IBM SECURITY ADVISORY First Issued: Tue Sep 15 00:52:33 CDT 2026 The most recent version of this document is available here: https://aix.software.ibm.com/aix/efixes/security/python_advisory21.asc Security Bulletin: Multiple vulnerabilities in Python affect AIX =============================================================================== SUMMARY: Vulnerabilities in Python: Improper Input Validation (CVE-2025-13462, CVE-2026-3644), Denial of Service (CVE-2026-15308, CVE-2026-7210, CVE-2026-66046), Use-After-Free / Memory Corruption (CVE-2026-76957), Out-of-Bounds Read / Infinite Loop (CVE-2026-72522, CVE-2026-76641), Insufficient Entropy vulnerability (CVE-2026-76956). Python is used by AIX as part of Ansible node management automation. =============================================================================== VULNERABILITY DETAILS: CVEID: CVE-2025-13462 https://www.cve.org/CVERecord?id=CVE-2025-13462 DESCRIPTION: The "tarfile" module would still apply normalization of AREGTYPE (\x00) blocks to DIRTYPE, even while processing a multi-block member such as GNUTYPE_LONGNAME or GNUTYPE_LONGLINK. This could result in a crafted tar archive being misinterpreted by the tarfile module compared to other implementations. CVSS Base Score: 3.3 CVSS Vector:(CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N) CVEID: CVE-2026-15308 https://www.cve.org/CVERecord?id=CVE-2026-15308 DESCRIPTION: The incremental HTML parser (html.parser.HTMLParser) allows for CPU denial-of-service through repeated unterminated markup declarations when processing uncontrolled data. CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-3644 https://www.cve.org/CVERecord?id=CVE-2026-3644 DESCRIPTION: The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was incomplete. The Morsel.update(), |= operator, and unpickling paths were not patched, allowing control characters to bypass input validation. Additionally, BaseCookie.js_output() lacked the output validation applied to BaseCookie.output(). CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) CVEID: CVE-2026-7210 https://www.cve.org/CVERecord?id=CVE-2026-7210 DESCRIPTION: xml.parsers.expat and xml.etree.ElementTree use insufficient entropy for Expat hash-flooding protection, which allows a crafted XML document to trigger hash flooding. Fully mitigating this vulnerability requires both updating libexpat to 2.8.0 or later and applying this patch. CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-72522 https://www.cve.org/CVERecord?id=CVE-2026-72522 DESCRIPTION: libexpat before 2.8.3 has an out-of-bounds read and resultant infinite loop because low surrogates are treated the same as high surrogates during Unicode processing in the *_toUtf16 functions. CVSS Base Score: 6.2 CVSS Vector:(CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-66046 https://www.cve.org/CVERecord?id=CVE-2026-66046 DESCRIPTION: Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType-defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options. CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-76957 https://www.cve.org/CVERecord?id=CVE-2026-76957 DESCRIPTION: libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412. CVSS Base Score: 7.8 CVSS Vector:(CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) CVEID: CVE-2026-76641 https://www.cve.org/CVERecord?id=CVE-2026-76641 DESCRIPTION: Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046. CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-76956 https://www.cve.org/CVERecord?id=CVE-2026-76956 DESCRIPTION: In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient entropy, which results in being vulnerable to hash flooding attacks, causing a denial of service via crafted XML content. CVSS Base Score: 7.5 CVSS Vector:(CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) AFFECTED PRODUCTS AND VERSIONS: AIX 7.3 VIOS 4.1 The vulnerabilities in the following filesets are being addressed: key_fileset = osrcaix Fileset Lower Level Upper Level KEY ------------------------------------------------------ python3.9.base 3.9.0.0 3.9.24.0 key_w_fs python3.11.base 3.11.0.0 3.11.15.1 key_w_fs 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 To find out whether the affected filesets are installed on your systems, refer to the lslpp command found in the AIX user's guide. Example: lslpp -L | grep -i python3.11.base 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_fix21.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-3.11.16.0.tar.Z key_w_fix VIOS Level Fix (*.Z) KEY ----------------------------------------------- 4.1 python-3.11.16.0.tar.Z key_w_fix To extract the fixes from the tar file: tar xvf python_fix21.tar cd python_fix21.tar 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 --------------------------------------------------------------------------------------------------- fd3ea251840d01c059cd7711740ebba5533a7d575aab121d2cb3ca746f710636 python-3.11.16.0.tar.Z key_w_csum The checksums below were generated using the "openssl dgst -sha512 [filename]" command as the following: openssl dgst -sha512 filename KEY ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ a88dcef0f37c13ea535a7d14759030eb1a52f9dd0ace3f9633932465abf3247cf15c850922afc55bdbd618a2ce3d2c804c2f4e425fe03b44f78c4f3e218d6076 python-3.11.16.0.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_advisory21.asc.sig B. FIX AND INTERIM FIX INSTALLATION To extract the fixes from the tar file: zcat python-3.11.16.0.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. =============================================================================== 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/python_advisory21.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: Security Bulletin: https://www.ibm.com/support/pages/node/7287454 ACKNOWLEDGEMENTS: None. CHANGE HISTORY: First Issued: Tue Sep 15 00:52:33 CDT 2026 =============================================================================== *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.