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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-53390
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 12:16:50 UTC
Updated2026-07-20 15:16:41 UTC
DescriptionIn 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().

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.001720000 probability, percentile 0.069020000 (date 2026-07-20)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
3.1CNADECLARED8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected f20adc4ef7428bc485ee83fd1a592252fb87718b 988c93d3bba066d8669143e6ec30bb2be9608d53 git Not specified
CNA Linux Linux affected 325d4ac11f526cb8964cff14548ccf02d8c756d8 36599894fa8536fefdf1e296c0af71b8b7226859 git Not specified
CNA Linux Linux affected 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c d5c81a095c86fe507c032d08f3a8cfc518444927 git Not specified
CNA Linux Linux affected 90089584b2e25c4510b7b987387b4405f0673ece 7627ff8c4f9919f14de562b0160ab4ec9d80b1f7 git Not specified
CNA Linux Linux affected d07b26f39246a82399661936dd0c853983cfade7 e36e35660adb9b8ef1435ac359151dda5f094c55 git Not specified
CNA Linux Linux affected d07b26f39246a82399661936dd0c853983cfade7 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b git Not specified
CNA Linux Linux affected 282cbbb476b9f35793452bc461934af4c7eca169 git Not specified
CNA Linux Linux affected 151b1799861fde38087c08f613abc2843ef597b0 git Not specified
CNA Linux Linux affected 6.1.176 6.1.177 semver Not specified
CNA Linux Linux affected 6.6.140 6.6.144 semver Not specified
CNA Linux Linux affected 6.12.84 6.12.95 semver Not specified
CNA Linux Linux affected 6.18.25 6.18.38 semver Not specified
CNA Linux Linux affected 5.15.210 5.16 semver Not specified
CNA Linux Linux affected 7.0.2 7.1 semver Not specified
CNA Linux Linux affected 7.1 Not specified
CNA Linux Linux unaffected 7.1 semver Not specified
CNA Linux Linux unaffected 6.1.177 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.144 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.95 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.38 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.3 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d5c81a095c86fe507c032d08f3a8cfc518444927 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e36e35660adb9b8ef1435ac359151dda5f094c55 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/988c93d3bba066d8669143e6ec30bb2be9608d53 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/36599894fa8536fefdf1e296c0af71b8b7226859 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7627ff8c4f9919f14de562b0160ab4ec9d80b1f7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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