Bug 2552201 (CVE-2026-98420)

Summary:	CVE-2026-98420 kernel: ksmbd: follow SMB2 session expiration semantics
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's ksmbd module. A remote client can cause a Denial of Service (DoS) by initiating a new session setup exchange on an existing Server Message Block (SMB) connection. Due to an error where session idle time is confused with credential expiration time, the server prematurely terminates valid sessions after a brief period of inactivity. This leads to the invalidation of active connections and causes mapped network drives to disconnect unexpectedly.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-14 13:43:27 UTC

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: follow SMB2 session expiration semantics

ksmbd_session_register() 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 STATUS_NETWORK_NAME_DELETED.

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 STATUS_INSUFFICIENT_RESOURCES, 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.

Comment 1 gkamathe 2026-10-15 10:19:35 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98420.mbox