Linux Kernel up to 6.6.104/6.12.45/6.16.5/6.17-rc4 brcmf_btcoex_detach use after free

CVSS Meta Temp Score
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CTI Interest Score
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7.7$0-$5k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.6.104/6.12.45/6.16.5/6.17-rc4. It has been classified as critical. The impacted element is the function brcmf_btcoex_detach. This manipulation causes use after free. This vulnerability is tracked as CVE-2025-39863. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.6.104/6.12.45/6.16.5/6.17-rc4 and classified as critical. Affected by this vulnerability is the function brcmf_btcoex_detach. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2025-39863 since 04/16/2025. The exploitation appears to be easy. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 03/25/2026).

The vulnerability scanner Nessus provides a plugin with the ID 265463 (Linux Distros Unpatched Vulnerability : CVE-2025-39863), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.6.105, 6.12.46, 6.16.6 or 6.17-rc5 eliminates this vulnerability. Applying the patch f1150153c4e5940fe49ab51136343c5b4fe49d63/3e789f8475f6c857c88de5c5bf4b24b11a477dd7/2f6fbc8e04ca1d1d5c560be694199f847229c625/9cb83d4be0b9b697eae93d321e0da999f9cdfcfc is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (265463) and CERT Bund (WID-SEC-2025-2099). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

  • Debian Linux
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • IBM QRadar SIEM
  • SUSE openSUSE
  • RESF Rocky Linux
  • Open Source Linux Kernel
  • Dell Secure Connect Gateway

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.9
VulDB Meta Temp Score: 7.7

VulDB Base Score: 8.0
VulDB Temp Score: 7.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.8
NVD Vector: 🔒

ADP CISA Base Score: 7.8
ADP CISA Vector: 🔒

CVSSv2info

AVACAuCIA
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💳💳💳💳💳💳
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 265463
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-39863

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.6.105/6.12.46/6.16.6/6.17-rc5
Patch: f1150153c4e5940fe49ab51136343c5b4fe49d63/3e789f8475f6c857c88de5c5bf4b24b11a477dd7/2f6fbc8e04ca1d1d5c560be694199f847229c625/9cb83d4be0b9b697eae93d321e0da999f9cdfcfc

Timelineinfo

04/16/2025 CVE reserved
09/19/2025 +156 days Advisory disclosed
09/19/2025 +0 days VulDB entry created
03/25/2026 +187 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39863 (🔒)
GCVE (CVE): GCVE-0-2025-39863
GCVE (VulDB): GCVE-100-325057
CERT Bund: WID-SEC-2025-2099 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 09/19/2025 18:21
Updated: 03/25/2026 12:34
Changes: 09/19/2025 18:21 (58), 09/23/2025 03:19 (2), 10/20/2025 23:52 (7), 11/12/2025 05:12 (1), 11/29/2025 07:20 (1), 12/13/2025 06:08 (11), 12/22/2025 13:12 (1), 03/25/2026 12:34 (9)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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