CVE-2025-68775 net/handshake: duplicate handshake cancellations leak socket
Duplicate handshake cancellations in the Linux kernel cause a socket reference count underflow, leading to resource leaks and potential denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-68775?
CVE-2025-68775 is a critical denial of service vulnerability in Linux, published on 13 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net/handshake: duplicate handshake cancellations leak socket
When a handshake request is cancelled it is removed from the handshake_net->hn_requests list, but it is still present in the handshake_rhashtbl until it is destroyed.
If a second cancellation request arrives for the same handshake request, then remove_pending() will return false... and assuming HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue processing through the out_true label, where we put another reference on the sock and a refcount underflow occurs.
This can happen for example if a handshake times out - particularly if the SUNRPC client sends the AUTH_TLS probe to the server but doesn't follow it up with the ClientHello due to a problem with tlshd. When the timeout is hit on the server, the server will send a FIN, which triggers a cancellation request via xs_reset_transport(). When the timeout is hit on the client, another cancellation request happens via xs_tls_handshake_sync().
Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel path so duplicate cancels can be detected.
Weakness: CWE-662
Which versions are affected by CVE-2025-68775?
How do I fix CVE-2025-68775?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-68775 being exploited?
There is no known exploitation of CVE-2025-68775 in the wild and no public exploit code.
Sources
Also known as AZL-74456, BELL-CVE-2025-68775, DEBIAN-CVE-2025-68775, GHSA-jpgq-r68h-x9q2, ROOT-OS-UBUNTU-2404-CVE-2025-68775, UBUNTU-CVE-2025-68775.