How severe is CVE-2026-53390?

CVE-2026-53390 has a CVSS score of 8.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-53390?

CVE-2026-53390 affects the following packages: Kernel (Linux). Ecosystems affected: Linux.

How do I fix CVE-2026-53390?

Update Kernel to 6.1.177 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53390 is resolved across your whole dependency graph.

How do I detect CVE-2026-53390 in my Linux dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-53390 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-53390?

O3 pinpoints whether CVE-2026-53390 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-53390 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-53390 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-53390 published, and has it been updated?

CVE-2026-53390 was published on July 19, 2026 and was last updated on July 22, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐧 Linux

CVE-2026-53390

HIGH

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

Published

Jul 19, 2026

Updated

Jul 22, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Blast Radius

1 pkg affected

🐧Kernel

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Linux packages — download data is not available via public APIs for these ecosystems.

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 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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐧Linux	`Kernel`	≥ 6.2.0&&< 6.1.177	6.1.177

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Kernel. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Kernel to 6.1.177 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53390 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-53390 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-53390. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

Is CVE-2026-53390 in your dependencies?

O3 detects CVE-2026-53390 across Linux dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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