CVE-2026-31610: ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Fixed in 6.6.137.1-1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-136.136 - Upgrade
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ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 7.0.0-1014.14 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-27.27.1 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-27.27.1 - Compensating control
In ksmbd_conn_free(), always free conn->mechToken when it is non-NULL; remove the use_spnego condition so mechToken is freed even when SPNEGO decoding fails.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-31610?
CVE-2026-31610 has a medium severity rating of 5.5 on the CVSS scale.
How do I fix CVE-2026-31610?
To fix CVE-2026-31610, apply the available patch provided by the kernel maintainers.
What type of vulnerability is CVE-2026-31610?
CVE-2026-31610 is a memory leak vulnerability related to the ksmbd component in the Linux kernel.
Which software versions are affected by CVE-2026-31610?
CVE-2026-31610 affects the Linux kernel and specifically the ksmbd implementation.
When was CVE-2026-31610 published?
CVE-2026-31610 was published on April 24, 2026.