cbcvebase.
CVE-2026-53390
published 2026-07-19

CVE-2026-53390: 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…

PriorityP347high8.1CVSS 3.1
AVNACLPRLUINSUCHINAH
EPSS
0.47%
38.2th percentile
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 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().

Affected

21 ranges
VendorProductVersion rangeFixed in
linuxlinux——
linuxlinux——
linuxlinux>= 282cbbb476b9f35793452bc461934af4c7eca169 < c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0
linuxlinux>= 325d4ac11f526cb8964cff14548ccf02d8c756d8 < 36599894fa8536fefdf1e296c0af71b8b722685936599894fa8536fefdf1e296c0af71b8b7226859
linuxlinux>= 5.15.210 < 5.15.2125.15.212
linuxlinux>= 6.1.176 < 6.1.1776.1.177
linuxlinux>= 6.12.84 < 6.12.956.12.95
linuxlinux>= 6.18.25 < 6.18.386.18.38
linuxlinux>= 6.6.140 < 6.6.1446.6.144
linuxlinux>= 7.0.2 < 7.17.1
linuxlinux>= 90089584b2e25c4510b7b987387b4405f0673ece < 7627ff8c4f9919f14de562b0160ab4ec9d80b1f77627ff8c4f9919f14de562b0160ab4ec9d80b1f7
linuxlinux>= 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c < d5c81a095c86fe507c032d08f3a8cfc518444927d5c81a095c86fe507c032d08f3a8cfc518444927
linuxlinux>= d07b26f39246a82399661936dd0c853983cfade7 < e36e35660adb9b8ef1435ac359151dda5f094c55e36e35660adb9b8ef1435ac359151dda5f094c55
linuxlinux>= d07b26f39246a82399661936dd0c853983cfade7 < 1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b
linuxlinux>= f20adc4ef7428bc485ee83fd1a592252fb87718b < 988c93d3bba066d8669143e6ec30bb2be9608d53988c93d3bba066d8669143e6ec30bb2be9608d53
linuxlinux_kernel——
linuxlinux_kernel>= 5.15.210 < 5.15.2125.15.212
linuxlinux_kernel>= 6.12.84 < 6.12.956.12.95
linuxlinux_kernel>= 6.18.25 < 6.18.386.18.38
linuxlinux_kernel>= 6.6.140 < 6.6.1446.6.144
linuxlinux_kernel>= 7.0.2 < 7.1.37.1.3

CVSS provenance

nvdv3.18.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
vendor_redhat8.1HIGH
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