In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix out-of-bounds read in smbcheckperm_dacl()
The permission-check ACE walk in smbcheckpermdacl() validates the ACE header size and caps sid.numsubauth at SIDMAXSUBAUTHORITIES, but it never checks that ace->size is actually large enough to contain numsubauth sub-authorities before compare_sids() dereferences them.
CIFSSIDBASESIZE covers the SID header up to but excluding the subauth[] array, and offsetof(struct smbace, sid) is the ACE header, so the existing guards only guarantee the 8-byte SID base, i.e. zero sub-authorities. comparesids() then reads ace->sid.subauth[i] for i < min(localsid->numsubauth, ace->sid.numsubauth). The local comparison SIDs (sideveryone, sidunixNFSmode, and the idtosid() 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 numsubauth >= 1 placed at the tail of the security descriptor therefore causes a heap out-of-bounds read of up to SIDMAXSUBAUTHORITIES * sizeof(_le32) bytes past the pntsd allocation. The security descriptor is loaded by ksmbdvfsgetsdxattr() into a buffer sized exactly to the on-disk data (kzalloc(sdsize) in ndrdecodev4ntacl()), so the read lands past the allocation. The malformed descriptor can be stored verbatim via SMB2SETINFO (the DACL is not normalised before being written to the security.NTACL xattr) and the read fires on a subsequent SMB2CREATE access check, making this reachable by an authenticated client on a share that uses ACL xattrs.
Add the missing numsubauth-versus-acesize check, mirroring the identical guards already present in the sibling parsers parsedacl() and smbinherit_dacl().
{
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53390.json",
"cna_assigner": "Linux"
}