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Security Bulletin: Vulnerability in ksh affects AIX (CVE-2021-29741)

Security Bulletin


Summary

There is a vulnerability in Korn Shell (ksh) that affects AIX.

Vulnerability Details

CVEID:   CVE-2021-29741
DESCRIPTION:   IBM AIX 7.1, 7.2, and VIOS 3.1 could allow a local user to exploit a vulnerability in Korn Shell (ksh) to gain root privileges. IBM X-Force ID: 201478.
CVSS Base score: 8.4
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/201478 for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Affected Products and Versions

Affected Product(s) Version(s)
AIX 7.1
AIX 7.2
VIOS 3.1

The vulnerabilities in the following filesets are being addressed:

Fileset Lower Level Upper Level
bos.rte.shell 7.1.5.30 7.1.5.36
bos.rte.shell 7.2.3.0 7.2.3.20
bos.rte.shell 7.2.4.0 7.2.4.3
bos.rte.shell 7.2.5.0 7.2.5.2
To find out whether the affected filesets are installed on your systems, refer to the lslpp command found in AIX user's guide.
Example:  lslpp -L | grep -i bos.rte.shell

Remediation/Fixes

A. APARS
            
IBM has assigned the following APARs to this problem:
AIX Level APAR SP
7.1.5 IJ31606 SP09
7.2.3 IJ32285 N/A
7.2.4 IJ31614 SP05
7.2.5 IJ31545 SP03

VIOS Level APAR SP
3.1.0 IJ32285 N/A
3.1.1 IJ31614 3.1.1.50
3.1.2 IJ30557 3.1.2.30

Subscribe to the APARs here:
https://www.ibm.com/support/pages/apar/IJ30557
https://www.ibm.com/support/pages/apar/IJ31545
https://www.ibm.com/support/pages/apar/IJ31606
https://www.ibm.com/support/pages/apar/IJ31614
https://www.ibm.com/support/pages/apar/IJ32285

By subscribing, you will receive periodic email alerting you to the status of the APAR, and a link to download the fix once it becomes available.

B. FIXES
AIX and VIOS fixes are available.
The AIX and VIOS fixes can be downloaded via ftp or http from:
The link above is to a tar file containing this signed advisory, fix packages, and OpenSSL signatures for each package. The fixes below include prerequisite checking. This will enforce the correct mapping between the fixes and AIX Technology Levels.
AIX Level Interim Fix
7.1.5.6 IJ31606s6a.210628.epkg.Z
7.1.5.7 IJ31606s7a.210628.epkg.Z
7.1.5.8 IJ31606s7a.210628.epkg.Z
7.2.3.5 IJ32285s4a.210628.epkg.Z
7.2.3.6 IJ32285s4a.210628.epkg.Z
7.2.3.7 IJ32285s4a.210628.epkg.Z
7.2.4.2 IJ31614s1a.210427.epkg.Z
7.2.4.3 IJ31614s1a.210427.epkg.Z
7.2.4.4 IJ31614s1a.210427.epkg.Z
7.2.5.0 IJ30557s2a.210427.epkg.Z
7.2.5.1 IJ30557s2a.210427.epkg.Z
7.2.5.2 IJ30557s2a.210427.epkg.Z

Please note that the above table refers to AIX TL/SP level as opposed to fileset level, i.e., 7.2.3.5 is AIX 7200-03-05.
Please reference the Affected Products and Version section above for help with checking installed fileset levels.
VIOS Level Interim Fix
3.1.0.40 IJ32285s4a.210628.epkg.Z
3.1.0.50 IJ32285s4a.210628.epkg.Z
3.1.0.60 IJ32285s4a.210628.epkg.Z
3.1.1.20 IJ31614s1a.210427.epkg.Z
3.1.1.21 IJ31614s1a.210427.epkg.Z
3.1.1.25 IJ31614s1a.210427.epkg.Z
3.1.1.30 IJ31614s1a.210427.epkg.Z
3.1.1.40 IJ31614s1a.210427.epkg.Z
3.1.2.0 IJ30557s2a.210427.epkg.Z
3.1.2.10 IJ30557s2a.210427.epkg.Z
3.1.2.20 IJ30557s2a.210427.epkg.Z
3.1.2.21 IJ30557s2a.210427.epkg.Z

To extract the fixes from the tar file:
tar xvf ksh_fix.tar
cd ksh_fix
Verify you have retrieved the fixes intact:
The checksums below were generated using the "openssl dgst -sha256 [filename]" command as the following:
openssl dgst -sha256 filename
937c07cf9e42f7d0a5f2c4d3deee84da46bef49c174ffeb8d01f010d5aacd11e IJ30557s2a.210427.epkg.Z
764dfe4293c05298cc7325d57106850382a341127bbd9a0fefb469ff42706aa8 IJ31606s6a.210628.epkg.Z
de26cdab804af608be1392c53346037d7cd2de91cf67acab5d0e9d3ca988763a IJ31606s7a.210628.epkg.Z
2e9acbabe8632065096fe4e1ea6387af23cb495bff8e744c91205ba280bfa855 IJ31614s1a.210427.epkg.Z
6e7efc563989dc3a504ae9626b36053d2d58a6f3242660830c5019d67953dfa7 IJ32285s4a.210628.epkg.Z

These sums should match exactly. The OpenSSL signatures in the tar file and on this advisory can also be used to verify the integrity of the fixes.  If the sums or signatures cannot be confirmed, contact IBM Support at http://ibm.com/support/ and describe the discrepancy.         
openssl dgst -sha256 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file]
openssl dgst -sha256 -verify [pubkey_file] -signature [ifix_file].sig [ifix_file]
Published advisory OpenSSL signature file location:
C. FIX AND INTERIM FIX INSTALLATION
If possible, it is recommended that a mksysb backup of the system be created. Verify it is both bootable and readable before proceeding.
To preview a fix installation:
installp -a -d fix_name -p all  # where fix_name is the name of the
                                            # fix package being previewed.
To install a fix package:
installp -a -d fix_name -X all  # where fix_name is the name of the
                                            # fix package being installed.
Interim fixes have had limited functional and regression testing but not the full regression testing that takes place for Service Packs; however, IBM does fully support them.
Interim fix management documentation can be found at:
To preview an interim fix installation:
emgr -e ipkg_name -p         # where ipkg_name is the name of the
                                         # interim fix package being previewed.
To install an interim fix package:
emgr -e ipkg_name -X         # where ipkg_name is the name of the
                                         # interim fix package being installed.

Workarounds and Mitigations

None

Get Notified about Future Security Bulletins

References

Off

Acknowledgement

Change History

11 Aug 2021: Corrected the AIX 7.1 TL5 affected fileset levels
30 Jul 2021: Initial Publication

*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.

Disclaimer

According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY.

Document Location

Worldwide

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Document Information

Modified date:
12 October 2021

UID

ibm16477018