FKIE_CVE-2026-31611

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/08f9e6d899b5c834bbcc239eae1bed58d9b15d2c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/46bbcd3ebfb3549c8da1838fc4493e79bd3241e7
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d2454f4a002d08560a60f214f392e6491cf11560
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: require 3 sub-authorities before reading sub_auth[2]\n\nparse_dacl() compares each ACE SID against sid_unix_NFS_mode and on\nmatch reads sid.sub_auth[2] as the file mode.  If sid_unix_NFS_mode is\nthe prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares\nonly min(num_subauth, 2) sub-authorities so a client SID with\nnum_subauth = 2 and sub_auth = {88, 3} will match.\n\nIf num_subauth = 2 and the ACE is placed at the very end of the security\ndescriptor, sub_auth[2] will be  4 bytes past end_of_acl.  The\nout-of-band bytes will then be masked to the low 9 bits and applied as\nthe file\u0027s POSIX mode, probably not something that is good to have\nhappen.\n\nFix this up by forcing the SID to actually carry a third sub-authority\nbefore reading it at all."
    }
  ],
  "id": "CVE-2026-31611",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:40.360",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/08f9e6d899b5c834bbcc239eae1bed58d9b15d2c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/46bbcd3ebfb3549c8da1838fc4493e79bd3241e7"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d2454f4a002d08560a60f214f392e6491cf11560"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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