IBM SECURITY ADVISORY First Issued: Thu May 28 14:13:09 CDT 2026 The most recent version of this document is available here: https://aix.software.ibm.com/aix/efixes/security/libxml2_advisory11.asc Security Bulletin: Vulnerabilities in libxml2 (CVE-2026-0989, CVE-2026-0990, CVE-2026-0992, CVE-2026-6732) affect AIX =============================================================================== SUMMARY: Vulnerabilities in libxml2 could cause a denial of service (CVE-2026-0989, CVE-2026-0990, CVE-2026-0992, CVE-2026-6732). AIX uses libxml2 as part of its XML parsing functions. =============================================================================== VULNERABILITY DETAILS: CVEID: CVE-2026-0989 https://www.cve.org/CVERecord?id=CVE-2026-0989 DESCRIPTION: A flaw was identified in the RelaxNG parser of libxml2 related to how external schema inclusions are handled. The parser does not enforce a limit on inclusion depth when resolving nested include directives. Specially crafted or overly complex schemas can cause excessive recursion during parsing. This may lead to stack exhaustion and application crashes, creating a denial-of-service risk. CVSS Base Score: 3.7 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L) CVEID: CVE-2026-0990 https://www.cve.org/CVERecord?id=CVE-2026-0990 DESCRIPTION: A flaw was found in libxml2, an XML parsing library. This uncontrolled recursion vulnerability occurs in the xmlCatalogXMLResolveURI function when an XML catalog contains a delegate URI entry that references itself. A remote attacker could exploit this configuration-dependent issue by providing a specially crafted XML catalog, leading to infinite recursion and call stack exhaustion. This ultimately results in a segmentation fault, causing a Denial of Service (DoS) by crashing affected applications. CVSS Base Score: 5.9 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H) CVEID: CVE-2026-0992 https://www.cve.org/CVERecord?id=CVE-2026-0992 DESCRIPTION: A flaw was found in the libxml2 library. This uncontrolled resource consumption vulnerability occurs when processing XML catalogs that contain repeated nextCatalog elements pointing to the same downstream catalog. A remote attacker can exploit this by supplying crafted catalogs, causing the parser to redundantly traverse catalog chains. This leads to excessive CPU consumption and degrades application availability, resulting in a denial-of-service condition. CVSS Base Score: 2.9 CVSS Environmental Score*: Undefined CVSS Vector: (CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L) CVEID: CVE-2026-6732 https://www.cve.org/CVERecord?id=CVE-2026-6732 DESCRIPTION: A flaw was found in libxml2. This vulnerability occurs when the library processes a specially crafted XML Schema Definition (XSD) validated document that includes an internal entity reference. An attacker could exploit this by providing a malicious document, leading to a type confusion error that causes the application to crash. This results in a denial of service (DoS), making the affected system or application unavailable. CVSS Base Score: 7.5 CVSS Environmental Score*: Undefined 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 7.2, 7.3 VIOS 4.1 The following fileset levels are vulnerable: key_fileset = aix Fileset Lower Level Upper Level KEY --------------------------------------------------------- bos.rte.control 7.2.5.0 7.2.5.206 key_w_fs bos.rte.control 7.3.2.0 7.3.2.3 key_w_fs bos.rte.control 7.3.3.0 7.3.3.2 key_w_fs bos.rte.control 7.3.4.0 7.3.4.0 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 bos.rte.control REMEDIATION: A. APARS IBM has assigned the following APARs to this problem: AIX Level APAR Availability SP KEY ----------------------------------------------------- 7.2.5 IJ58124 ** SP12 key_w_apar 7.3.2 IJ58306 ** N/A key_w_apar 7.3.3 IJ58140 ** SP03 key_w_apar 7.3.4 IJ58122 ** SP01 key_w_apar VIOS Level APAR Availability SP KEY ----------------------------------------------------- 4.1.0 IJ58306 ** N/A key_w_apar 4.1.1 IJ58140 ** 4.1.1.30 key_w_apar 4.1.2 IJ58122 ** 4.1.2.10 key_w_apar Subscribe to the APARs here: https://www.ibm.com/support/pages/apar/[apar number] By subscribing, you will receive periodic email alerting you to the status of the APAR, and a link to download the fix once it becomes available. B. FIXES IBM strongly recommends addressing the vulnerability now. AIX and VIOS fixes are available. The fixes are cumulative and address previously issued AIX/VIOS libxml2 security bulletins with respect to SP and TL. The AIX and VIOS fixes can be downloaded via https from: https://aix.software.ibm.com/aix/efixes/security/libxml2_fix11.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. AIX Level Interim Fix (*.Z) KEY ---------------------------------------------- 7.2.5.9 IJ58124mBa.260527.epkg.Z key_w_fix 7.2.5.10 IJ58124mBa.260527.epkg.Z key_w_fix 7.2.5.11 IJ58124mBa.260527.epkg.Z key_w_fix 7.3.2.2 IJ58306m4a.260527.epkg.Z key_w_fix 7.3.2.3 IJ58306m4a.260527.epkg.Z key_w_fix 7.3.2.4 IJ58306m4a.260527.epkg.Z key_w_fix 7.3.3.0 IJ58140m2a.260527.epkg.Z key_w_fix 7.3.3.1 IJ58140m2a.260527.epkg.Z key_w_fix 7.3.3.2 IJ58140m2a.260527.epkg.Z key_w_fix 7.3.4.0 IJ58122m0a.260528.epkg.Z key_w_fix Please note that the above table refers to AIX TL/SP level as opposed to fileset level, i.e., 7.3.2.3 is AIX 7300-02-03. Please reference the Affected Products and Version section above for help with checking installed fileset levels. VIOS Level Interim Fix (*.Z) KEY ----------------------------------------------- 4.1.0.21 IJ58306m4a.260527.epkg.Z key_w_fix 4.1.0.30 IJ58306m4a.260527.epkg.Z key_w_fix 4.1.0.40 IJ58306m4a.260527.epkg.Z key_w_fix 4.1.1.0 IJ58140m2a.260527.epkg.Z key_w_fix 4.1.1.10 IJ58140m2a.260527.epkg.Z key_w_fix 4.1.1.20 IJ58140m2a.260527.epkg.Z key_w_fix 4.1.2.0 IJ58122m0a.260528.epkg.Z key_w_fix To extract the fixes from the tar file: tar xvf libxml2_fix11.tar cd libxml2_fix11 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 ----------------------------------------------------------------------------------------------------- 244adec9058fd009f6f91f9e52fd0815d75e684e11b5e6fa35f70bc06eb7b651 IJ58122m0a.260528.epkg.Z key_w_csum 75f0b7f755fa818a52ba6c6d5b86c9c9cfb358f8cf26ac85926ddfb527fc151a IJ58124mBa.260527.epkg.Z key_w_csum 1f1fa83837dc7ed7f28239255708c16ae50bc884ca2e725cb2ff3b96df7fd1df IJ58140m2a.260527.epkg.Z key_w_csum 30e509ce62fd38b3d3ed6c3c9b1dbdf71cdaf764da123ab7eea6d17e93b204d2 IJ58306m4a.260527.epkg.Z key_w_csum The checksums below were generated using the "openssl dgst -sha512 [filename]" command as the following: openssl dgst -sha512 filename ------------------------------------------------------------------------------------------------------------------------------------------------------------------------ c676b700e9b85edc446b58473319ab192fa92332f96ca1d148c3f66e358d319450d464d36807765aca6160e51330b2786227e95e8726dd905fe2329d9bbf4512 IJ58122m0a.260528.epkg.Z key_4K_w_csum be3f32432ef9ac67c92425d6dc1f8e41103d9145bffb9a3a7023acf1b4dbb5b151547be8044a731fccd162a86c72bdfc0d33628e06a9d6a2b3cf38e610f7c500 IJ58124mBa.260527.epkg.Z key_4K_w_csum 3799b85305d9f6bc8aad1942aa179bd0f05fee95968dbbb5fc2a1d4dc8fa4306a336742e320450f537e86435856784227571a8568543b305a2c4850f9853490b IJ58140m2a.260527.epkg.Z key_4K_w_csum 4d527bc740623195f545ee0fa3363eff399748d4db325962fb37e3f7c5ee85e1da724cdadbb11bffb0bbaf470b81ee15128dc48a04048514b59a73d0a5e2d553 IJ58306m4a.260527.epkg.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 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/libxml2_advisory11.asc.sig C. 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/libxml2_advisory11.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: https://www.ibm.com/support/pages/node/7274376 ACKNOWLEDGEMENTS: None. CHANGE HISTORY: First Issued: Thu May 28 14:13:09 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.