CVE-2026-16943 is a high severity (CVSS 8.2) heap-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 provides cumulative service packs and VIOS fix packs, and the bulletin lists the affected filesets and levels.
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 is an out-of-bounds write. Data goes past the end of a heap buffer and corrupts neighboring memory, which attackers can sometimes shape into code execution. The vector requires high privileges and shows changed scope, with high impact on confidentiality, integrity and availability.
High privileges lower the likelihood, but changed scope means the effect can cross a boundary, which is important on a VIOS that serves other partitions. A compromised administrator account, or a lower step in a chain, may be enough to reach it. Apply the pack and treat it as part of normal hardening.
The weakness class here is CWE-787 (Out-of-bounds Write). The NVD record scores it 8.2, which is high 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 changed, meaning the impact can reach beyond the vulnerable component. 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.
Safeguard's Gold directory tracks this CVE, and reachability analysis helps you decide which affected components matter most for your own software.
Quick check
Does high privilege required make this safe to defer?
It lowers the chance of abuse but does not remove it. Scope is changed in the vector, so the impact can reach beyond the vulnerable component.
Sources
- IBM security bulletin for AIX and VIOS
- Safeguard Gold entry for CVE-2026-16943, which summarizes the NVD record
Last reviewed: 18 October 2026.
