smb: client: require a full NFS mode SID before reading mode bits

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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.

Source published

8 May 2026 13:41:53 UTC

Source modified

19 Oct 2026 19:16:27 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 7.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H