CVE-2026-16853 is a medium severity (CVSS 6.5) out-of-bounds read in IBM i 7.3, 7.4, 7.5 and 7.6. A remote attacker could obtain sensitive information, with no account needed. IBM provides a PTF for each release under licensed program 5770-999, and the bulletin lists the numbers.
What's affected
IBM i 7.6, 7.5, 7.4 and 7.3, per IBM's bulletin and the NVD record. IBM lists these PTFs for 5770-999:
- IBM i 7.6: MJ10939
- IBM i 7.5: MJ10938
- IBM i 7.4: MJ10937
- IBM i 7.3: MJ10936
IBM says to address the issue now and recommends that users of unsupported IBM i releases move to a supported, fixed version.
How to check if you're exposed
IBM i 7.3 through 7.6 are all in scope, so every supported and recently supported release needs a look. On each partition, confirm the installed release and then check whether the PTF for your release is loaded. From a command line:
DSPPTF LICPGM(5770999)
Look for the PTF number listed for your release in the table above, with a status of Applied or Permanently applied. You can also use option 10 of GO LICPGM to confirm the release. Do this on every LPAR, including test and recovery systems, because they are often patched last.
What to do now
- List every IBM i partition and its release, including test and disaster recovery systems.
- Find the PTF for your release in the table above, and order it from IBM Fix Central or through your usual PTF process.
- Apply the PTF and restart as the PTF cover letter requires.
- Check the PTF status with DSPPTF and record it.
- Limit access to IBM i network services to the hosts and users that need them.
Why it matters
CWE-125 is an out-of-bounds read. The code reads outside the buffer it should be limited to, and the extra bytes can contain data from other parts of memory. The vector shows network access, no privileges and no interaction, with low confidentiality and low availability impact.
Network reachable and unauthenticated is the part that deserves attention. The same bulletin includes CVE-2026-16868, rated 8.1, so the PTF has more value than this single score suggests.
The weakness class here is CWE-125 (Out-of-bounds Read). The NVD record scores it 6.5, which is medium severity. IBM's bulletin gives the same score. The CVSS vector reads attack vector over the network, low attack complexity, no privileges required, no user interaction. Scope is unchanged. Impact on confidentiality, integrity and availability is rated low, none and low. 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
Is the same PTF used for the other CVEs in the bulletin?
Yes, IBM lists one PTF per release for the bulletin. Confirm in the bulletin which licensed program and PTF set apply to your system.
Sources
- IBM security bulletin
- Safeguard Gold entry for CVE-2026-16853, which summarizes the NVD record
Last reviewed: 18 October 2026.
