@natverket.com.>
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From: Michael Degerman <mide@natverket.com.>
Subject: Re: Cisco IOS password encryption facts
X-To: "J. Sean Connell" <ankh@canuck.gen.nz.>
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Status:
X-PMFLAGS: 34078848 0
> Not necessarily. If you use TACACS+ for AAA and enable AAA accounting,
> you will (at least in my humble experience) be unable to get in - the cisco
> must send an accounting record to the TACACS+ server, but it can't reach
> the TACACS+ server, so it refuses to let you in. (If anyone knows how to
> get around this without turning off aaa accounting, *please* let me know! =)
If you don't put a "login" line on the vty's in the Cisco box then you
will have problems, like the senario you just describe. But if you put
a "login" line on the vty's the Cisco will start with the tacacs+ login
prompt and then after trying to get a respons from the tacacs+ it will
time-out and give you a default login..
It's also depending on how you implement the tacacs+ login which
password you have as backup.. Some times you got too have a password
defined on the vty's as well because it's the default setting if noting
else is specified.
>
> (Also note that I may have any and/or all of the above wrong - it's so long
> that I can't quite remember all the exact details...)
Hey! It might be easy to learn but it's a lot easier to forget!
//Michael Degerman
------------------------------------------------------------------------
A lonely guy with a lot on the mind!
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From: Rafi Sadowsky <rafi@tavor.openu.ac.il.>
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Subject: BoS: Cisco IOS password encryption facts (fwd)
Status:
X-PMFLAGS: 34078848 0
---------- Forwarded message ----------
Date: Mon, 10 Nov 1997 16:39:36 -0800
From: John Bashinski <jbash@CISCO.COM.>
Subject: Cisco IOS password encryption facts
-----BEGIN PGP SIGNED MESSAGE-----
A non-Cisco source has recently released a new program to decrypt user
passwords (and other passwords) in Cisco configuration files. The program
will not decrypt passwords set with the "enable secret" command.
The unexpected concern that this program has caused among Cisco customers
has led us to suspect that many customers are relying on Cisco password
encryption for more security than it was designed to provide. This document
explains the security model behind Cisco password encryption, and the
security limitations of that encryption.
User Passwords
- --------------
User passwords and most other passwords (*not* enable secrets) in Cisco IOS
configuration files are encrypted using a scheme that's very weak by modern
cryptographic standards.
Although Cisco does not distribute a decryption program, at least two
different decryption programs for Cisco IOS passwords are available to the
public on the Internet; the first public release of such a program of which
Cisco is aware was in early 1995. We would expect any amateur cryptographer
to be able to create a new program with no more than a few hours' work.
The scheme used by IOS for user passwords was never intended to resist a
determined, intelligent attack; it was designed to avoid casual
"over-the-shoulder" password theft. The threat model was someone reading a
password from an administrator's screen. The scheme was never supposed to
protect against someone conducting a determined analysis of the
configuration file.
Because of the weak encryption algorithm, it has always been Cisco's
position that customers should treat any configuration file containing
passwords as sensitive information, the same way they would treat a
cleartext list of passwords.
Enable Secret Passwords
- -----------------------
Enable secrets are hashed using the MD5 algorithm. As far as anyone at
Cisco knows, it is impossible to recover an enable secret based on the
contents of a configuration file (other than by obvious dictionary
attacks).
Note that this applies only to passwords set with "enable secret", *not*
to passwords set with "enable password". Indeed, the strength of the
encryption used is the only significant difference between the two
commands.
Other Passwords
- ---------------
Almost all passwords and other authentication strings in Cisco IOS
configuration files are encrypted using the weak, reversible scheme used
for user passwords. To determine which scheme has been used to encrypt a
specific password, check the digit preceding the encrypted string in the
configuration file. If that digit is a 7, the password has been encrypted
using the weak algorithm. If the digit is a 5, the password has been hashed
using the stronger MD5 algorithm.
For example, in the configuration command
enable secret 5 $1$iUjJ$cDZ03KKGh7mHfX2RSbDqP.
The enable secret has been hashed with MD5, whereas in the command
username jbash password 7 07362E590E1B1C041B1E124C0A2F2E206832752E1A01134D
The password has been encrypted using the weak reversible algorithm.
Can the algorithm be changed?
- -----------------------------
Cisco has no immediate plans to support a stronger encryption algorithm for
IOS user passwords. Should Cisco decide to introduce such a feature in the
future, that feature will definitely impose an additional ongoing
administrative burden on users who choose to take advantage of it.
It is not, in the general case, possible to switch user passwords over to
the MD5-based algorithm used for enable secrets, because MD5 is a one-way
hash, and the password can't be recovered from the encrypted data at all.
In order to support certain authentication protocols (notably CHAP), the
system needs access to the clear text of user passwords, and therefore must
store them using a reversible algorithm.
Key management issues would make it a nontrivial task to switch over to a
stronger reversible algorithm, such as DES. Although it would be easy to
modify IOS to use DES to encrypt passwords, there would be no security
advantage in doing so if all IOS systems used the same DES key. If
different keys were used by different systems, an administrative burden
would be introduced for all IOS network administrators, and portability of
configuration files between systems would be damaged. Customer demand
for stronger reversible password encryption has been small.
November 10, 1997
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Date: Mon, 10 Nov 1997 16:39:36 -0800
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Subject: BoS: Cisco IOS password encryption facts
Status:
X-PMFLAGS: 33554560 0
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A non-Cisco source has recently released a new program to decrypt user
passwords (and other passwords) in Cisco configuration files. The program
will not decrypt passwords set with the "enable secret" command.
The unexpected concern that this program has caused among Cisco customers
has led us to suspect that many customers are relying on Cisco password
encryption for more security than it was designed to provide. This document
explains the security model behind Cisco password encryption, and the
security limitations of that encryption.
User Passwords
- --------------
User passwords and most other passwords (*not* enable secrets) in Cisco IOS
configuration files are encrypted using a scheme that's very weak by modern
cryptographic standards.
Although Cisco does not distribute a decryption program, at least two
different decryption programs for Cisco IOS passwords are available to the
public on the Internet; the first public release of such a program of which
Cisco is aware was in early 1995. We would expect any amateur cryptographer
to be able to create a new program with no more than a few hours' work.
The scheme used by IOS for user passwords was never intended to resist a
determined, intelligent attack; it was designed to avoid casual
"over-the-shoulder" password theft. The threat model was someone reading a
password from an administrator's screen. The scheme was never supposed to
protect against someone conducting a determined analysis of the
configuration file.
