smb: client: fail DACL rewrite when the new DACL exceeds 64K

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-97559
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:06 UTC
Updated2026-09-25 11:17:06 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: smb: client: fail DACL rewrite when the new DACL exceeds 64K replace_sids_and_copy_aces() and set_chmod_dacl() accumulate the size of the DACL they build in a u16. That accumulator can wrap. validate_dacl() caps num_aces at (dacl_size - sizeof(struct smb_acl)) / 20, i.e. 3276 for a maximally sized DACL, while each rewritten ACE can grow to sizeof(struct smb_ace) (76 bytes) once its SID is replaced with one carrying SID_MAX_SUB_AUTHORITIES sub-authorities. The worst case is therefore sizeof(struct smb_acl) + 3276 * 76 = 248984 bytes, far beyond what a u16 can hold. A wraparound is reached with 863 ACEs. After the wraparound, ndacl_ptr->size becomes meaningless and the offset will point anywhere in the ACE array. As a result, we will see corruption of the DACL, which then gets sent to the server. This is not an out-of-bounds write as the allocation now covers the worst-case expansion, so writes will always go into the buffer. Adjust the code to use a u32 internally and return -EOVERFLOW in the overflow case. The operation must be refused, because a DACL can only hold 2^16-1 bytes on the wire and larger DACLs cannot be represented. set_chmod_dacl() carries the same pattern and is fixed the same way. It only wraps once the source DACL comes within roughly 380 bytes of the 64K ceiling, but the failure mode is identical.

Risk And Classification

EPSS: 0.001980000 probability, percentile 0.085910000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected f5065508897a922327f32223082325d10b069ebc 2ef532a01f44687f5b95001e88247cf05bff9892 git Not specified
CNA Linux Linux affected f5065508897a922327f32223082325d10b069ebc ee13d687d06a6fbb2008625dd560c654231b28e0 git Not specified
CNA Linux Linux affected f5065508897a922327f32223082325d10b069ebc d05045177a855386bca5e1909e08d06290e6e3b3 git Not specified
CNA Linux Linux affected 5.12 Not specified
CNA Linux Linux unaffected 5.12 semver Not specified
CNA Linux Linux unaffected 6.18.53 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/2ef532a01f44687f5b95001e88247cf05bff9892 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ee13d687d06a6fbb2008625dd560c654231b28e0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d05045177a855386bca5e1909e08d06290e6e3b3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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