Bug 2460626 (CVE-2026-31476)

Summary: CVE-2026-31476 kernel: ksmbd: do not expire session on binding failure
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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OS: Linux   
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A flaw was found in ksmbd in the Linux kernel. A remote attacker can exploit this vulnerability by sending a multichannel session binding request with an incorrect password. This improper handling of failed binding requests can cause an active session to expire, leading to a Denial of Service (DoS) for legitimate users.
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Description OSIDB Bzimport 2026-04-22 15:01:50 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ksmbd: do not expire session on binding failure

When a multichannel session binding request fails (e.g. wrong password),
the error path unconditionally sets sess->state = SMB2_SESSION_EXPIRED.
However, during binding, sess points to the target session looked up via
ksmbd_session_lookup_slowpath() -- which belongs to another connection's
user. This allows a remote attacker to invalidate any active session by
simply sending a binding request with a wrong password (DoS).

Fix this by skipping session expiration when the failed request was
a binding attempt, since the session does not belong to the current
connection. The reference taken by ksmbd_session_lookup_slowpath() is
still correctly released via ksmbd_user_session_put().
Comment 1 Keith Grant 2026-04-22 18:26:18 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042256-CVE-2026-31476-bb58@gregkh/T