Because of the weak encryption algorithm, it has always been Cisco's
position that customers should treat any configuration file containing
passwords as sensitive information, the same way they would treat a
cleartext list of passwords.
Enable Secret Passwords
- -----------------------
Enable secrets are hashed using the MD5 algorithm. As far as anyone at
Cisco knows, it is impossible to recover an enable secret based on the
contents of a configuration file (other than by obvious dictionary
attacks).
Note that this applies only to passwords set with "enable secret", *not*
to passwords set with "enable password". Indeed, the strength of the
encryption used is the only significant difference between the two
commands.
Other Passwords
- ---------------
Almost all passwords and other authentication strings in Cisco IOS
configuration files are encrypted using the weak, reversible scheme used
for user passwords. To determine which scheme has been used to encrypt a
specific password, check the digit preceding the encrypted string in the
configuration file. If that digit is a 7, the password has been encrypted
using the weak algorithm. If the digit is a 5, the password has been hashed
using the stronger MD5 algorithm.
For example, in the configuration command
enable secret 5 $1$iUjJ$cDZ03KKGh7mHfX2RSbDqP.
The enable secret has been hashed with MD5, whereas in the command
username jbash password 7 07362E590E1B1C041B1E124C0A2F2E206832752E1A01134D
The password has been encrypted using the weak reversible algorithm.
Can the algorithm be changed?
- -----------------------------
Cisco has no immediate plans to support a stronger encryption algorithm for
IOS user passwords. Should Cisco decide to introduce such a feature in the
future, that feature will definitely impose an additional ongoing
administrative burden on users who choose to take advantage of it.
It is not, in the general case, possible to switch user passwords over to
the MD5-based algorithm used for enable secrets, because MD5 is a one-way
hash, and the password can't be recovered from the encrypted data at all.
In order to support certain authentication protocols (notably CHAP), the
system needs access to the clear text of user passwords, and therefore must
store them using a reversible algorithm.
Key management issues would make it a nontrivial task to switch over to a
stronger reversible algorithm, such as DES. Although it would be easy to
modify IOS to use DES to encrypt passwords, there would be no security
advantage in doing so if all IOS systems used the same DES key. If
different keys were used by different systems, an administrative burden
would be introduced for all IOS network administrators, and portability of
configuration files between systems would be damaged. Customer demand
for stronger reversible password encryption has been small.
November 10, 1997
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Subject: CORRECTED Preliminary Notice: Cisco LocalDirector enable password
loss
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X-Cc: [email protected]
To: [email protected]
Status:
X-PMFLAGS: 33554560 0
The version I just sent out was a draft; I sent it by mistake. It contains
no factual errors that I know of, but differs slightly in its
recommendations and administrative information. Please use the attached
version instead.
-- John B.
-----BEGIN PGP SIGNED MESSAGE-----
Preliminary Notice:
Cisco LocalDirector Enable Password Loss
November 16, 1997, 09:00 AM US/Pacific, Revision 2
- ------------------------------------------------------------------------
This is a preliminary notice describing a security problem about which there
has been customer concern. Cisco does not yet have full information about
this problem. Customers should use great caution in relying on the
information in this notice.
Summary
At least two customers have reported failures in the enable password
mechanism in version 1.6.3 of Cisco's LocalDirector product. Affected
systems allow users to enter privileged mode without providing the correct
enable password; any string will suffice as a password. This applies only to
the privileged-mode enable password; the TELNET access password does not
appear to be affected.
The failure has been reproduced in Cisco's laboratory, but only once.
Unfortunately the problem was reproduced only in the most preliminary stages
of Cisco's investigation. The conditions under which the failure occurs are
not known in detail.
Based on the information presently available, the source of the problem
seems to be that the LocalDirector "forgets" its configured enable password
upon being upgraded to version 1.6.x from an older software version. A
LocalDirector without a configured enable password still does prompt for a
password, even though that password is not checked. This means that the
system's administrator may not notice that the password has been lost for
quite some time, if ever.
Who is Affected
All LocalDirector customers should check to see that their enable passwords
are being enforced properly. Use the "enable" command to enter privileged
mode, and give an invalid password. If the invalid password is accepted, you
are affected.
If the invalid password is not accepted, you are not affected at present...
but bear in mind that we do not yet fully understand the conditions under
which passwords are lost. Until the problem is better understood, we suggest
that all LocalDirector customers, and especially all LocalDirector 1.6.3
customers, take special precautions as outlined in the "Workarounds" section
below.
This problem probably affects all 1.6.x versions of the LocalDirector
software. However, version 1.6.3 is the only 1.6.x version that has been
released to Cisco's general customer base, and Cisco discourages the use of
other 1.6.x versions because of possible software instability.
Because the LocalDirector code is almost entirely separate from the code
used in other Cisco products, it is extremely unlikely that any product
other than the LocalDirector is affected. Classic IOS, as used on Cisco
routers, shares absolutely no password or configuration management code with
the LocalDirector, and is therefore definitely not affected. WANBU and WBU
products, including Catalyst switches and FastPacket switches, are likewise
definitely not affected.
Impact
Any person who can log into an affected LocalDirector via TELNET or over its
its console port can reconfigure or shut down the LocalDirector.
Workarounds
Cisco recommends that customers take the following steps:
1. Consider putting off any software upgrades to version 1.6.3 that may be
scheduled for the week of November 17, 1997, pending new information.
We hope to have better information within a few working days.
2. Check to make sure that enable passwords are being enforced by all
LocalDirectors. If you find that a LocalDirector is not enforcing its
enable password, changing the password using the "enable password"
configuration command should reactivate the password. Remember to save
the new password using the "write memory" command. Recheck password
enforcement after any software upgrade or downgrade.
3. Make sure that you have configured a TELNET access password for your
LocalDirector using the "password" configuration command. If you're not
sure of the secrecy of your TELNET password, consider changing it. If
you allow unprivileged TELNET access by users who should not have
privileged access, consider denying those users access temporarily by
changing the TELNET password.
4. Consider disabling TELNET access altogether, and/or using firewalling
devices to block TELNET access from untrusted hosts, and/or restricting
access from remote hosts using the address-and-mask feature of the
LocalDirector "telnet" configuration command.
