CVE-2026-17138 is a high severity (CVSS 8.1) stack-based buffer overflow in IBM AIX 7.2 and 7.3 and PowerVM VIOS 4.1. A remote attacker could execute arbitrary code. IBM published cumulative service packs and fix packs, so update each system to the remediation level in the bulletin.
What's affected
IBM AIX 7.2 and 7.3, and IBM PowerVM VIOS 4.1. IBM's bulletin is a shared one that lists many AIX and VIOS vulnerabilities, and its change history shows an initial publication on 15 August 2026. The affected fileset is bos.mp64 at these levels:
- AIX 7.2.5: 7.2.5.0 to 7.2.5.212
- AIX 7.3.2: 7.3.2.0 to 7.3.2.5
- AIX 7.3.3: 7.3.3.0 to 7.3.3.2
- AIX 7.3.4: 7.3.4.0 to 7.3.4.1
IBM's remediation levels are AIX 7.2 TL05 SP13, 7.3 TL02 SP5, 7.3 TL03 SP3 and 7.3 TL04 SP2, and VIOS fix packs 4.1.0.50, 4.1.1.30 and 4.1.2.20. These service packs are cumulative. IBM lists no workaround or mitigation.
How to check if you're exposed
Check the AIX level and the affected fileset on each LPAR.
oslevel -s
lslpp -L | grep -i bos.mp64
On a VIOS, run ioslevel as padmin. If the bos.mp64 level falls in one of the ranges above, the system is affected. IBM also assigns APARs: IJ59566 for AIX 7.2.5, IJ59565 for 7.3.2, IJ59564 for 7.3.3 and IJ59563 for 7.3.4.
What to do now
- List every AIX LPAR and VIOS, with its technology level and service pack.
- Download the service pack or fix pack for your level from IBM Fix Central.
- Plan the LPAR reboot, or use Live Update on AIX where it fits, because IBM says a reboot is needed to complete the update.
- Read IBM's notes on nimsh secure and, for VIOS 4.1.0 and 4.1.1, the post-update steps for the Postgres15 migration.
- Recheck
oslevel -safter the update and record it.
Why it matters
The weakness is CWE-121 (Stack-based Buffer Overflow). A stack overflow writes past a local buffer into nearby stack memory, which can change where the program goes next. IBM says a remote attacker could use this to execute arbitrary code.
The vector marks complexity as high, with no privileges and no user interaction, and high impact across confidentiality, integrity and availability. The same IBM bulletin lists several other memory errors, so one cumulative update closes many of them together. CISA does not list this CVE as known exploited.
Quick check
Is there a workaround?
IBM lists none. The fix is the service pack or fix pack.
Sources
Last reviewed: 19 October 2026.
