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

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://vulners.com/cve/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://vulners.com/cve/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://vulners.com/cve/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.