5. If you have a dialin modem connected to your LocalDirector's console
port, or if you have the console port connected to a network device
that allows remote access, either disconnect the console or protect it
using the authentication features of the modem or network device to
which it is connected.
Exploitation and Public Announcements
Cisco has had no reports of malicious exploitation of this vulnerability.
This vulernability was first brought to Cisco's attention by a public
announcement on the "[email protected]" mailing list on Thursday,
November 13, 1997. There has been some subsequent discussion on that mailing
list.
Future Work and Updates
Cisco will continue working to characterize this problem and to produce a
software fix. Updated versions of this notice will be posted on Cisco's
Worldwide Web site as more information becomes available. We hope to have
more information by 17:00 US/Pacific time on Monday, November 17, 1997, but
because of the unknown nature of the problem, we can make no guarantees.
Distribution of this Notice
This notice is being sent to the following Internet mailing lists and
newsgroups:
* [email protected]
* comp.dcom.sys.cisco
* [email protected]
* [email protected] (includes CERT/CC)
Updates will be sent to some or all of these, as appropriate.
This notice will be posted in the "Field Notices" section of Cisco's
Worldwide Web site, which can be found under "Technical Tips" in the
"Service and Support" section.. The copy on the Worldwide Web will be
updated as appropriate. For this notice only, Web posting is likely to lag
somewhat behind e-mail.
This notice is copyright 1997 by Cisco Systems, Inc. This notice may be
redistributed freely provided that redistributed copies are complete and
unmodified, including all date and version information.
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Date: Sun, 16 Nov 1997 09:06:02 -0800
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From: John Bashinski <jbash@CISCO.COM.>
Subject: Preliminary Notice: Cisco LocalDirector enable password loss
X-To: [email protected], [email protected]
X-Cc: [email protected]
To: [email protected]
Status:
X-PMFLAGS: 33554560 0
-----BEGIN PGP SIGNED MESSAGE-----
Preliminary Notice:
Cisco LocalDirector Enable Password Loss
November 15, 1997, 09:00 AM US/Pacific, Revision 1
- ------------------------------------------------------------------------
This is a preliminary notice describing a security problem about which there
has been customer concern. Cisco does not yet have full information about
this problem. Customers should use great caution in relying on the
information in this notice.
Summary
- -----
At least two customers have reported failures in the enable password
mechanism in version 1.6.3 of Cisco's LocalDirector product. Affected
systems allow users to enter privileged mode without providing the correct
enable password; any string will suffice as a password. This applies only to
the privileged-mode enable password; the TELNET access password does not
appear to be affected.
The failure has been reproduced in Cisco's laboratory, but not consistently.
The conditions under which the failure occurs are not known in detail.
Based on the information presently available, the source of the problem
seems to be that the LocalDirector "forgets" its configured enable password
upon being upgraded to version 1.6.x from an older software version. A
LocalDirector without a configured enable password still does prompt for a
password, even though that password is not checked. This means that the
system's administrator may not notice that the password has been lost for
quite some time, if ever.
Who is Affected
- -------------
All LocalDirector customers should check to see that their enable passwords
are being enforced properly. Use the "enable" command to enter privileged
mode, and give an invalid password. If the invalid password is accepted, you
are affected.
If the invalid password is not accepted, you are not affected at present...
but bear in mind that we do not yet fully understand the conditions under
which passwords are lost. Until the problem is better understood, we suggest
that all LocalDirector customers, and especially all LocalDirector 1.6.3
customers, take special precautions as outlined in the "Workarounds" section
below.
This problem probably affects all 1.6.x versions of the LocalDirector
software. However, version 1.6.3 is the only 1.6.x version that has been
released to Cisco's general customer base.
Because the LocalDirector code is almost entirely separate from the code
used in other Cisco products, it is extremely unlikely that any product
other than the LocalDirector is affected. Classic IOS, as used on Cisco
routers, shares absolutely no password or configuration management code with
the LocalDirector, and is therefore definitely not affected. Catalyst
switches and FastPacket switches are likewise definitely not affected.
Impact
- ----
Any person who can log into an affected LocalDirector via TELNET or over its
its console port can reconfigure or shut down the LocalDirector.
Workarounds
- ---------
Cisco recommends that customers take the following steps:
1. Consider postponing any scheduled software upgrades to version 1.6.3.
2. Check to make sure that enable passwords are being enforced by all
LocalDirectors. If you find that a LocalDirector is not enforcing its
enable password, changing the password using the "enable password"
configuration command should reactivate the password. Remember to save
the new password using the "write memory" command. Recheck password
enforcement after any software upgrade or downgrade.
3. Make sure that you have configured a TELNET access password for your
LocalDirector using the "password" configuration command. If you're not
sure of the secrecy of your TELNET password, consider changing it. If
you allow unprivileged TELNET access by users who should not have
privileged access, consider denying those users access temporarily by
changing the TELNET password.
4. If you have a dialin modem connected to your LocalDirector's console
port, or if you have the console port connected to a network device
that allows remote access, either disconnect the console or protect it
using the authentication features of the modem or network device to
which it is connected.
Exploitation and Public Announcements
- -----------------------------------
Cisco has had no reports of malicious exploitation of this vulnerability.
This vulernability was first brought to Cisco's attention by a public
announcement on the "[email protected]" mailing list on Thursday,
November 13. There has been some subsequent discussion on that mailing list.
Future Work and Updates
- ---------------------
Cisco will continue working to characterize this problem and to produce a
software fix. Updated versions of this notice will be posted on Cisco's
Worldwide Web site as more information becomes available.
Distribution of this Notice
- -------------------------
This notice is being sent to the following Internet mailing lists and
newsgroups:
* [email protected]
* comp.dcom.sys.cisco
* [email protected]
* [email protected] (includes CERT/CC)
Updates will be sent to some or all of these, as appropriate.
This notice will be posted in the "Field Alerts" section of Cisco's
Worldwide Web site. The copy on the Worldwide Web will be updated as
appropriate.
This notice is copyright 1997 by Cisco Systems, Inc. This notice may be
redistributed freely provided that redistributed copies are complete and
unmodified, including all date and version information.
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Reply-To: John Bashinski <jbash@CISCO.COM.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: John Bashinski <jbash@CISCO.COM.>
Subject: Re: What to do when you forget your cisco LD password...
X-To: Dustin Sallings <dustin@spy.net.>
X-Cc: [email protected], [email protected]
To: [email protected]
In-Reply-To: Your message of "14 Nov 1997 01:37:50 GMT."
