Summary

Vulnerabilities in AIX’s OpenSSH could allow a remote attacker to launch a machine-in-the-middle attack (CVE-2023-48795) and execute arbitrary commands (CVE-2023-51385), and could allow a local authenticated attacker to obtain sensitive information (CVE-2023-51384). OpenSSH is used by AIX for remote login.

Vulnerability Details

CVEID:CVE-2023-48795
**DESCRIPTION:**OpenSSH is vulnerable to a machine-in-the-middle attack, caused by a flaw in the extension negotiation process in the SSH transport protocol when used with certain OpenSSH extensions. A remote attacker could exploit this vulnerability to launch a machine-in-the-middle attack and strip an arbitrary number of messages after the initial key exchange, breaking SSH extension negotiation and downgrading the client connection security.
CVSS Base score: 5.9
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/275282 for the current score.
CVSS Vector: (CVSS:3.0/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N)

CVEID:CVE-2023-51385
**DESCRIPTION:**OpenSSH could allow a remote attacker to execute arbitrary commands on the system, caused by improper validation of shell metacharacters. By sending a specially crafted request using expansion tokens, an attacker could exploit this vulnerability to execute arbitrary commands on the system.
CVSS Base score: 9.8
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/275402 for the current score.
CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

CVEID:CVE-2023-51384
**DESCRIPTION:**OpenSSH could allow a local authenticated attacker to obtain sensitive information, caused by a flaw when specifying destination constraints while adding PKCS#11-hosted private keys. By sending a specially crafted request, an attacker could exploit this vulnerability to obtain sensitive information, and use this information to launch further attacks against the affected system.
CVSS Base score: 4.4
CVSS Temporal Score: See: https://exchange.xforce.ibmcloud.com/vulnerabilities/275400 for the current score.
CVSS Vector: (CVSS:3.0/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:N/A:N)

Affected Products and Versions

The following fileset levels are vulnerable:

Note:

A. OpenSSH 8.1.102.xxxx is out-of-support. Users are advised to upgrade to OpenSSH 8.1.112.xxxx or 9.2.112.xxxx.

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

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

C. CVE-2023-51384 only applies to AIX OpenSSH 9.2.

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 openssh.base.client

Remediation/Fixes

A. FIXES

IBM strongly recommends addressing the vulnerability now.

AIX and VIOS fixes are available. The fixes are cumulative and address previously issued AIX OpenSSH security bulletins:

<https://aix.software.ibm.com/aix/efixes/security/openssh_advisory15.asc&gt;

<https://www.ibm.com/support/pages/node/7028420&gt;

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

<https://aix.software.ibm.com/aix/efixes/security/openssh_fix16.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_fix16.tar

cd openssh_fix16

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_advisory16.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