CVE-2026-53390

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References