CVE-2026-72123: Linux

High severity, CVSS 7.8. EPSS: 0.2% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: can: bcm: defer rx_op deallocation to workqueue to fix thrtimer UAF Commit f1b4e32aca08 ("can: bcm: use call_rcu() instead of costly synchronize_rcu()") replaced synchronize_rcu() in bcm_delete_rx_op() with call_rcu() and introduced the RX_NO_AUTOTIMER flag. However, this flag check was omitted for thrtimer in the packet rx fast-path. During BCM RX operation teardown, a concurrent RCU reader (bcm_rx_handler) can race and re-arm thrtimer via bcm_rx_update_and_send() after call_rcu() has been scheduled. Once the RCU grace period elapses, bcm_op is freed. The subsequently firing thrtimer then dereferences the deallocated op, causing a UAF. Adding flag checks to the rx fast-path (bcm_rx_update_and_send) does not fully close the TOCTOU race and introduces latency for every CAN frame. Conversely, calling hrtimer_cancel() directly inside the RCU callback (softirq context) is fatal as hrtimer_cancel() can sleep, triggering a "scheduling while atomic" panic. Resolve this by deferring the timer cancellation and memory free to a dedicated unbound workqueue (bcm_wq). The RCU callback now queues a work item to bcm_wq, which safely cancels both timers and deallocates memory in sleepable process context. A dedicated workqueue is used to prevent system-wide WQ saturation and is cleanly flushed/destroyed on module unload to avoid rmmod page faults. Since the deferred work can now outlive the calling context by an unbounded amount, also take a reference on op->sk when it is assigned and drop it only once the deferred work has cancelled both timers, so a socket can no longer be freed out from under a still-armed timer whose callback (bcm_send_to_user()) dereferences op->sk.

Affected products

• Linux Linux: from 5.10.130, before 5.10.265 (fixed in 5.10.265); from 5.15.54, before 5.15.216 (fixed in 5.15.216); from 4.19.252, before 4.20 (fixed in 4.20); from 5.4.205, before 5.5 (fixed in 5.5); from 5.18.11, before 5.19 (fixed in 5.19); from 5.19, before 6.1.178 (fixed in 6.1.178); …

Published 2026-08-15. Last modified 2026-08-19.