<ML-3.3-SPY.879471470.6838.dustin@bleu.west.spy.net.>
Status:
X-PMFLAGS: 33554560 0
> If you're like me, you've got a lot of passwords to remember, and
> sometimes, well, we forget. There's good news, though! For a limited time
> only, you can enable on your cisco LocalDirector with the magic ^C password.
>
> I noticed this on a 1.6.3 LocalDirector where I mistyped the enable
> password by mistake and hit ^C to start over, but I didn't have to, took me
> right in, and let me make my configuration changes. Later experimentation
> showed that you don't even have to type in a partially invalid password, ^C
> alone seems to do the trick in all cases we tried.
I am not a LocalDirector expert and don't have access to a test machine,
but I just checked this with the Those Who Know. I am informed that
control-C will work as an enable password only if you haven't actually
set a password. In fact, *any* string will work if you haven't set a
password. If you've set an enable password on the box, control-C will
not work. This was verified by testing on a 1.6.3 LocalDirector.
If control-C worked for you on a machine with a password properly set,
*please* contact me directly with details of how you configured it.
You're right, however, that you shouldn't let people you don't trust log
in to your equipment in the first place.
-- John B.
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Reply-To: Lloyd Vancil <lev@apple.com.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: Lloyd Vancil <lev@apple.com.>
Subject: Re: Preliminary Notice: Cisco LocalDirector enable password loss
X-To: John Bashinski <jbash@cisco.com.>
To: [email protected]
Status:
X-PMFLAGS: 34078848 0
Being one of the customers involved in the below mentioned incident I
feel I must make a full confession ;)
Testing from the console and from a telnet session this morning shows
that the properly set and written to memory password appears secure.
None of my tests this morning succeeded in entering enable mode without a
full and valid password entry. I do not know what state the device was
in when the attempt outlined below succeeded and I have not been able to
duplicate it without removing the password and writing to memory without
a password set.
I would like to thank Cisco and John for their quick attention to this
matter. Cisco remains one of the most professional outfits out there.
Sincerly
Lloyd Vancil
>-----BEGIN PGP SIGNED MESSAGE-----
>
>Preliminary Notice:
>Cisco LocalDirector Enable Password Loss
>
>November 15, 1997, 09:00 AM US/Pacific, Revision 1
>- ------------------------------------------------------------------------
>
>This is a preliminary notice describing a security problem about which there
>has been customer concern. Cisco does not yet have full information about
>this problem. Customers should use great caution in relying on the
>information in this notice.
>
>Summary
>- -----
>At least two customers have reported failures in the enable password
>mechanism in version 1.6.3 of Cisco's LocalDirector product. Affected
>systems allow users to enter privileged mode without providing the correct
>enable password; any string will suffice as a password. This applies only to
>the privileged-mode enable password; the TELNET access password does not
>appear to be affected.
>
>The failure has been reproduced in Cisco's laboratory, but not consistently.
>The conditions under which the failure occurs are not known in detail.
>
>Based on the information presently available, the source of the problem
>seems to be that the LocalDirector "forgets" its configured enable password
>upon being upgraded to version 1.6.x from an older software version. A
>LocalDirector without a configured enable password still does prompt for a
>password, even though that password is not checked. This means that the
>system's administrator may not notice that the password has been lost for
>quite some time, if ever.
>
>Who is Affected
>- -------------
>All LocalDirector customers should check to see that their enable passwords
>are being enforced properly. Use the "enable" command to enter privileged
>mode, and give an invalid password. If the invalid password is accepted, you
>are affected.
>
>If the invalid password is not accepted, you are not affected at present...
>but bear in mind that we do not yet fully understand the conditions under
>which passwords are lost. Until the problem is better understood, we suggest
>that all LocalDirector customers, and especially all LocalDirector 1.6.3
>customers, take special precautions as outlined in the "Workarounds" section
>below.
>
>This problem probably affects all 1.6.x versions of the LocalDirector
>software. However, version 1.6.3 is the only 1.6.x version that has been
>released to Cisco's general customer base.
>
>Because the LocalDirector code is almost entirely separate from the code
>used in other Cisco products, it is extremely unlikely that any product
>other than the LocalDirector is affected. Classic IOS, as used on Cisco
>routers, shares absolutely no password or configuration management code with
>the LocalDirector, and is therefore definitely not affected. Catalyst
>switches and FastPacket switches are likewise definitely not affected.
>
>Impact
>- ----
>Any person who can log into an affected LocalDirector via TELNET or over its
>its console port can reconfigure or shut down the LocalDirector.
>
>Workarounds
>- ---------
>Cisco recommends that customers take the following steps:
>
> 1. Consider postponing any scheduled software upgrades to version 1.6.3.
> 2. Check to make sure that enable passwords are being enforced by all
> LocalDirectors. If you find that a LocalDirector is not enforcing its
> enable password, changing the password using the "enable password"
> configuration command should reactivate the password. Remember to save
> the new password using the "write memory" command. Recheck password
> enforcement after any software upgrade or downgrade.
> 3. Make sure that you have configured a TELNET access password for your
> LocalDirector using the "password" configuration command. If you're not
> sure of the secrecy of your TELNET password, consider changing it. If
> you allow unprivileged TELNET access by users who should not have
> privileged access, consider denying those users access temporarily by
> changing the TELNET password.
> 4. If you have a dialin modem connected to your LocalDirector's console
> port, or if you have the console port connected to a network device
> that allows remote access, either disconnect the console or protect it
> using the authentication features of the modem or network device to
> which it is connected.
>
>Exploitation and Public Announcements
>- -----------------------------------
>Cisco has had no reports of malicious exploitation of this vulnerability.
>
>This vulernability was first brought to Cisco's attention by a public
>announcement on the "[email protected]" mailing list on Thursday,
>November 13. There has been some subsequent discussion on that mailing list.
>
>Future Work and Updates
>- ---------------------
>Cisco will continue working to characterize this problem and to produce a
>software fix. Updated versions of this notice will be posted on Cisco's
>Worldwide Web site as more information becomes available.
>
>Distribution of this Notice
>- -------------------------
>This notice is being sent to the following Internet mailing lists and
>newsgroups:
>
> * [email protected]
> * comp.dcom.sys.cisco
> * [email protected]
> * [email protected] (includes CERT/CC)
>
>Updates will be sent to some or all of these, as appropriate.
