ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc

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Summary

CVECVE-2026-31610
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-24 15:16:40 UTC
Updated2026-04-29 16:51:02 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc The kernel ASN.1 BER decoder calls action callbacks incrementally as it walks the input. When ksmbd_decode_negTokenInit() reaches the mechToken [2] OCTET STRING element, ksmbd_neg_token_alloc() allocates conn->mechToken immediately via kmemdup_nul(). If a later element in the same blob is malformed, then the decoder will return nonzero after the allocation is already live. This could happen if mechListMIC [3] overrunse the enclosing SEQUENCE. decode_negotiation_token() then sets conn->use_spnego = false because both the negTokenInit and negTokenTarg grammars failed. The cleanup at the bottom of smb2_sess_setup() is gated on use_spnego: if (conn->use_spnego && conn->mechToken) { kfree(conn->mechToken); conn->mechToken = NULL; } so the kfree is skipped, causing the mechToken to never be freed. This codepath is reachable pre-authentication, so untrusted clients can cause slow memory leaks on a server without even being properly authenticated. Fix this up by not checking check for use_spnego, as it's not required, so the memory will always be properly freed. At the same time, always free the memory in ksmbd_conn_free() incase some other failure path forgot to free it.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

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

EPSS: 0.000340000 probability, percentile 0.098310000 (date 2026-04-27)

Problem Types: CWE-401

CVSS v3.1 Breakdown

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

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 745a535461bbb90a56d9357573c9f97a5c12abe1 git Not specified
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 dd577cb55588ec3fbc66af3621280306601c4192 git Not specified
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 dd53414e301beb915fe672dc4c4a51bafb917604 git Not specified
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 269c800a7a7e363459291885b35f7bc72e231ed6 git Not specified
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 6c8c44e6553b9f072f62d9875e567766eb293162 git Not specified
CNA Linux Linux affected fad4161b5cd01a24202234976ebbb133f7adc0b5 ad0057fb91218914d6c98268718ceb9d59b388e1 git Not specified
CNA Linux Linux affected 5.15 Not specified
CNA Linux Linux unaffected 5.15 semver Not specified
CNA Linux Linux unaffected 6.6.136 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.83 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.24 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.14 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0.1 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/ad0057fb91218914d6c98268718ceb9d59b388e1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/745a535461bbb90a56d9357573c9f97a5c12abe1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/269c800a7a7e363459291885b35f7bc72e231ed6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/dd577cb55588ec3fbc66af3621280306601c4192 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/6c8c44e6553b9f072f62d9875e567766eb293162 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/dd53414e301beb915fe672dc4c4a51bafb917604 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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