Security Bulletin
Summary
Use after free and heap buffer overflow may casue denial of service.
Vulnerability Details
CVEID: CVE-2026-56131
DESCRIPTION: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in cases of a policy violation. Thus, a use-after-free can occur (similar to the CVE-2026-50219 situation).
CWE: CWE-416: Use After Free
CVSS Source: cve@mitre.org
CVSS Base score: 4.9
CVSS Vector: (CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L)
CVEID: CVE-2026-56132
DESCRIPTION: In libexpat before 2.8.2, there is a heap-based buffer overflow in doProlog in xmlparse.c because scaffold backing array reallocation is mishandled when there is data-structure sharing across parsers.
CWE: CWE-821: Incorrect Synchronization
CVSS Source: NVD
CVSS Base score: 6.9
CVSS Vector: (CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L)
Affected Products and Versions
AFFECTED PRODUCTS AND VERSIONS:
| Affected Product(s) | Version(s) |
| AIX | 7.3 |
| VIOS | 4.1 |
The vulnerabilities in the following filesets are being addressed:
key_fileset = osrcaix
| Fileset | Lower Level | Upper Level |
| python3.9.base | 3.9.0.0 | 3.9.24.0 |
| python3.11.base | 3.11.0.0 | 3.11.15.0 |
Note:
A. Python 3.9 is out-of-support. Considering long term support, it is advised to upgrade to Python 3.11.
B. Latest level of Python fileset is available from the web download site:
https://www.ibm.com/resources/mrs/assets?source=aixbp
Remediation/Fixes
REMEDIATION:
A. FIXES
IBM strongly recommends addressing the vulnerability now.
The fixes can be downloaded via https from:
https://aix.software.ibm.com/aix/efixes/security/python_fix20.tar
The links above are 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.
AIX Level Fix (*.Z) KEY
-----------------------------------------------
7.3 python-3.11.15.1.tar.Z key_w_fix
VIOS Level Fix (*.Z) KEY
-----------------------------------------------
4.1 python-3.11.15.1.tar.Z key_w_fix
To extract the fixes from the tar file:
tar xvf python_fix20.tar
cd python_fix20
Verify you have retrieved the fixes intact:
The checksums below were generated using the
"openssl dgst -sha256 [file]" command as the following:
openssl dgst -sha256 filename KEY
---------------------------------------------------------------------------------------------------
1c8bf8003e57165d2b46f2ba2eea35c03f5095dc95dbb49882e700d5f4edb1e0 python-3.11.15.1.tar.Z key_w_csum
The checksums below were generated using the
"openssl dgst -sha512 [filename]" command as the following:
openssl dgst -sha512 filename
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
f08361d4d8b09c92e3b478a90c6f699dfa05f1b045ba2b6d0b9faa28aa9a7a0e1339c58c75f8346b17f15a4802d6b99b0804ba932b6207517cd7a13ec7a86b06 python-3.11.15.1.tar.Z key_4K_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 AIX Support at
https://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/python_advisory20.asc.sig
B. FIX AND INTERIM FIX INSTALLATION
To extract the fixes from the tar file:
zcat python-3.11.15.1.tar.Z | tar xvf -
IMPORTANT: 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 the fix installation:
installp -apYd . python3.11.base
To install the fix package:
installp -aXYd . python3.11.base
Workarounds and Mitigations
None
Get Notified about Future Security Bulletins
References
Acknowledgement
Change History
15 Jul 2026: Initial Publication
*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. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.
Document Location
Worldwide
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Document Information
Modified date:
15 July 2026
Initial Publish date:
15 July 2026
UID
ibm17280107