CVE-2026-81858 is a medium severity (CVSS 5.4) out of bounds read in the File Server host server of IBM i 7.3, 7.4, 7.5 and 7.6. A remote authenticated attacker could cause denial of service and obtain information. IBM provides a PTF for each release: SJ11619, SJ11620, SJ11621 and SJ11622.
What's affected
- IBM i 7.6, 7.5, 7.4 and 7.3 (5770-SS1).
- Fixes: PTF SJ11622 for 7.6, SJ11621 for 7.5, SJ11620 for 7.4 and SJ11619 for 7.3.
- IBM lists no workarounds or mitigations, and says users on unsupported versions should move to a supported, fixed version.
Record severity: CVSS 5.4 (medium), vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L. The weakness class is CWE-125, Out-of-bounds Read.
How to check if you're exposed
On IBM i, run the Display PTF command with the PTF number, for example DSPPTF SJ11621 for release 7.5, to see whether it is installed. The release itself is shown by DSPPTF on product 5770SS1 or in the system values. If the PTF is missing, order and apply it.
What to do now
- List IBM i partitions and their release levels.
- Order the PTF that matches each release from IBM Fix Central.
- Apply the PTF in your normal change window and restart as required by IBM.
- Limit access to host servers such as the File Server to the networks that need it.
- Verify the PTF status after applying.
Why it matters
An out of bounds read (CWE-125) occurs when code reads memory beyond the data it was given. The result can be a crash, which gives denial of service, or exposure of whatever sits next to the buffer, which gives information disclosure. IBM lists both.
The score is medium because the attacker must be authenticated and no code execution is claimed. File Server access is used by many tools, so the number of valid accounts is often large. The record does not mark the CVE as exploited in the wild.
Quick check
Which PTF do I need?
SJ11622 for 7.6, SJ11621 for 7.5, SJ11620 for 7.4, SJ11619 for 7.3.
Is there a workaround?
IBM lists none.
Sources
To see where this and other CVEs sit in your own dependencies, try the free in-browser scan at gold.safeguard.sh/scan.
Last reviewed: 18 October 2026.
