CVE-2026-31610

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 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 its 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.

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/269c800a7a7e363459291885b35f7bc72e231ed6
• https://git.kernel.org/stable/c/6c8c44e6553b9f072f62d9875e567766eb293162
• https://git.kernel.org/stable/c/745a535461bbb90a56d9357573c9f97a5c12abe1
• https://git.kernel.org/stable/c/ad0057fb91218914d6c98268718ceb9d59b388e1
• https://git.kernel.org/stable/c/dd53414e301beb915fe672dc4c4a51bafb917604
• https://git.kernel.org/stable/c/dd577cb55588ec3fbc66af3621280306601c4192