CVE-2026-43350: smb: client: require a full NFS mode SID before reading mode bits

Severity: high (CVSS 7.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-08 · updated 2026-10-19
Weakness: CWE-125

Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: require a full NFS mode SID before reading mode bits parse_dacl() treats an ACE SID matching sid_unix_NFS_mode as an NFS mode SID and reads sid.sub_auth[2] to recover the mode bits. That assumes the ACE carries three subauthorities, but compare_sids() only compares min(a, b) subauthorities. A malicious server can return an ACE with num_subauth = 2 and sub_auth[] = {88, 3}, which still matches sid_unix_NFS_mode and then drives the sub_auth[2] read four bytes past the end of the ACE. Require num_subauth >= 3 before treating the ACE as an NFS mode SID. This keeps the fix local to the special-SID mode path without changing compare_sids() semantics for the rest of cifsacl.

Affected products

Linux kernel: from 5.4 before 6.6.136; from 6.7 before 6.12.84; from 6.13 before 6.18.25; from 6.19 before 7.0.2 — fixed in 6.12.84, 6.18.25, 6.6.136, 7.0.2

How to fix

Upgrade to a fixed version: Linux kernel 6.12.84, 6.18.25, 6.6.136, 7.0.2. Check the vendor advisory for mitigations.

References

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