Summary

Vulnerability in AIX’s OpenSSH could allow a remote attacker to execute arbitrary code (CVE-2024-6387). OpenSSH is used by AIX for remote login.

Vulnerability Details

CVEID:CVE-2024-6387
**DESCRIPTION:**OpenSSH could allow a remote attacker to execute arbitrary code on the system, caused by a signal handler race condition. By sending a specially crafted request, an attacker could exploit this vulnerability to execute arbitrary code with root privileges on glibc-based Linux systems.
CVSS Base score: 8.1
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/296064 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H)

Affected Products and Versions

The following fileset levels are vulnerable:

Note:

A. Latest level of OpenSSH fileset is available from the Web Download site:

<https://www.ibm.com/resources/mrs/assets?source=aixbp&gt;

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 openssh.base.client

Remediation/Fixes

A. FIXES

IBM strongly recommends addressing the vulnerability now.

AIX and VIOS fixes are available. The AIX and VIOS fixes can be downloaded via https from:

<https://aix.software.ibm.com/aix/efixes/security/openssh_fix17.tar&gt;

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.

Note that the tar file contains Interim fixes that are based on OpenSSH version, and AIX OpenSSH 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 from:

<https://www.ibm.com/resources/mrs/assets?source=aixbp&gt;

To extract the fixes from the tar file:

tar xvf openssh_fix17.tar

cd openssh_fix17

Verify you have retrieved the fixes intact:

The checksums below were generated using the “openssl dgst -sha256 [filename]” 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 Support at <http://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:

<https://aix.software.ibm.com/aix/efixes/security/openssh_advisory17.asc.sig&gt;

B. 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:

<https://www.ibm.com/support/pages/managing-interim-fixes-aix&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