CVE-2026-74494: ksmbd: reject repeated SMB2 NEGOTIATE requests
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: reject repeated SMB2 NEGOTIATE requests
Unauthenticated client can send multiple successful SMB2 NEGOTIATE requests on one connection before SESSIONSETUP. While the connection is in KSMBDSESSNEEDSETUP, smb2handlenegotiate() accepts another SMB3.1.1 NEGOTIATE and overwrites conn->preauthinfo with a new allocation. Only the final allocation is freed when the connection is released, leaking one object for every additional successful request.
A repeated SMB2 NEGOTIATE after a dialect has been selected is a protocol violation. MS-SMB2 section 3.3.5.4 requires the server to disconnect without replying in this case. Set the connection exiting when rejecting the request, in addition to suppressing the response.
Reject SMB2 NEGOTIATE unless the connection is new or is waiting for the SMB2 NEGOTIATE that follows an SMB1 multi-protocol negotiate. Serialize both SMB1 and SMB2 negotiation paths under conn->srvmutex, since they update connection-wide dialect and negotiation state.
Move the locking contract to ksmbdsmbnegotiatecommon(), where the state and dialect are selected, and add ksmbdconnnew() for consistent state access.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
Reject SMB2 NEGOTIATE requests when they are repeated for an existing connection state (after a dialect has already been selected), suppressing the response and setting the connection to exit in this case.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-74494?
CVE-2026-74494 has a risk rating of 22, indicating a critical severity level.
How do I fix CVE-2026-74494?
To mitigate CVE-2026-74494, ensure you update your Linux kernel to the latest version where this vulnerability has been resolved.
What is the impact of CVE-2026-74494?
CVE-2026-74494 allows unauthenticated clients to send repeated SMB2 NEGOTIATE requests, potentially leading to denial of service.
Which versions of the Linux kernel are affected by CVE-2026-74494?
CVE-2026-74494 affects specific versions of the Linux kernel prior to the security update addressing this vulnerability.
Is CVE-2026-74494 exploitable remotely?
Yes, CVE-2026-74494 can be exploited by unauthenticated remote clients sending multiple SMB2 NEGOTIATE requests.