In the Linux kernel, the following vulnerability has been resolved:

ksmbd: validate NTLMv2 response before updating session key

ksmbdauthntlmv2() derives the NTLMv2 session key into sess->sesskey before it verifies the NTLMv2 response. ksmbddecodentlmsspauthblob() then continues into KEYXCH even when ksmbdauthntlmv2() failed.

With SMB3 multichannel binding, the failed authentication operates on an existing session and the session setup error path does not expire binding sessions. A client can send a binding session setup with a bad NT proof and KEYXCH and still modify sess->sesskey before STATUSLOGONFAILURE is returned.

Relevant path:

smb2sesssetup() -> conn->binding = true -> ntlmauthenticate() -> sessionuser() -> ksmbddecodentlmsspauthblob() -> ksmbdauthntlmv2() -> calcntlmv2hash() -> hmacmd5usingrawkey(..., sess->sesskey) -> cryptomemneq() returns mismatch -> KEYXCH arc4crypt(..., sess->sesskey, ...) -> outerr without expiring the binding session

Derive the base session key into a local buffer and copy it to sess->sesskey only after the proof matches. Return immediately on authentication failure so KEYXCH is only processed after successful authentication.

This vulnerability allows remote attackers to disclose sensitive information on affected installations of Linux Kernel KSMBD. Authentication is not required to exploit this vulnerability. However, only systems with ksmbd enabled are vulnerable. The ZDI has assigned a CVSS rating of 9.3. The following CVEs are assigned: CVE-2026-68431.

In 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 ksmbddecodenegTokenInit() reaches the mechToken [2] OCTET STRING element, ksmbdnegtokenalloc() allocates conn->mechToken immediately via kmemdupnul(). 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.

decodenegotiationtoken() then sets conn->usespnego = false because both the negTokenInit and negTokenTarg grammars failed. The cleanup at the bottom of smb2sesssetup() is gated on usespnego:

if (conn->usespnego && 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 usespnego, as it's not required, so the memory will always be properly freed. At the same time, always free the memory in ksmbdconnfree() incase some other failure path forgot to free it.