CVE-2026-16944 is a medium severity (CVSS 6.7) stack-based buffer overflow in IBM AIX 7.2 and 7.3 and PowerVM VIOS 4.1. A local attacker with high privileges could execute arbitrary code. IBM fixes it in cumulative service packs and VIOS fix packs.
What's affected
IBM AIX 7.2 and 7.3, and IBM PowerVM VIOS 4.1. IBM's bulletin lists the affected fileset as bos.mp64 at these levels:
- AIX 7.2.5: 7.2.5.0 through 7.2.5.212
- AIX 7.3.2: 7.3.2.0 through 7.3.2.5
- AIX 7.3.3: 7.3.3.0 through 7.3.3.2
- AIX 7.3.4: 7.3.4.0 through 7.3.4.1
The same bulletin covers a large group of AIX and VIOS issues, and one set of fixes addresses all of them. Per the bulletin, the remediation levels are AIX 7.2 TL05 SP13, AIX 7.3 TL02 SP5, AIX 7.3 TL03 SP3 and AIX 7.3 TL04 SP2, and VIOS fix packs 4.1.0.50, 4.1.1.30 and 4.1.2.20. The service packs and fix packs are cumulative.
How to check if you're exposed
Run these on each AIX LPAR and on each VIOS:
oslevel -s
lslpp -L | grep -i bos.mp64
On a VIOS, log in as padmin and run ioslevel. Compare the bos.mp64 level against the ranges above. If the fileset is at or below the upper level for its release, the system is in scope. You can also check for the APAR that matches your release with instfix -ik IJ59565 (use IJ59566 for 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 and VIOS system and record
oslevel -soriosleveloutput. - Compare each against the bos.mp64 ranges in IBM's bulletin 7283858.
- Download the matching service pack or VIOS fix pack from Fix Central. Plan for an LPAR reboot, or use AIX Live Update where it suits you.
- If you patch through NIM with nimsh secure, read the IBM note linked in the bulletin first, because the protocol between master and client changed.
- On VIOS 4.1.0 and 4.1.1, follow the post-update Postgres15 migration steps IBM links in the bulletin.
- Re-run the version check and record the new level.
Why it matters
CWE-787 covers out-of-bounds writes, and this one lands on the stack, where overwritten data can include return addresses. The record says code execution is possible for a local attacker. The vector needs high privileges and leaves scope unchanged, which is why the score is medium at 6.7.
A medium score is no reason to skip the pack. Because the fix pack is cumulative, applying it for the higher rated issues in the same bulletin removes this one too. Treat the whole bulletin as one patch event.
The weakness class here is CWE-787 (Out-of-bounds Write). The NVD record scores it 6.7, which is medium severity. IBM's bulletin gives the same score. The CVSS vector reads attack vector with local access, low attack complexity, high privileges required, no user interaction. Scope is unchanged. Impact on confidentiality, integrity and availability is rated high, high and high. The record's KEV flag is false, so this CVE is not in CISA's Known Exploited Vulnerabilities catalog, and the advisory I fetched does not report exploitation.
Try it yourself
A free in-browser dependency scan at gold.safeguard.sh/scan shows which of your components match known CVEs. The demo below walks through the idea.
Click through it at your own pace, or open it full screen.
Quick check
Why is this scored lower than the heap overflow?
The vector shows scope unchanged, unlike the heap overflow, which shows changed scope. Both need high privileges.
Sources
- IBM security bulletin for AIX and VIOS
- Safeguard Gold entry for CVE-2026-16944, which summarizes the NVD record
Last reviewed: 18 October 2026.
