Summary

There is a vulnerability in OpenSSH used by AIX.

Vulnerability Details

CVEID:CVE-2021-41617
**DESCRIPTION:**OpenSSH could allow a local attacker to gain elevated privileges on the system, caused by an error in sshd when certain non-default configurations are used. By executing an AuthorizedKeysCommand or AuthorizedPrincipalsCommand, where a AuthorizedKeysCommandUser or AuthorizedPrincipalsCommandUser directive has been set to run the command as a non-root user, an attacker could exploit this vulnerability to gain privileges associated with group memberships of the sshd process.
CVSS Base score: 7.4
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/210062 for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H)

Affected Products and Versions

The following fileset levels are vulnerable:

8.1.102.2104

Note:
A. 6.0, 7.1, 7.5 OpenSSH versions are out-of-support. Refer to AIX release notes for supported OpenSSH versions. Customers are advised to upgrade to currently supported OpenSSH 8.1 version.

B. Latest level of OpenSSH fileset is available from the web download site:
https://www.ibm.com/resources/mrs/assets?source=aixbp&S_PKG=openssh

To determine if your system is vulnerable, execute the following commands:

lslpp -L | grep -i openssh.base.client

lslpp -L | grep -i openssh.base.server

Remediation/Fixes

A. FIXES

The fixes can be downloaded via ftp or http from:

ftp://aix.software.ibm.com/aix/efixes/security/openssh_fix14.tar

<http://aix.software.ibm.com/aix/efixes/security/openssh_fix14.tar&gt;

<https://aix.software.ibm.com/aix/efixes/security/openssh_fix14.tar&gt;

The links above are 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.

Note that the tar file contains Interim fixes that are based on OpenSSL version, and AIX OpenSSL fixes are cumulative.

You must be on the ‘prereq for installation’ level before applying the interim fix. This may require installing a new level(prereq version) first.

To extract the fixes from the tar file:

tar xvf openssh_fix14.tar

cd openssh_fix14

Verify you have retrieved the fixes intact:

The checksums below were generated using the “openssl dgst -sha256 [file]” command as the following:

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 AIX Support at <https://ibm.com/support/&gt; 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:

<http://aix.software.ibm.com/aix/efixes/security/openssh_advisory14.asc.sig&gt;

<https://aix.software.ibm.com/aix/efixes/security/openssh_advisory14.asc.sig&gt;

ftp://aix.software.ibm.com/aix/efixes/security/openssh_advisory14.asc.sig

B. FIX AND INTERIM FIX INSTALLATION

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:

<http://www14.software.ibm.com/webapp/set2/sas/f/aix.efixmgmt/home.html&gt;

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