>
>This notice will be posted in the "Field Alerts" section of Cisco's
>Worldwide Web site. The copy on the Worldwide Web will be updated as
>appropriate.
>
>This notice is copyright 1997 by Cisco Systems, Inc. This notice may be
>redistributed freely provided that redistributed copies are complete and
>unmodified, including all date and version information.
>
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-------------------------------------------------------------
* Why is 'abbreviation' such a long word?
-------------------------------------------------------------
[email protected]
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Date: Fri, 21 Nov 1997 00:38:10 -0600
Reply-To: Eric Thacker <eric@CAFFREY.NET.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: Eric Thacker <eric@CAFFREY.NET.>
Subject: Land and Cisco Routers.
To: [email protected]
Status:
X-PMFLAGS: 34078848 0
I just tested land.c on a cisco 753 router running version 4.0 of the os.
It DID freeze the router when I hit it on port 23. The router wasn't able
to reach the internal lan or the wan and some lights on the front of the
router were frozen also. I couldn't ping or telnet to the router, the
only way to restart it is a hard reboot.
If anyone knows if this also affects larger cisco routers (1000 series
through 7500) let me know or post it back here on bugtraq. As you can
see, there is a great potential of damage using this bug seeing as many of
the internet backbones are made up of cisco routers.
Eric Thacker | -= Stupid unix command #47 =-
System Administrator | $ drink < bottle; opener
Caffrey/Digilink Networks | bottle: cannot open
[email protected] | opener: not found
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Message-Id: <19971122185537.5608.qmail@susan.cisco.com.>
Date: Sat, 22 Nov 1997 10:55:37 -0800
Reply-To: John Bashinski <jbash@CISCO.COM.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: John Bashinski <jbash@CISCO.COM.>
Subject: Updated notice on Cisco and land.c
X-To: [email protected], [email protected], [email protected]
X-Cc: [email protected], [email protected], [email protected],
[email protected], [email protected], [email protected],
[email protected], [email protected], [email protected], [email protected],
[email protected], [email protected], [email protected],
[email protected], [email protected]
To: [email protected]
Status:
X-PMFLAGS: 33554560 0
This is an update to the previous notice. I originally planned just to have
this updated on the Web site and to post a pointer to the updated Web page,
but the Web posting seems to be taking a really long time, and I don't want
to delay the notice any longer. This version will eventually (probably by the
time most of you read this) be posted at
http://www.cisco.com/warp/public/770/land-pub.shtml
That URL will be updated with future versions. We probably won't send the
whole text out again.
Important differences between this notice and the last one:
o There are definitely versions of classis Cisco IOS software that are
badly affected by the land.c attack.
o The notice contains detailed information about which IOS versions are
affected.
o Catalyst 5000s, and probably other Catalyst switches, are affected.
o Various editing and advice changes... nothing really substantive.
-- John B.
-----BEGIN PGP SIGNED MESSAGE-----
Field Notice:
TCP loopback DoS Attack (land.c) and Cisco Devices
November 22, 1997, 08:00 AM US/Pacific, Revision 2
Summary
=======
Somebody has released a program, known as land.c, which can be used to
launch denial of service attacks against various TCP implementations. The
program sends a TCP SYN packet (a connection initiation), giving the target
host's address as both source and destination, and using the same port on
the target host as both source and destination.
Classic Cisco IOS software (used on Cisco routers with product numbers
greater than 1000, on the CGS/MGS/AGS+, and on the CS-500) is vulnerable to
this attack, depending on the software version. See the section on
"Affected Cisco IOS Software Versions" in this document for information on
affected versions.
Cisco IOS/700 software (used on Cisco 7xx routers) is also vulnerable. The
7xx vulnerability is more devastating than the classic Cisco IOS software
vulnerability, but probably less dangerous for most customers, since
firewalls separate most 7xx routers from the Internet.
Cisco Catalyst 5000 LAN switches are vulnerable. Other Cisco Catalyst
LAN switches are probably also vulnerable.
The PIX firewall appears does not appear to be affected. Initial testing of
the Centri firewall tends to indicate that it is not affected.
We're working on characterizing other products' vulnerability to attack.
Updates will be issued as information becomes available.
Who is Affected
===============
All Cisco IOS/700 software and Cisco Catalyst systems that can be reached
via TCP from untrusted hosts are affected. Cisco IOS software systems that
are running vulnerable versions and that can be reached via TCP from
untrusted hosts are affected. In all cases, the TCP ports reachable by the
attack must be ports on which services are actually being provided (such as
the TELNET port, for most systems). The attack requires spoofing the
targets's own address, so systems behind effective anti-spoofing firewalls
are safe.
Impact
======
This vulnerability allows attackers to deny service to legitimate users and
to administrators. Recovery may require physically visiting the affected
hardware. Appropriate firewalls can block this attack.
Classic Cisco IOS Software
- ------------------------
Classic Cisco IOS software versions fall into three groups in terms of
vulnerability. Highly vulnerable releases may hang indefinitely, requiring
hardware resets, when attacked. Moderately vulnerable releases will not
accept any new TCP connections for about 30 seconds after receiving an
attack packet, but will recover and will continue to forward packets.
Largely invulnerable releases will continue to operate normally with
negligible performance impact. See the section "Affected Cisco IOS Software
Versions" in this document for information on exactly which versions are
affected.
A configuration workaround for classic Cisco IOS software can prevent the
problem entirely, subject to performance restrictions, for any version from
9.21 onward. Cisco has already released software fixes that protect some
Cisco IOS software versions, and plans to release those fixes for other
affected versions.
Cisco IOS/700 Software and 7xx Systems
- ------------------------------------
Cisco 7xx systems subjected to the attack will hang indefinitely and must be
physically reset. A configuration workaround for Cisco IOS/700 software can
prevent the problem entirely. Cisco plans to release a software fix for this
problem.
Cisco Catalyst LAN Switches
- -------------------------
Cisco Catalyst switches subjected to the attack will hang indefinitely and
must be reset. Not all Catalyst products have been tested, but this is
definitely true of the Catalyst 5000 series, and is expected to be true of
all Catalyst switches. The only workaround is to remove the IP address from
the Catalyst switch, or to protect the switch by firewalling it using router
access lists or dedicated firewall products. Cisco plans to release a
software fix for this problem.
Other Cisco Products
Initial tests indicate that the PIX firewall is not vulnerable to this
attack. Tests have been conducted with versions 4.1.3.245 and 4.0.7.
