Date: Tue, 17 Aug 2004 13:48:27 -0400
From: NetBSD Security-Officer <security-officer@netbsd.org.>
To: [email protected]Subject: NetBSD Security Advisory 2004-009: ftpd root escalation
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NetBSD Security Advisory 2004-009
Topic: ftpd root escalation
Version: NetBSD-current: source prior to Aug 10, 2004
NetBSD 2.0 branch: source prior to Aug 15, 2004
NetBSD 1.6.2: affected
NetBSD 1.6.1: affected
NetBSD 1.6: affected
NetBSD-1.5.3: affected
NetBSD-1.5.2: affected
NetBSD-1.5.1: affected
NetBSD-1.5: affected
pkgsrc: net/lukemftpd all versions
pkgsrc: net/tnftpd prior to tnftpd-20040810
Severity: Remote root for systems providing ftpd service
Fixed: NetBSD-current: Aug 10, 2004
NetBSD-2.0 branch: Aug 15, 2004 (2.0 will include the fix)
NetBSD-1.6 branch: Pullups not yet issued.
See Solutions section.
(1.6.3 will include the fix)
NetBSD-1.5 branch: Pullups not yet issued.
See Solutions section.
pkgsrc net/lukemftpd: Update pkgsrc, this package was
renamed to tnftpd
net/tnftpd: tnftpd-20040810 corrects this issue
Abstract
========
A set of flaws in the ftpd source code can be used together to
achieve root access within an ftp session. With root file manipulation
ability, mechanisms to gain a shell are numerous, so this issue
should be considered a remote root situation.
ftpd is disabled by default in NetBSD since NetBSD-1.5.3, however
many users might have reason to provide this popular service.
Technical Details
=================
Przemyslaw Frasunek is going to release a detailed analysis very
shortly. A URL will be provided here when available.
Since this serious issue affects many users, we won't share information
in this version of the advisory, as it would ease development of
exploits.
Solutions and Workarounds
Confirm that the host in question is running ftpd, by checking the ftp
entries in /etc/inetd.conf. By default, the entries look like this:
#ftp stream tcp nowait root /usr/libexec/ftpd ftpd -ll
#ftp stream tcp6 nowait root /usr/libexec/ftpd ftpd -ll
If the comment character (#) has been removed from the start of the
lines, then ftp has been enabled on this host. Hosts not running ftpd
are not vulnerable, but ftpd should be updated to prevent future
exposure if ftpd is enabled at a later date.
If ftpd has been configured to run with the -r option, then your server
is not vulnerable. Adding -r may be an acceptable workaround for some
sites, until ftpd can be upgraded.
To determine if a host is running a vulnerable version of ftpd, compare
the version string in the login banner (if displayed).
Any version of lukemftpd,
any version of NetBSD-ftpd prior to 20040809, or
any version of tnftpd prior to 20040810 is vulnerable.
% ftp ftp.server.host
Connected to ftp.server.host.
220 ftp.server.host FTP server (tnftpd 20040810) ready.
^^^^^^^^^^^^^^^
Patched ftp server.
* Workaround: Disable ftpd
As root, comment out the ftp lines in /etc/inetd.conf,
and execute the following command to disable ftpd:
% /etc/rc.d/inetd reload
Even if you plan to update ftpd, it is worthwhile to
disable ftpd until it is upgraded, in case you are
distracted and do not complete the update in a timely
fashion.
* Workaround: Drop root privileges
As root, add -r to the command line options for any
ftp entry in /etc/inetd.conf. Then run:
% /etc/rc.d/inetd reload
This option may not be acceptable at all sites, since
client compatibility issues are possible. See the
ftpd manpage for more details about -r.
If all untrusted user accounts are listed in /etc/ftpchroot, then the
root file access gained will only be effective inside the chrooted
directory. This is not a guarantee against further privilege
escalation, especially in concert with social engineering.
If you have ftp servers that run in chrooted environments, make sure to
update ftpd binaries in chrooted copies of /usr/libexec or
/usr/pkg/libexec, and ensure that inetd.conf points to the correct
executable.
The following instructions describe how to upgrade your ftpd
binaries by updating your source tree and rebuilding and
installing a new version of ftpd.
* NetBSD-current:
Systems running NetBSD-current dated from before 2004-08-09
should be upgraded to NetBSD-current dated 2004-08-10 or later.
The following directories need to be updated from the
netbsd-current CVS branch (aka HEAD):
src/libexec/ftpd
To update from CVS, re-build, and re-install ftpd:
# cd src
# cvs update -d -P src/libexec/ftpd
# cd src/libexec/ftpd
# make USETOOLS=no cleandir dependall
# make USETOOLS=no install
* NetBSD 2.0_BETA:
The binary distribution of NetBSD 2.0_BETA is vulnerable.
Systems running NetBSD 2.0_BETA dated from before 2004-08-14
should be upgraded to NetBSD 2.0_BETA dated 2004-08-15 or later.
The following directories need to be updated from the
netbsd-2-0 CVS branch:
src/libexec/ftpd
To update from CVS, re-build, and re-install ftpd:
# cd src
# cvs update -d -P src/libexec/ftpd
# cd src/libexec/ftpd
# make USETOOLS=no cleandir dependall
# make USETOOLS=no install
* NetBSD 1.6, 1.6.1, 1.6.2:
* NetBSD 1.5, 1.5.1, 1.5.2, 1.5.3:
* NetBSD prior to 1.5:
The binary distribution of NetBSD 1.6.2 and all prior releases
are vulnerable.
Pullups will be issued to the release branches of NetBSD-1-6,
and NetBSD-1-5.
Systems with these releases which need to run ftpd prior to
those pullups should be updated from pkgsrc using
net/tnftpd-20040810 or later.
% rm /usr/libexec/ftpd
% cd /usr/pkgsrc/net/tnftpd
% cvs update -dP
% make update
Then modify the relevant lines in /etc/inetd.conf to refer to
/usr/pkg/libexec/tnftpd instead of /usr/libexec/ftpd as follows:
#ftp stream tcp nowait root /usr/pkg/libexec/tnftpd ftpd -ll
#ftp stream tcp6 nowait root /usr/pkg/libexec/tnftpd ftpd -ll
Thanks To
=========
Przemyslaw Frasunek for notification, analysis, and discussion
Luke Mewburn for patches
Revision History
================
2004-08-17 Initial release
2004-08-17 Clarify Workarounds
More Information
================
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2004-009.txt.asc
Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.
Copyright 2004, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
$NetBSD: NetBSD-SA2004-009.txt,v 1.4 2004/08/17 17:44:58 david Exp $
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