X-RDate: Thu, 19 Feb 1998 10:54:37 +0500 (ESK)
Date: Tue, 10 Feb 1998 12:06:10 -0500 (EST)
From: [email protected]
To: [email protected]Subject: BoS: IBM-ERS Security Vulnerability Alert: IBM AIX: Insecure temporary files allow symbolic link attacks
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EMERGENCY RESPONSE SERVICE
SECURITY VULNERABILITY ALERT
10 February 1998 17:00 GMT Number: ERS-SVA-E01-1998:002.1
VULNERABILITY SUMMARY
VULNERABILITY: Insecure temporary files allow symbolic link attacks
PLATFORMS: IBM AIX(r) 3.2.5, 4.1.x, 4.2.x, 4.3
SOLUTION: Apply the fixes listed below.
THREAT: Local users can modify system files.
DETAILED INFORMATION
I. Description
Several insecure temporary files have been identified in AIX that will follow
symbolic links when they are created. In addition, these temporary files are
created with world-writable permissions. This can lead to denial of service
attacks.
II. Impact
If the root user executes one of the vulnerable commands while a symbolic link
from the corresponding temporary file exists, then the link will be followed
and overwrite or create arbitrary system files.
The vulnerable commands are not installed as set-user-id programs, thus,
unpriviledged users cannot create files in system directories. However, the
root user may be tricked into executing the programs while the symbolic link
is in place.
III. Details
The following is a list of world-writable files with workaround and fix
information:
==============
/tmp/last_uuid
==============
This file is created and used by the License Management subsystem and must be
world-writable in order to function correctly.
APAR:
Not available.
Workaround:
Ensure that /tmp/last_uuid is a regular file and owned by root. This can
be done by modifying /sbin/rc.boot to re-create this file during system
boot.
#!/usr/bin/ksh
cd /sbin
cp -p rc.boot rc.boot.before.security.patch
/bin/rm -f /tmp/last_uuid
>/tmp/last_uuid
chown root.system /tmp/last_uuid
chmod 666 /tmp/last_uuid
/usr/bin/ex <<EOF /sbin/rc.boot >/dev/null 2>&1
/rm -f \/etc\/lock/a
/bin/rm -f /tmp/last_uuid
>/tmp/last_uuid
chown root.system /tmp/last_uuid
chmod 666 /tmp/last_uuid
.
x!
EOF
/var/adm/ras/dumpsymplog
/var/adm/ras/dumpsymplog is used for storing the dump symptom string.
APAR:
Fixed in 4.2.1 maintenance level (IX58183)
Fixed in 4.3.0 release
Workaround:
If the file exists, change the permissions to 644. Add "umask 022" to
/usr/lib/ras/logsymptom.
/tmp/x, /var/adm/ras/$
/tmp/x and /var/adm/ras/$ are not needed.
APAR:
Fixed in 4.2.1 maintenance level (IX58183)
Fixed in 4.3.0 release.
Workaround:
Remove both files and change /usr/lib/ras/notifymeth so that they are not
re-created.
===============
/tmp/rc.net.out
===============
This file is used to log the output of rc.net and rc.bsdnet.
APAR:
Fixed in 4.3.0 release.
Workaround:
If the file exists, change the permissions to 644. Add "umask 022" to
/etc/rc.net and /etc/rc.bsdnet
=============
/tmp/xlogfile
=============
This file is used to log error messages from the X server.
APAR:
Fixed in 4.1.5 APAR IX58516 (fileset X11.base.rte.4.1.5.0)
Fixed in 4.2.1 maintenance level (IX58183)
Fixed in 4.3.0 release
Workaround:
Remove /tmp/xlogfile before and after starting the X server. This can be
done by changing /usr/lpp/X11/defaults/xserverrc.
/tmp/.oslevel.mlcache.info
This file must be world-writable in order for the oslevel command to function
correctly.
APAR:
Fixed in 4.1.5 APAR IX56229 (fileset bos.rte.install.4.1.5.0)
Fixed in 4.2.1 maintenance level (IX58183)
Fixed in 4.3.0 release
Workaround:
Ensure that /tmp/.oslevel.mlinfo.cache is a regular file and owned by root.
This can be done by modifying /sbin/rc.boot to re-create this file during
system boot.
=================
/tmp/sysdumpdev-L
=================
This file contains information processed by /usr/lib/ras/logsymptom. It is
not needed after logsymptom has finished execution.
APAR:
Not available.
Workaround:
Remove /tmp/sysdumpdev-L if it exists. Update /usr/lib/ras/logsymptom.
#!/usr/bin/ksh
/bin/rm -f /tmp/sysdumpdev-L
cd /usr/lib/ras
cp -p logsymptom logsymptom.before.security.patch
/usr/bin/ex <<EOF /usr/lib/ras/logsymptom >/dev/null 2>&1
/^tmpf=
a
/bin/rm -f \$tmpf
umask 022
.
x!
EOF
IV. Acknowledgements
Thanks to Joerg Schumacher <schuma@gaertner.de.>, for bringing this problem to
our attention.
VI. Contact Information
Comments regarding the content of this announcement can be directed to the IBM
Support Center or to:
[email protected]
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Copyright 1998 International Business Machines Corporation.
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