CVE-2026-53390ksmbd: fix out-of-bounds read in smb_check_perm_dacl()

Description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix out-of-bounds read in smb_check_perm_dacl() The permission-check ACE walk in smb_check_perm_dacl() validates the ACE header size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it never checks that ace->size is actually large enough to contain num_subauth sub-authorities before compare_sids() dereferences them. CIFS_SID_BASE_SIZE covers the SID header up to but excluding the sub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header, so the existing guards only guarantee the 8-byte SID base, i.e. zero sub-authorities. compare_sids() then reads ace->sid.sub_auth[i] for i < min(local_sid->num_subauth, ace->sid.num_subauth). The local comparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid() result) always have at least one sub-authority, and an attacker controls the ACE revision and authority bytes (which lie within the in-bounds SID base), so they can match one of those SIDs and force the sub_auth read. A crafted ACE with size == 16 and num_subauth >= 1 placed at the tail of the security descriptor therefore causes a heap out-of-bounds read of up to SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd allocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr() into a buffer sized exactly to the on-disk data (kzalloc(sd_size) in ndr_decode_v4_ntacl()), so the read lands past the allocation. The malformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL is not normalised before being written to the security.NTACL xattr) and the read fires on a subsequent SMB2_CREATE access check, making this reachable by an authenticated client on a share that uses ACL xattrs. Add the missing num_subauth-versus-ace_size check, mirroring the identical guards already present in the sibling parsers parse_dacl() and smb_inherit_dacl().

Timeline

Scores

EPSS (exploitation in 30 days)

0.47% · top 59% of all CVEs (14 Nov 2026)

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.1.

Affected products

• Linux · Linux

  • affected 282cbbb476b9f35793452bc461934af4c7eca169 – < c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0
  • affected f20adc4ef7428bc485ee83fd1a592252fb87718b – < 988c93d3bba066d8669143e6ec30bb2be9608d53
  • affected 325d4ac11f526cb8964cff14548ccf02d8c756d8 – < 36599894fa8536fefdf1e296c0af71b8b7226859
  • affected 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c – < d5c81a095c86fe507c032d08f3a8cfc518444927
  • affected 90089584b2e25c4510b7b987387b4405f0673ece – < 7627ff8c4f9919f14de562b0160ab4ec9d80b1f7
  • affected d07b26f39246a82399661936dd0c853983cfade7 – < e36e35660adb9b8ef1435ac359151dda5f094c55
  • affected d07b26f39246a82399661936dd0c853983cfade7 – < 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b
  • affected 151b1799861fde38087c08f613abc2843ef597b0
  • affected 5.15.210 – < 5.15.212
  • affected 6.1.176 – < 6.1.177
  • affected 6.6.140 – < 6.6.144
  • affected 6.12.84 – < 6.12.95
  • affected 6.18.25 – < 6.18.38
  • affected 7.0.2 – < 7.1

• Linux · Linux

  • affected 7.1
  • unaffected < 7.1
  • unaffected 5.15.212 – ≤ 5.15.*
  • unaffected 6.1.177 – ≤ 6.1.*
  • unaffected 6.6.144 – ≤ 6.6.*
  • unaffected 6.12.95 – ≤ 6.12.*
  • unaffected 6.18.38 – ≤ 6.18.*
  • unaffected 7.1.3 – ≤ 7.1.*
  • unaffected 7.2 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-45512 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-53390](https://cveledger.app/badge/CVE-2026-53390.svg)](https://cveledger.app/cve/CVE-2026-53390)

Record last updated 17 Aug 2026, 04:50 UTC.