# CVE-2026-31611

> Vulnerability · severity: **HIGH** (CVSS 8.6).

## Description

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: require 3 sub-authorities before reading sub_auth[2]

parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on
match reads sid.sub_auth[2] as the file mode.  If sid_unix_NFS_mode is
the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares
only min(num_subauth, 2) sub-authorities so a client SID with
num_subauth = 2 and sub_auth = {88, 3} will match.

If num_subauth = 2 and the ACE is placed at the very end of the security
descriptor, sub_auth[2] will be  4 bytes past end_of_acl.  The
out-of-band bytes will then be masked to the low 9 bits and applied as
the file's POSIX mode, probably not something that is good to have
happen.

Fix this up by forcing the SID to actually carry a third sub-authority
before reading it at all.

## Key facts

- **CVE ID:** CVE-2026-31611
- **Published:** 2026-04-24
- **CVSS severity:** HIGH
- **CVSS base score:** 8.6
- **CWE codes:** NVD-CWE-noinfo

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31611

## Citation

> AI Analytics. CVE-2026-31611. Retrieved 2026-08-17 from https://api.ai-analytics.org/cve/CVE-2026-31611. Derived from NIST NVD. Licensed CC0.

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