Linux kernel ksmbd OOB read in smb_check_perm_dacl()
CVE-2026-53390 Published on July 19, 2026
ksmbd: fix out-of-bounds read in smb_check_perm_dacl()
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().
Products Associated with CVE-2026-53390
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Affected Versions
Linux:- Version 282cbbb476b9f35793452bc461934af4c7eca169 and below c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0 is affected.
- Version f20adc4ef7428bc485ee83fd1a592252fb87718b and below 988c93d3bba066d8669143e6ec30bb2be9608d53 is affected.
- Version 325d4ac11f526cb8964cff14548ccf02d8c756d8 and below 36599894fa8536fefdf1e296c0af71b8b7226859 is affected.
- Version 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c and below d5c81a095c86fe507c032d08f3a8cfc518444927 is affected.
- Version 90089584b2e25c4510b7b987387b4405f0673ece and below 7627ff8c4f9919f14de562b0160ab4ec9d80b1f7 is affected.
- Version d07b26f39246a82399661936dd0c853983cfade7 and below e36e35660adb9b8ef1435ac359151dda5f094c55 is affected.
- Version d07b26f39246a82399661936dd0c853983cfade7 and below 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b is affected.
- Version 151b1799861fde38087c08f613abc2843ef597b0 is affected.
- Version 5.15.210 and below 5.15.212 is affected.
- Version 6.1.176 and below 6.1.177 is affected.
- Version 6.6.140 and below 6.6.144 is affected.
- Version 6.12.84 and below 6.12.95 is affected.
- Version 6.18.25 and below 6.18.38 is affected.
- Version 7.0.2 and below 7.1 is affected.
- Version 7.1 is affected.
- Before 7.1 is unaffected.
- Version 5.15.212, <= 5.15.* is unaffected.
- Version 6.1.177, <= 6.1.* is unaffected.
- Version 6.6.144, <= 6.6.* is unaffected.
- Version 6.12.95, <= 6.12.* is unaffected.
- Version 6.18.38, <= 6.18.* is unaffected.
- Version 7.1.3, <= 7.1.* is unaffected.
- Version 7.2, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.