CVE-2026-31610

Technical Description

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-authenticatio

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References