CVE-2026-72123

Description

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.

Gravité et risque d'exploitation

CVE-2026-72123 obtient un score CVSS de 7.8/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.17 %, ce qui la place devant 5.8 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f, 5.10.130, <=6.1.*, 5.18.11, <=6.12.*, 6.18.40, 7.1.5, <5.10.265, 5b48f5711f1c630841ab78dcc061de902f0e37bf, 0, <5.15.216, <=7.1.*, 5.19, 5.15.216, f1b4e32aca0811aa011c76e5d6cf2fa19224b386, <4.20, 6.1.178, <=5.10.*, <=6.6.*, 6.12.97, <ce2d4b121fb7545e1ed588e860c8e5fd5ad45224, edb4baffb9483141a50fb7f7146cfe4a4c0c2db8, <5.5, 85cd41070df992d3c0dfd828866fdd243d3b774a, f34f2a18e47b73e48f90a757e1f4aaa8c7d665a1, <=6.18.*, 5.15.54, 6.6.145, <de5fce46637de05bef56ec08528127676eb6fc9b, <5.19, <036a8c320ca11bc912e8027adcfad14b326f067e, 5.4.205, <cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5, <=*, fbac09a3b8890003c0c55294c00709f3ae5501bb, <=5.15.*, <68973f9db76144825e4f35dfdc80fb8279eb2d57, <4177762f70646ac48a2af382e45a795cbd295198, <3cf4fd5316f449811d8baf1bc6978ef5a7b743a9, 5.10.265, 7.2, 4.19.252) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/de5fce46637de05bef56ec08528127676eb6fc9b
• https://git.kernel.org/stable/c/036a8c320ca11bc912e8027adcfad14b326f067e
• https://git.kernel.org/stable/c/3cf4fd5316f449811d8baf1bc6978ef5a7b743a9
• https://git.kernel.org/stable/c/4177762f70646ac48a2af382e45a795cbd295198
• https://git.kernel.org/stable/c/6fd08e8d826c3aa4cc7021f5f9cdbb7fa7441d3f
• https://git.kernel.org/stable/c/cd830e0bc25ee2d38cbfbdbb3cd77c5f53b2b6d5
• https://git.kernel.org/stable/c/ce2d4b121fb7545e1ed588e860c8e5fd5ad45224
• https://git.kernel.org/stable/c/68973f9db76144825e4f35dfdc80fb8279eb2d57