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AUSCERT External Security Bulletin Redistribution
ESB-2007.0612 -- [AIX]
AIX at Command Buffer Overflow Vulnerability
13 August 2007
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AusCERT Security Bulletin Summary
---------------------------------
Product: at
Publisher: IBM
Operating System: AIX 5.2
AIX 5.3
Impact: Root Compromise
Access: Existing Account
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IBM SECURITY ADVISORY
First Issued: Tue Aug 7 17:42:20 CDT 2007
===============================================================================
VULNERABILITY SUMMARY
VULNERABILITY: AIX at Command Buffer Overflow Vulnerability
PLATFORMS: AIX 5.3
SOLUTION: Apply the APAR, interim fix or workaround as described
below.
THREAT: An attacker may run arbitrary code with root privileges.
CERT VU Number: n/a
CVE Number: n/a
===============================================================================
DETAILED INFORMATION
I. OVERVIEW
The 'at' command reads from standard input the names of commands to be run
at a later time and allows you to specify when the commands should be run.
II. DESCRIPTION
A buffer overflow vulnerability exists in the at command whereby a
local user may execute arbitrary code with root privileges.
III. IMPACT
The successful exploitation of this vulnerability allows a non-privileged
user to execute code with root privileges.
IV. PLATFORM VULNERABILITY ASSESSMENT
To determine if your system is vulnerable, run the following command:
# lslpp -l | grep bos.rte.cron
The following filesets levels are vulnerable:
AIX Level Lower Level Upper Level
-------------------------------------------------
5.3.0 5.3.0.0 5.3.0.60
NOTE: IBM only supports the latest two releases (AIX 5.2 & 5.3) and the
latest three Technology Levels (AIX 5.2 TL08, TL09, TL10 & AIX 5.3 TL04,
TL05, TL06). Affected customers are urged to upgrade to the latest
applicable Technology Level and Service Pack.
V. SOLUTIONS
A. APARS
IBM provides the following fixes:
AIX Level APAR number Availability
--------------------------------------------------------------------
5.3.0 IZ00139 Available
AIX Version 5 APARs can be downloaded from:
http://www.ibm.com/servers/eserver/support/unixservers/aixfixes.html
NOTE: Affected customers are urged to upgrade to the latest applicable
Technology Level and Service Pack.
B. INTERIM FIXES
Interim fixes are available. The interim fix can be downloaded via
ftp from:
ftp://aix.software.ibm.com/aix/efixes/security/at_ifix.tar.Z
This is a compressed tarball containing this advisory, interim fix
packages and PGP signatures for each package. The interim fixes below
include prerequisite checking. This will enforce the correct mapping
between the fixes and AIX Technology Levels.
AIX Release & Technology Level Interim fix
---------------------------------------------------------------
5300-04 IZ00139_04.070614.epkg.Z
5300-05 IZ00139_05.070614.epkg.Z
5300-06 IZ00139_06.070618.epkg.Z
IMPORTANT: If possible, it is recommended that a mksysb backup of the
system be created. Verify it is both bootable and readable before
proceeding.
These interim fixes have not been fully regression tested; thus, IBM
does not warrant the fully correct functionality of the interim fix.
Customers install the interim fix and operate the modified version of
AIX at their own risk.
Verify you have retrieved the fixes intact:
The interim fixes below are named by using the technology level
corresponding to the release that the fix applies to. The checksums
below were generated using the "sum" and "md5sum" commands and are as
follows:
Filename sum md5sum
----------------------------------------------------------------------
IZ00139_04.070614.epkg.Z 48571 93 846844e63c1a448839b671d6387cca30
IZ00139_05.070614.epkg.Z 43020 94 1b8f331215ecc7ba5b65ec046b0cd003
IZ00139_06.070618.epkg.Z 19174 94 0d8ee47181c7b74454ad0331cea9a57b
These sums should match exactly. The PGP signatures in the
compressed tarball and on this advisory can also be used to verify
the integrity of the various files they correspond to. If the sums
or signatures cannot be confirmed, double check the command results
and the download site address. If those are OK, contact IBM AIX
Security at security-alert@austin.ibm.com and describe the
discrepancy.
C. INTERIM FIX INSTALLATION
These packages use the new Interim Fix Management Solution to install
and manage interim fixes. More information can be found at:
http://www14.software.ibm.com/webapp/set2/sas/f/aix.efixmgmt/home.html
To preview an epkg interim fix installation execute the following
command:
# emgr -e ipkg_name -p # where ipkg_name is the name of the
# interim fix package being previewed.
To install an epkg interim fix package, execute the following command:
# emgr -e ipkg_name -X # where ipkg_name is the name of the
# interim fix package being installed.
The "X" flag will expand any filesystems if required.
VI. WORKAROUNDS
There are a couple of workarounds that may be implemented.
A. OPTION 1
If the program is unnecessary, it may be removed with the following
command:
# rm -f /usr/bin/at
NOTE: To restore this command, the entire bos.rte.cron package must be
reinstalled.
B. OPTION 2
Change the permissions of this command to remove the setuid bit using
the following command:
# chmod 500 /usr/bin/at
NOTE: This will disable functionality of the command for all users
except root.
C. OPTION 3
Customers running AIX 5.3.0 TL06 may install the bos.rte.security
fileset and take advantage of the 'fpm' command to disable the setuid
capabilities of many SUID commands.
The 'at' command is addressed in the high fpm database.
D. OPTION 4
Stack execution disable may be enabled on machines running AIX 5.3 TL05
or later.
VII. OBTAINING FIXES
AIX Version 5 APARs can be downloaded from:
http://www.ibm.com/servers/eserver/support/unixservers/aixfixes.html
Security related Interim Fixes can be downloaded from:
ftp://aix.software.ibm.com/aix/efixes/security
VII. CONTACT INFORMATION
If you would like to receive AIX Security Advisories via email, please
visit:
http://www14.software.ibm.com/webapp/set2/subscriptions/pqvcmjd
Comments regarding the content of this announcement can be directed to:
security-alert@austin.ibm.com
To request the PGP public key that can be used to communicate
securely with the AIX Security Team you can either:
A. Send an email with "get key" in the subject line to:
security-alert@austin.ibm.com
B. Download the key from a PGP Public Key Server. The key ID is:
0x4265D862
Please contact your local IBM AIX support center for any assistance.
eServer is a trademark of International Business Machines Corporation.
IBM, AIX and pSeries are registered trademarks of International Business
Machines Corporation. All other trademarks are property of their
respective holders.
VIII. ACKNOWLEDGMENTS
This vulnerability was discovered internal to IBM as part of its
commitment to secure the AIX operating system.
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