CVE-2025-39863

Description

In the Linux kernel, the following vulnerability has been resolved: wifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work The brcmf_btcoex_detach() only shuts down the btcoex timer, if the flag timer_on is false. However, the brcmf_btcoex_timerfunc(), which runs as timer handler, sets timer_on to false. This creates critical race conditions: 1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc() is executing, it may observe timer_on as false and skip the call to timer_shutdown_sync(). 2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info worker after the cancel_work_sync() has been executed, resulting in use-after-free bugs. The use-after-free bugs occur in two distinct scenarios, depending on the timing of when the brcmf_btcoex_info struct is freed relative to the execution of its worker thread. Scenario 1: Freed before the worker is scheduled The brcmf_btcoex_info is deallocated before the worker is scheduled. A race condition can occur when schedule_work(&bt_local->work) is called after the target memory has been freed. The sequence of events is detailed below: CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | kfree(cfg->btcoex); // FREE | | schedule_work(&bt_local->work); // USE Scenario 2: Freed after the worker is scheduled The brcmf_btcoex_info is freed after the worker has been scheduled but before or during its execution. In this case, statements within the brcmf_btcoex_handler() — such as the container_of macro and subsequent dereferences of the brcmf_btcoex_info object will cause a use-after-free access. The following timeline illustrates this scenario: CPU0 | CPU1 brcmf_btcoex_detach | brcmf_btcoex_timerfunc | bt_local->timer_on = false; if (cfg->btcoex->timer_on) | ... | cancel_work_sync(); | ... | schedule_work(); // Reschedule | kfree(cfg->btcoex); // FREE | brcmf_btcoex_handler() // Worker /* | btci = container_of(....); // USE The kfree() above could | ... also occur at any point | btci-> // USE during the worker's execution| */ | To resolve the race conditions, drop the conditional check and call timer_shutdown_sync() directly. It can deactivate the timer reliably, regardless of its current state. Once stopped, the timer_on state is then set to false.

Gravité et risque d'exploitation

CVE-2025-39863 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 0.16 %, ce qui la place devant 5.0 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <=6.12.*, <=6.16.*, <c75600e69e66a751cc046cd9c407b942f298d852, 6.17, 0, 6.12.46, <9cb83d4be0b9b697eae93d321e0da999f9cdfcfc, 5.15.210, <ae58f70bde0433f27ef4b388ab50634736607bf6, <f1150153c4e5940fe49ab51136343c5b4fe49d63, <3.10, <2f6fbc8e04ca1d1d5c560be694199f847229c625, <=6.6.*, 6.16.6, 6.6.105, 6.1.167, <3e789f8475f6c857c88de5c5bf4b24b11a477dd7, 61730d4dfffc2cc9d3a49fad87633008105c18ba, <=*, <=5.15.*, 3.10) 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/c75600e69e66a751cc046cd9c407b942f298d852
• https://git.kernel.org/stable/c/ae58f70bde0433f27ef4b388ab50634736607bf6
• https://git.kernel.org/stable/c/f1150153c4e5940fe49ab51136343c5b4fe49d63
• https://git.kernel.org/stable/c/3e789f8475f6c857c88de5c5bf4b24b11a477dd7
• https://git.kernel.org/stable/c/2f6fbc8e04ca1d1d5c560be694199f847229c625
• https://git.kernel.org/stable/c/9cb83d4be0b9b697eae93d321e0da999f9cdfcfc