CVE-2026-93282 ksmbd: fix maximum allowed access checks
Flawed access control checks in ksmbd allow unauthorized file access or privilege escalation by mishandling Authenticated Users ACEs and maximal access calculations.
- 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-2026-93282?
CVE-2026-93282 is a high-severity missing authorization vulnerability in Linux, published on 24 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: fix maximum allowed access checks
The DACL permission check looks for an ACE matching the current user and falls back to the Everyone ACE. It does not consider an Authenticated Users ACE, even though an authenticated session is a member of that well-known group.
As a result, opening a file whose access is granted through S-1-5-11 can incorrectly fail with STATUS_ACCESS_DENIED. Treat an Authenticated Users ACE as a fallback entry alongside Everyone.
The maximal access calculation also combines access masks from every ACE, regardless of whether its SID applies to the current user. This can grant rights belonging to an unrelated principal. Process only ACEs applying to the user, Everyone, or Authenticated Users, and accumulate allowed and denied masks in ACL order. Preserve explicitly requested access bits so they are validated against the resulting maximal mask.
When ACCESS_SYSTEM_SECURITY is denied, report STATUS_PRIVILEGE_NOT_HELD instead of the generic STATUS_ACCESS_DENIED. Access to the system ACL requires a security privilege that ksmbd does not grant.
For regular files, include FILE_EXECUTE in maximal access when the client requested GENERIC_EXECUTE and the DACL grants the complete file-read set. Keep a direct FILE_EXECUTE request subject to the explicit DACL bit. This matches the POSIX file ACL mapping without broadening specific execute requests.
Do not replace rights from an applicable NT ACE with a POSIX ACL entry. The POSIX ACL is only a fallback when no user, Everyone, or Authenticated Users ACE applies; otherwise it can incorrectly broaden the stored DACL.
This fixes smb2.maximum_allowed.maximum_allowed.
Which versions are affected by CVE-2026-93282?
How do I fix CVE-2026-93282?
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-2026-93282 being exploited?
There is no known exploitation of CVE-2026-93282 in the wild and no public exploit code.
Sources
Also known as AZL-103583, BELL-CVE-2026-93282, DEBIAN-CVE-2026-93282, GHSA-7xq8-4f3j-v3g7, UBUNTU-CVE-2026-93282.