CVE-2026-90153 ksmbd: bound smb_check_perm_dacl() ACE walks by DACL size
A flaw in the Linux kernel ksmbd server allows attackers to bypass access controls by crafting DACLs, potentially leading to unauthorized data access or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90153?
CVE-2026-90153 is a high-severity missing authorization vulnerability in Linux, published on 17 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: bound smb_check_perm_dacl() ACE walks by DACL size
smb_check_perm_dacl() validates that the DACL fits inside the NT security descriptor, but then bounds its two ACE walks by the remaining NTSD length (acl_size) rather than the DACL's declared size (pdacl_size).
When pdacl->size is smaller than the trailing NTSD buffer, bytes after the declared DACL boundary - still inside the stored security descriptor - are parsed as ACEs during access checks. A crafted DACL can place an access-granting ACE beyond pdacl->size, and the current code accepts it during SMB2_CREATE access validation, while parse_dacl() and smb_inherit_dacl() stop at pdacl_size.
Bound both ACE walks by pdacl_size to match the DACL boundary semantics used elsewhere in the server.
Validation: - semantic KUnit harness shows the post-boundary ACE is selected before the fix and rejected (EACCES) after it - linux master (7.2-rc6), x86_64
Which versions are affected by CVE-2026-90153?
How do I fix CVE-2026-90153?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-90153 being exploited?
There is no known exploitation of CVE-2026-90153 in the wild and no public exploit code.
Sources
Also known as AZL-102458, BELL-CVE-2026-90153, DEBIAN-CVE-2026-90153, GHSA-wffx-7972-vw67, UBUNTU-CVE-2026-90153.