Initial tests indicate that the Centri firewall (build 4.110) is not
vulnerable to this attack with no exposed services configured. We have not
yet tested the Centri product with exposed services.
Cisco IOS Software Details
Affected Cisco IOS Software Versions and Software Upgrades
- --------------------------------------------------------
There are two bugs that make Cisco IOS software vulnerable to this attack.
Fixes exist in the field for both bugs. Bug ID CSCdi71085 makes systems
highly vulnerable to the attack. Bug ID CSCdi87533 makes systems moderately
vulnerable. Bug ID CSCdj61324 is a newly-created bug ID that is being used
as a tag for integration of the fix for CSCdi87533, plus a largely cosmetic
change that prevents even the temporary creation of a half-open
connection.The fix for CSCdj61324 has not yet been integrated into any
released code, but is not necessary if the fix for CSCdi87533 is present.
CSCdi71085 and CSCdj87533 divide Cisco IOS software versions into three
vulnerability classes. Versions that do not have the fix for bug ID
CSCdi71085 are highly vulnerable, and may hang indefinitely, requiring
hardware resets, when attacked. This includes all releases before release
10.3, as well as early 10.3, 11.0, 11.1, and 11.2 versions.
Versions in which CSCdi71085 has been fixed, but in which CSCdi87533 is
still present, are moderately vulnerable to the attack. These versions will
not accept any new TCP connections for about 30 seconds after any attack
packet is received, but will not hang completely, will continue to forward
packets without interruption, and will recover with no long-term effects.
CSCdi87533 has thus far been fixed only in 11.2-based releases; the fix was
integrated in 11.2(3.4), 11.2(3.4)F, and 11.2(3.4)P.
Versions in which both CSCdi71085 and CSCdi87533 have been fixed are largely
invulnerable to this attack. These versions will create half-open TCP
connections upon receiving attack packets, but will continue to accept
legitimate TCP connections, and will delete the half-open connections within
about 30 seconds. The performance impact of such a half-open connection
during its lifetime is believed to be negligible.
Future versions in which CSCdj61324 has been fixed will be invulnerable to
the attack, and will not create half-open connections in response to attack
packets. We believe the security advantage of the CSCdj61324 fix over the
CSCdj87533 fix to be negligible; CSCdj61324 is largely a placeholder to be
used for integrating fixes in future non-11.2 releases.
If you believe that there is any possibility of hostile attack against your
system, and if you cannot protect yourself using the configuration
workaround given above, we strongly recommend that you upgrade to a versions
containing the fix for CSCdi71085, since the impact of CSCdi71085 under this
attack is very high. The fix for CSCdi71085 is available for releases based
on 10.3, 11.0, 11.1, and 11.2, and has been in the field for quite some
time. Users of 11.2-based releases should upgrade to post-11.2(4) versions,
thereby getting the fix for CSCdi87533 as well.
Cisco intends to release fixes for CSCdj61324 (equivalent to CSCdi87533) on
non-11.2 releases. The timetable for releasing these fixes has not yet been
set.
At the time of this writing, the following releases are recommended:
First released versions with
all existing fixes (*= fix for Recommended for most
Base Release CSCdi87533) installations
------------ ------------------------------ --------------------
10.3 10.3(16) 10.3(19a)
11.0 11.0(12), 11.0(12a)BT 11.0(17), 11.0(17)BT
11.1 11.1(7), 11.1(7)AA, 11.1(7)CA, 11.1(15), 11.1(15)AA,
11.1(9)IA 11.1(15)CA, 11.1(15)IA
11.2 11.2(4)*, 11.2(4)F*, 11.2 11.2(10), 11.2(9)P,
11.2(4)F1
Before 10.3 End of engineering 10.3(19a)
As with any software upgrade, you should make sure your system configuration
is supported by the new software before upgrading. It's especially important
to make sure that your system has sufficient memory to support the new
software. Upgrade planning assistance is available from Cisco's Worldwide
Web site at http://www.cisco.com/.
Workaround for Classic Cisco IOS Software
- ---------------------------------------
Classic Cisco IOS software users can use input access lists on their
interfaces to prevent the attack packets from entering their TCP stacks.
Input access lists are available in all Cisco IOS software versions from
9.21 onward. Using an input access list will prevent the attack entirely,
but may have unacceptable performance impacts on heavily loaded high-end
routers. Traffic will still be fast-switched, but higher-speed switching
modes may be disabled by the use of the input access lists. Use care in
deploying this workaround on heavily loaded routers.
If you have no existing input access lists, create a new IP extended access
list. Use a presently-unused number between 100 and 199. The access list
must have an entry for each IP address configured on the system. Deny
packets from each address to itself. For example:
access-list 101 deny tcp 1.2.3.4 0.0.0.0 1.2.3.4 0.0.0.0
access-list 101 deny tcp 5.6.7.8 0.0.0.0 5.6.7.8 0.0.0.0
access-list 101 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
If you have existing access lists, you'll need to merge the new entries in
an appropriate way, generally at the top of the list. The access list should
be applied incoming on all interfaces, so a fragment of a total router
configuration might look like this:
interface ethernet 0
ip address 1.2.3.4 255.255.255.0
ip access-group 101 in
!
interface ethernet 1
ip address 5.6.7.8
ip access-group 101 in
!
access-list 101 deny tcp 1.2.3.4 0.0.0.0 1.2.3.4 0.0.0.0
access-list 101 deny tcp 5.6.7.8 0.0.0.0 5.6.7.8 0.0.0.0
access-list 101 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
Cisco IOS/700 Software Details
All Cisco IOS/700 software versions are vulnerable to this attack. Cisco
plans to release a software fix. The time of release has not been set.
Workaround for Cisco IOS/700
- --------------------------
Add the following configuration command to any profile that may be active
when connected to a potentially hostile network:
set ip filter tcp in source <7xx IP address> destination <7xx IP address> block
This will completely protect the 7xx system. We believe that 7xx
configurations in which this command has unacceptable performance or other
impact are extremely rare if they exist at all.
Cisco Catalyst LAN Switch Details
Cisco Catalyst 5000 LAN switches are vulnerable to attack. Other Cisco
Catalyst LAN switches are believed to be vulnerable. Cisco plans to release
software fixes for the vulnerability. The time of release has not been set.
The attack may be avoided by not assigning an IP address to the Catalyst
switch. However, this has the effect of disabling all remote management.
