CVE-2026-72221 sunrpc: wait for in-flight TLS handshake callback when cancel loses race
A race condition in the Linux kernel's sunrpc TLS handshake handling can corrupt internal state, potentially leading to a 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-2026-72221?
CVE-2026-72221 is a critical vulnerability in Linux, published on 15 Aug 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:
sunrpc: wait for in-flight TLS handshake callback when cancel loses race
When wait_for_completion_interruptible_timeout() in svc_tcp_handshake() returns 0 (timeout) or -ERESTARTSYS (signal) and tls_handshake_cancel() then returns false, handshake_complete() has won the cancellation race: it has set HANDSHAKE_F_REQ_COMPLETED and is about to invoke svc_tcp_handshake_done(), but the callback's side effects on xpt_flags and on svsk->sk_handshake_done have not yet committed.
The current code reads xpt_flags immediately to decide whether the session succeeded. Two races result.
If the callback has executed set_bit(XPT_TLS_SESSION) but not yet clear_bit(XPT_HANDSHAKE), svc_tcp_handshake() sees a session, enqueues the transport, and returns. svc_xprt_received() then clears XPT_BUSY, a worker thread picks the transport up, the dispatcher in svc_handle_xprt() observes XPT_HANDSHAKE still set, and xpo_handshake is invoked a second time. That svc_tcp_handshake() calls init_completion(&svsk->sk_handshake_done) while the original callback concurrently calls complete_all() on it, corrupting the embedded swait_queue.
If the callback has set HANDSHAKE_F_REQ_COMPLETED but not yet entered svc_tcp_handshake_done(), svc_tcp_handshake() reads XPT_TLS_SESSION as clear and tears the connection down even though the handshake is about to succeed.
Wait for the callback to commit before inspecting xpt_flags. The completion is guaranteed to fire because handshake_complete() invokes svc_tcp_handshake_done() unconditionally once it has set HANDSHAKE_F_REQ_COMPLETED.
Which versions are affected by CVE-2026-72221?
How do I fix CVE-2026-72221?
Apply the vendor's patch.
Is CVE-2026-72221 being exploited?
There is no known exploitation of CVE-2026-72221 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72221, DEBIAN-CVE-2026-72221, GHSA-5gf3-c25p-fm95, UBUNTU-CVE-2026-72221.