IBM SECURITY ADVISORY First Issued: Wed Feb 28 12:58:51 CST 2024 The most recent version of this document is available here: https://aix.software.ibm.com/aix/efixes/security/openssh_advisory16.asc Security Bulletin: AIX is vulnerable to a machine-in-the-middle attack (CVE-2023-48795), arbitrary command execution (CVE-2023-51385), and information disclosure (CVE-2023-51384) due to OpenSSH =============================================================================== 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 https://cve.mitre.org/cgi-bin/cvename.cgi?name=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 Environmental Score*: Undefined 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 https://cve.mitre.org/cgi-bin/cvename.cgi?name=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 Environmental Score*: Undefined 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 https://cve.mitre.org/cgi-bin/cvename.cgi?name=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 Environmental Score*: Undefined 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: AIX 7.2, 7.3 VIOS 3.1, 4.1 The following fileset levels are vulnerable: key_fileset = aix Fileset Lower Level Upper Level KEY ---------------------------------------------------------- openssh.base.client 8.1.112.0 8.1.112.2000 key_w_fs openssh.base.server 8.1.112.0 8.1.112.2000 key_w_fs openssh.base.client 9.2.112.0 9.2.112.2000 key_w_fs openssh.base.server 9.2.112.0 9.2.112.2000 key_w_fs 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 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: 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 https://www.ibm.com/support/pages/node/7028420 The AIX and VIOS fixes can be downloaded via https from: https://aix.software.ibm.com/aix/efixes/security/openssh_fix16.tar 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 AIX Level Interim Fix (*.Z) Fileset Name(prereq for installation) KEY --------------------------------------------------------------------------------------- 7.2, 7.3 81112ma.240224.epkg.Z openssh.base(8.1.112.2000) key_w_fix 7.2, 7.3 92112ma.240223.epkg.Z openssh.base(9.2.112.2000) key_w_fix VIOS Level Interim Fix (*.Z) Fileset Name(prereq for installation) KEY -------------------------------------------------------------------------------------------- 3.1, 4.1 81112ma.240224.epkg.Z openssh.base(8.1.112.2000) key_w_fix 3.1, 4.1 92112ma.240223.epkg.Z openssh.base(9.2.112.2000) key_w_fix 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: openssl dgst -sha256 filename KEY ----------------------------------------------------------------------------------------------------- fced2634fa3c2cf541f6fb30653cc7bec7f9828317b7e4de9745d9b37ab20ebd 81112ma.240224.epkg.Z key_w_csum bd2ea6ccc957d17b5821e77b75122024f6e22f22e681c1a0adde8712eae13012 92112ma.240223.epkg.Z key_w_csum 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: https://aix.software.ibm.com/aix/efixes/security/openssh_advisory16.asc.sig 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 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. =============================================================================== CONTACT US: Note: Keywords labeled as KEY in this document are used for parsing purposes. If you would like to receive AIX Security Advisories via email, please visit "My Notifications": http://www.ibm.com/support/mynotifications Contact IBM Support for questions related to this announcement: https://ibm.com/support/ For information on how to securely verify AIX security bulletins and fixes: https://www.ibm.com/support/pages/node/6985269 To obtain the OpenSSL public key that can be used to verify the signed advisories and ifixes: Download the key from our web page: https://aix.software.ibm.com/aix/efixes/security/systems_p_os_aix_security_pubkey.txt To verify the AIX/VIOS security bulletin: Published advisory OpenSSL signature file location: https://aix.software.ibm.com/aix/efixes/security/openssh_advisory16.asc.sig openssl dgst -sha256 -verify [pubkey_file] -signature [advisory_file].sig [advisory_file] Please contact your local IBM AIX support center for any assistance. REFERENCES: Complete CVSS v3 Guide: https://www.first.org/cvss/user-guide On-line Calculator v3: https://www.first.org/cvss/calculator/3.0 RELATED INFORMATION: IBM Secure Engineering Web Portal https://www.ibm.com/support/pages/ibm-security-vulnerability-management IBM Product Security Incident Response Blog https://www.ibm.com/blogs/psirt/ Security Bulletin: AIX is vulnerable to a machine-in-the-middle attack (CVE-2023-48795), arbitrary command execution (CVE-2023-51385), and information disclosure (CVE-2023-51384) due to OpenSSH https://www.ibm.com/support/pages/node/7125640 ACKNOWLEDGEMENTS: None. CHANGE HISTORY: First Issued: Wed Feb 28 12:58:51 CST 2024 =============================================================================== *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.