Depending on its location in the network, it may be possible to protect the
switch with router access lists or dedicated firewalls. An example of an
appropriate Cisco router access list entry for specifically protecting an
individual switch would be:
access-list 101 deny ip <switch-address> 0.0.0.0 <switch-address> 0.0.0.0
Note that this is not a complete access list. Other, more general filters
are feasible.
Using Cisco Products to Protect Other Systems
We do not believe that this attack can be used against systems behind our
dedicated firewall products, the PIX and Centri firewalls, unless
general-purpose tunnels have been enabled through the firewalls. Such
configurations are not recommended and we believe them to be uncommon.
Properly designed anti-spoofing access lists at border routers can be used
to prevent the attack from entering a private network from the Internet. Use
the access lists to filter out packets whose IP source addresses are on your
internal net, but which are arriving from interfaces connected to the
outside Internet.
Exploitation and Public Announcements
Cisco has had multiple reports of this vulnerability.
Most exploitation seems to be using the original program, which sends one
packet at a time. Floods of invalid packets have not been reported.
This issue has been widely discussed in a variety of Internet forums.
Exploitation code is widely available to the public.
Cisco first heard of this problem on the morning of Friday, November 21.
Distribution of this Notice
This notice is being sent to the following Internet mailing lists and
newsgroups:
* [email protected]
* comp.dcom.sys.cisco
* [email protected]
* [email protected] (includes CERT/CC)
* [email protected]
Updates will be sent to some or all of these, as appropriate.
This notice will be posted in the "Field Notices" section of Cisco's
Worldwide Web site, which can be found under "Technical Tips" in the
"Service and Support" section. The URL will be
http://www.cisco.com/warp/public/770/land-pub.shtml
The copy on the Worldwide Web will be updated as appropriate.
Cisco Security Procedures
Please report security issues with Cisco products to
[email protected].
Revision History
================
Revision 1, 14:00,
21-NOV-1997 Initial revision
Revision 2, 08:00 Add information about highly vulnerable
22-NOV-1997 IOS versions. Add detailed information about
affected version numbers. Add specific bug IDs.
Add upgrade recommendations. Add first
information about Catalyst LAN switches. General
editing and reformatting.
This notice is copyright 1997 by Cisco Systems, Inc. This notice may be
redistributed freely provided that redistributed copies are complete and
unmodified, including all date and version information.
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Reply-To: John Bashinski <jbash@CISCO.COM.>
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From: John Bashinski <jbash@CISCO.COM.>
Subject: Field Notice: TCP loopback DoS Attack (land.c) and Cisco Devices
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-----BEGIN PGP SIGNED MESSAGE-----
Field Notice:
TCP loopback DoS Attack (land.c) and Cisco Devices
November 21, 1997, 14:00 AM US/Pacific, Revision 1
- --------------------------------------------------
Summary
- -----
Somebody has released a program, known as land.c, which can be used to
launch denial of service attacks against various TCP implementations. The
program sends a TCP SYN packet (a connection initiation), giving the target
host's address as both source and destination, and using the same port on
the target host as both source and destination.
Classic IOS software (used on Cisco routers with product numbers greater
than 1000, on the CGS/MGS/AGS+, and on the CS-500) is moderately vulnerable
to this attack. For some IOS versions, if the attack is launched against a
TCP port that is actually listening (say the TELNET port), then invalid
connection data will be created, preventing further legitimate connections
for approximately 30 seconds. High CPU loads may result on some IOS
versions. We observed a complete hang on one 11.5 system, but have been
unable to reproduce that failure. Based on very preliminary data, the
router's packet forwarding functions are not generally affected.
IOS/700 (used on Cisco 7xx routers) is also vulnerable. The 7xx
vulnerability is more devastating than the classic IOS vulnerability, but
probably less dangerous for most customers, since firewalls separate most
7xx routers from the Internet.
The PIX firewall appears does not appear to be affected. Initial testing of
the Centri firewall tends to indicate that it is not affected.
We're working on characterizing other products' vulnerability to attack.
Updates will be issued as information becomes available.
Who is Affected
- -------------
All IOS and IOS/700 systems that can be reached via TCP from untrusted hosts
are affected, provided that the reachable TCP ports are ports on which IOS
ordinarily provides service. The attack requires spoofing the targets's own
address, so systems behind effective anti-spoofing firewalls are safe.
Impact
- ----
Classic IOS systems may experience slowdowns while under active attack. On
IOS software versions earlier than 11.2(4), new TCP connections will fail
for a period of about 30 seconds after any attack packet is received. IOS
versions later than 11.2(4), or that contain the fix for bug ID CSCdi87533,
may experience slowdowns, but should continue to accept new TCP connections
. Most IOS versions appear to recover completely within a few minutes of the
attack stopping, but we have not yet fully characterized the effect on all
IOS versions. One complete failure was observed; the version was 11.1(5). A
configuration workaround for classic IOS can prevent the problem entirely,
subject to performance restrictions.
IOS/700 systems subjected to the attack will hang indefinitely and must be
physically reset. A configuration workaround for IOS/700 can prevent the
problem entirely.
Initial tests indicate that the PIX firewall is not vulnerable to this
attack. Tests have been conducted with version 4.1.3.245 and 4.0.7.
Initial tests indicate that the Centri firewall (build 4.110) is not
vulnerable to this attack with no exposed service configured. We have not
yet tested the Centri product with exposed services.
Workaround for Classic IOS
- ------------------------
Classic IOS users can use input access lists on their interfaces to prevent
the attack packets from entering their TCP stacks. This will prevent the
attack entirely, but may have unacceptable performance impacts on heavily
loaded high-end routers. Traffic will still be fast-switched, but
higher-speed switching modes may be disabled. It should be tried with care.
If you have no existing input access lists, create a new IP extended access
list. Use a presently-unused number between 100 and 199. The access list
must have an entry for each of the IP address configured on the system.
