CVE-2026-72124 can: isotp: serialize TX state transitions under so->rx_lock
A race condition in the Linux kernel CAN ISO-TP driver allows concurrent access to TX state, potentially corrupting transfers and causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72124?
CVE-2026-72124 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
can: isotp: serialize TX state transitions under so->rx_lock
The TX state machine (so->tx.state) is driven from three contexts: sendmsg() claiming and progressing a transfer, the RX path consuming Flow Control/echo frames, and two hrtimers timing out a stalled transfer. Mixing a lock-free cmpxchg() claim in sendmsg() with hrtimer_cancel() calls made under so->rx_lock elsewhere left windows where a frame or timer callback could act on a state that had already moved on, corrupting an unrelated transfer.
so->rx_lock now covers the full lifecycle of a TX claim: sendmsg() takes it to check so->tx.state is ISOTP_IDLE, switch it to ISOTP_SENDING, bump so->tx_gen and drain the previous transfer's timers - all as one critical section. isotp_rcv_fc()/isotp_rcv_cf() already run under this lock via isotp_rcv(), and isotp_rcv_echo() now takes it itself, so none of them can ever observe a transfer mid-claim. This also means a transfer can no longer be handed to sendmsg()'s cleanup paths (signal or send error) while another thread is concurrently claiming or finishing it, so those paths can cancel timers and reset the state unconditionally.
isotp_release() claims the socket the same way, so a racing sendmsg() sees a consistent ISOTP_SHUTDOWN and skips arming its timer or sending.
Only the hrtimer callbacks stay outside so->rx_lock, since they run under so->rx_lock's cancellation elsewhere and taking it themselves would deadlock. so->tx_gen lets them recognize whether the transfer they timed out is still the one currently active, so they don't report an error against a transfer that has since completed or been superseded.
Which versions are affected by CVE-2026-72124?
How do I fix CVE-2026-72124?
Apply the vendor's patch.
Is CVE-2026-72124 being exploited?
There is no known exploitation of CVE-2026-72124 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72124, DEBIAN-CVE-2026-72124, GHSA-h95p-28wv-6wpp, UBUNTU-CVE-2026-72124.