CVE-2026-98420: ksmbd: follow SMB2 session expiration semantics
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: follow SMB2 session expiration semantics
ksmbdsessionregister() destroys valid sessions after ten seconds of inactivity whenever a client starts another SessionSetup exchange. This confuses Session.IdleTime with Session.ExpirationTime. Windows can create additional authenticated sessions on an existing connection, so deleting the older session invalidates its tree connects and makes mapped drives fail with STATUSNETWORKNAMEDELETED.
The session expiration rules require the server to change a valid session to expired only after its credential expiration time passes. A valid or expired session otherwise keeps its connection from being scavenged. Connections that have not negotiated a dialect, have no sessions, or have only InProgress sessions are disconnected after an implementation-specific timeout. Use the Windows-compatible 45 second value and run the expiration check periodically for both TCP and SMB Direct.
Keep zero as an infinite credential expiration time, and count each Valid-to-Expired transition. Set expired sessions to InProgress when they reauthenticate. If authentication fails, remove the session from the global and per-connection tables immediately, including SMB3 multichannel connections.
Retain protection against abandoned SessionId-zero exchanges by allowing only one InProgress authentication per connection. Additional exchanges fail with STATUSINSUFFICIENTRESOURCES, and stale InProgress sessions are reaped after the same 45 second setup timeout. This bounds the original unauthenticated memory-exhaustion path without evicting established sessions.
Affected Software
Event History
Frequently Asked Questions
Which deployments are most likely to encounter this issue?
Linux kernel systems using ksmbd are affected in the scenario where a client, such as Windows, creates additional authenticated SMB sessions on an existing connection. Older valid sessions can then be removed even though their credential expiration time has not passed.
What symptom would indicate that a client has been affected?
Tree connects associated with the older session are invalidated, causing mapped drives to fail with STATUS_NETWORK_NAME_DELETED.
Is ordinary session inactivity alone supposed to expire an SMB2 session?
No. A valid session should become expired only after its credential expiration time passes; a credential expiration time of zero is infinite. Valid or expired sessions should also keep their connection from being scavenged.