Deny packets from each address to itself. For example:
access-list 101 deny tcp 1.2.3.4 0.0.0.0 1.2.3.4 0.0.0.0
access-list 101 deny tcp 5.6.7.8 0.0.0.0 5.6.7.8 0.0.0.0
access-list 101 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
If you have existing access lists, you'll need to merge the new entries in
an appropriate way, generally at the top of the list. The access list should
be applied incoming on all interfaces, so a fragment of a total router
configuration might look like this:
interface ethernet 0
ip address 1.2.3.4 255.255.255.0
ip access-group 101 in
!
interface ethernet 1
ip address 5.6.7.8
ip access-group 101 in
!
access-list 101 deny tcp 1.2.3.4 0.0.0.0 1.2.3.4 0.0.0.0
access-list 101 deny tcp 5.6.7.8 0.0.0.0 5.6.7.8 0.0.0.0
access-list 101 permit ip 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255
Workaround for IOS/700
- --------------------
Add the following configuration command to any profile that may be active
when connected to potentially hostile network:
set ip filter tcp in source <7xx IP address> destination <7xx IP address> block
Using Cisco Products to Protect Other Systems
- -------------------------------------------
We do not believe that this attack can be used against systems behind our
dedicated firewall products, the PIX and Centri firewalls, unless
general-purpose tunnels have been enabled through the firewalls.
Properly designed anti-spoofing access lists at border routers can be used
to prevent the attack from entering a private network from the Internet. Use
the access lists to filter out packets whose IP source addresses are on your
internal net, but which are arriving from interfaces connected to the
outside Internet.
Exploitation and Public Announcements
- -----------------------------------
Cisco has had multiple reports of this vulnerability.
Most exploitation seems to be using the original program, which sends one
packet at a time. Floods of invalid packets have not been reported.
This issue has been widely discussed in a variety of Internet fora.
Cisco first heard of this problem on the morning of Friday, November 21.
Distribution of this Notice
- -------------------------
This notice is being sent to the following Internet mailing lists and
newsgroups:
* [email protected]
* comp.dcom.sys.cisco
* [email protected]
* [email protected] (includes CERT/CC)
* [email protected]
Updates will be sent to some or all of these, as appropriate.
This notice will be posted in the "Field Notices" section of Cisco's
Worldwide Web site, which can be found under "Technical Tips" in the
"Service and Support" section. The URL will be
http://www.cisco.com/warp/public/770/land-pub.shtml
The copy on the Worldwide Web will be updated as appropriate.
Cisco Security Procedures
- -----------------------
Please report security issues with Cisco products to
[email protected].
This notice is copyright 1997 by Cisco Systems, Inc. This notice may be
redistributed freely provided that redistributed copies are complete and
unmodified, including all date and version information.
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Message-Id: <Pine.LNX.3.96.971121165058.13689A-100000@ns.bis.bg.>
Date: Fri, 21 Nov 1997 17:01:28 +0200
Reply-To: Stefan Stefanov <stefan@NS.BIS.BG.>
Sender: Bugtraq List <BUGTRAQ@NETSPACE.ORG.>
From: Stefan Stefanov <stefan@NS.BIS.BG.>
Subject: land protection for cisco
To: [email protected]
Status:
X-PMFLAGS: 34078848 0
hi.
Here is a simple protection against the land stuff for the cisco's. It's a
extended ip access list that should be put on all the intefaces on the
box.
Extended IP Access list 105
deny tcp host 111.111.111.111 host 111.111.111.111
permit ip any any
where 111.111.111.111 is the interface's ip address. This should be put
as
an input access-group.
Or if you don't get it here's what to type on your cisco's console.
rtr#config terminal
rtr(config)#access-list 105 deny tcp 111.111.111.111 0.0.0.0 111.111.111.111 0.0.0.0
rtr(config)#access-list 105 permit ip any any
rtr(config)#interface ethernet 0
rtr(config)#ip access-group 105 in
rtr(config)#exit
rtr(config)#interface serial 0
rtr(config)#ip access-group 105 in
and so on for the rest of the interfaces... Replace 105 with a free
extended access-list number.
I have tested it on our cisco 2511 and it works just ok.
Best regards, Stefan Stefanov.
WWW: http://www.bis.bg/~stefan
E-mail: [email protected]
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Reply-To: Richard Huddleston <huddler@EARTHLINK.NET.>
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From: Richard Huddleston <huddler@EARTHLINK.NET.>
Subject: Re: land protection for cisco
X-To: Stefan Stefanov <stefan@NS.BIS.BG.>
To: [email protected]
In-Reply-To: <Pine.LNX.3.96.971121165058.13689A-100000@ns.bis.bg.>
Status:
Minor corrections:
1) Each interface typically belongs to a distinct network, and therefore
typically has a unique IP address. Setting up a SINGLE access-group,
with the SINGLE address of one of your interfaces as its filtering rule,
and then applying that SINGLE access-group to each of your interfaces
(i.e., different IP addresses) won't work. (A router already implements
such a "rule" by the very nature of what it does: by forwarding packets
for a given address through the proper route, it does not forward packets
through inappropriate routes. The access-group rule given would be
vacuous for every interface except the one matching its IP address rule.)
I'd suggest that you create an access-group for EACH interface, and then
apply the appropriate one to the given interface.
2) If you're trying to protect internal devices, as well, you may as well
go ahead and filter for the entire subnet with the access-group definition.
That way, you'll nail both attempts to hit the router interface per se, and
block attempts to get through to internal machines.
./R*
At 05:01 PM 11/21/97 +0200, Stefan Stefanov wrote:
>hi.
>
>Here is a simple protection against the land stuff for the cisco's. It's a
>extended ip access list that should be put on all the intefaces on the
>box.
>
>Extended IP Access list 105
>deny tcp host 111.111.111.111 host 111.111.111.111
>permit ip any any
>
>where 111.111.111.111 is the interface's ip address. This should be put
>as
>an input access-group.
>
>Or if you don't get it here's what to type on your cisco's console.
>
>rtr#config terminal
>rtr(config)#access-list 105 deny tcp 111.111.111.111 0.0.0.0
111.111.111.111 0.0.0.0
>rtr(config)#access-list 105 permit ip any any
>rtr(config)#interface ethernet 0
>rtr(config)#ip access-group 105 in
>rtr(config)#exit
>rtr(config)#interface serial 0
>rtr(config)#ip access-group 105 in
>
>and so on for the rest of the interfaces... Replace 105 with a free
>extended access-list number.
>
>I have tested it on our cisco 2511 and it works just ok.
>
>Best regards, Stefan Stefanov.
>
>WWW: http://www.bis.bg/~stefan
>E-mail: [email protected]
>
>
--
Somewhere lurking in the Ort Cloud there's a fifty-mile-wide asteroid
with our name on it. We deserve it. -- Alan C. Hines <ach@io.com.>
huddler at earth link dot net
