AIX is vulnerable to unauthorized file access and arbitrary code execution due to OpenSSH

IBM SECURITY ADVISORY

First Issued: Wed Aug 23 08:36:37 CDT 2023

The most recent version of this document is available here:
https://aix.software.ibm.com/aix/efixes/security/openssh_advisory15.asc

Security Bulletin: AIX is vulnerable to unauthorized file access and
arbitrary code execution due to OpenSSH (CVE-2023-40371 and
CVE-2023-38408)

===============================================================================

SUMMARY:

Vulnerabilities in AIX's OpenSSH could allow a non-privileged local user
file access outside of those allowed (CVE-2023-40371) or allow a remote
attacker to execute arbitrary code (CVE-2023-38408). OpenSSH is used by
AIX for remote login.

===============================================================================

VULNERABILITY DETAILS:

CVEID: CVE-2023-40371
    https://vulners.com/cve/CVE-2023-40371
DESCRIPTION: IBM AIX's OpenSSH implementation could allow a
    non-privileged local user to access files outside of those allowed
    due to improper access controls.
CVSS Base Score: 6.2
CVSS Temporal Score: See 
    https://exchange.xforce.ibmcloud.com/vulnerabilities/263476
    for the current score
CVSS Environmental Score*: Undefined
CVSS Vector: (CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVEID: CVE-2023-38408
    https://vulners.com/cve/CVE-2023-38408
DESCRIPTION: OpenSSH could allow a remote attacker to execute arbitrary
    code on the system, caused by a flaw in the forwarded ssh-agent. By
    sending specially crafted requests, an attacker could exploit this
    vulnerability to execute arbitrary code on the system.
CVSS Base Score: 8.1
CVSS Temporal Score: See
    https://exchange.xforce.ibmcloud.com/vulnerabilities/261022
    for the current score
CVSS Environmental Score*: Undefined
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:

    AIX 7.2, 7.3
    VIOS 3.1

    The following fileset levels are vulnerable:
    
    key_fileset = aix

    Fileset                 Lower Level  Upper Level  KEY
    ----------------------------------------------------------
    openssh.base.client     8.1.102.0    8.1.102.2106 key_w_fs
    openssh.base.server     8.1.102.0    8.1.102.2106 key_w_fs
    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

    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 AIX and VIOS fixes can be downloaded via https from:

        https://aix.software.ibm.com/aix/efixes/security/openssh_fix15.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       38408m9a.230811.epkg.Z   openssh.base(8.1.102.2106)            key_w_fix
        7.2, 7.3       38408m9b.230811.epkg.Z   openssh.base(8.1.112.2000) 
       key_w_fix
        7.2, 7.3       38408m9c.230811.epkg.Z   openssh.base(9.2.112.2000) 
       key_w_fix

        VIOS Level     Interim Fix (*.Z)             Fileset Name(prereq for installation) KEY
        --------------------------------------------------------------------------------------------
        3.1            38408m9a.230811.epkg.Z   openssh.base(8.1.102.2106) 
       key_w_fix
        3.1            38408m9b.230811.epkg.Z   openssh.base(8.1.112.2000)
       key_w_fix
        3.1            38408m9c.230811.epkg.Z   openssh.base(9.2.112.2000)
       key_w_fix

        To extract the fixes from the tar file:

        tar xvf openssh_fix15.tar
        cd openssh_fix15

        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
        -----------------------------------------------------------------------------------------------------
        77dbc3b40635e16a2f9dba178727bc3fd5e3321c36823c147eb878250e7f6fd0  38408m9a.230811.epkg.Z   key_w_csum
        7a4f56811b3dc179916d5b6de337d40775904f2718480d94dc5a97cd92dc4a25  38408m9b.230811.epkg.Z   key_w_csum
        873adbb99a01500b60729c12bf9a9c18ccf0ac74902cb051d5288eeb4f6ad168  38408m9c.230811.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_advisory15.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:

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

        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:

ftp://ftp.software.ibm.com/systems/power/AIX/systems_p_os_aix_security_pubkey.txt
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_advisory15.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:  http://www.first.org/cvss/user-guide
On-line Calculator v3:
    http://www.first.org/cvss/calculator/3.0

RELATED INFORMATION:

IBM Secure Engineering Web Portal
    http://www.ibm.com/security/secure-engineering/bulletins.html

IBM Product Security Incident Response Blog
    https://www.ibm.com/blogs/psirt/

Security Bulletin: AIX is vulnerable to unauthorized file access and
    arbitrary code execution due to OpenSSH (CVE-2023-40371 and
    CVE-2023-38408)
    https://www.ibm.com/support/pages/node/7028420

ACKNOWLEDGEMENTS:

None.

CHANGE HISTORY:

First Issued: Wed Aug 23 08:36:37 CDT 2023

===============================================================================

*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.