ksmbd: fix maximum allowed access checks

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Summary

CVECVE-2026-93282
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-24 16:17:25 UTC
Updated2026-09-25 13:17:18 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 8.1 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

EPSS: 0.003080000 probability, percentile 0.211400000 (date 2026-09-27)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED8.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 35d5c59fe6b1d9fe43fb14eb384f69ee1a120f9c git Not specified
CNA Linux Linux affected e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 cc2f133e80eb2c4a04bfa77a2f207749fe2f516a git Not specified
CNA Linux Linux affected 5.15 Not specified
CNA Linux Linux unaffected 5.15 semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/35d5c59fe6b1d9fe43fb14eb384f69ee1a120f9c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cc2f133e80eb2c4a04bfa77a2f207749fe2f516a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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