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CVE-2025-39863

Estado: ModificadaAlta (7.8)—

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.

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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:

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:

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.

Detalles técnicos trazas, registros y código del informe original
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

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|
   */                           |

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

CVE-2025-39863 es una vulnerabilidad local (AV:L/PR:L) de use-after-free (CWE-416) en el kernel Linux. El vector sin interacción del usuario (UI:N) y acceso local con privilegios indican escalada (T1068). La ejecución de código arbitrario mediante el desbordamiento de memoria en el worker thread per

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Execution PreventionThreat Intelligence ProgramRestrict Web-Based ContentPrivileged Account ManagementLimit Software InstallationBehavior Prevention on Endpoint

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nwifi: brcmfmac: fix use-after-free when rescheduling brcmf_btcoex_info work\n\nThe brcmf_btcoex_detach() only shuts down the btcoex timer, if the\nflag timer_on is false. However, the brcmf_btcoex_timerfunc(), which\nruns as timer handler, sets timer_on to false. This creates critical\nrace conditions:\n\n1.If brcmf_btcoex_detach() is called while brcmf_btcoex_timerfunc()\nis executing, it may observe timer_on as false and skip the call to\ntimer_shutdown_sync().\n\n2.The brcmf_btcoex_timerfunc() may then reschedule the brcmf_btcoex_info\nworker after the cancel_work_sync() has been executed, resulting in\nuse-after-free bugs.\n\nThe use-after-free bugs occur in two distinct scenarios, depending on\nthe timing of when the brcmf_btcoex_info struct is freed relative to\nthe execution of its worker thread.\n\nScenario 1: Freed before the worker is scheduled\n\nThe brcmf_btcoex_info is deallocated before the worker is scheduled.\nA race condition can occur when schedule_work(&bt_local->work) is\ncalled after the target memory has been freed. The sequence of events\nis detailed below:\n\nCPU0                           | CPU1\nbrcmf_btcoex_detach            | brcmf_btcoex_timerfunc\n                               |   bt_local->timer_on = false;\n  if (cfg->btcoex->timer_on)   |\n    ...                        |\n  cancel_work_sync();          |\n  ...                          |\n  kfree(cfg->btcoex); // FREE  |\n                               |   schedule_work(&bt_local->work); // USE\n\nScenario 2: Freed after the worker is scheduled\n\nThe brcmf_btcoex_info is freed after the worker has been scheduled\nbut before or during its execution. In this case, statements within\nthe brcmf_btcoex_handler() — such as the container_of macro and\nsubsequent dereferences of the brcmf_btcoex_info object will cause\na use-after-free access. The following timeline illustrates this\nscenario:\n\nCPU0                            | CPU1\nbrcmf_btcoex_detach             | brcmf_btcoex_timerfunc\n                                |   bt_local->timer_on = false;\n  if (cfg->btcoex->timer_on)    |\n    ...                         |\n  cancel_work_sync();           |\n  ...                           |   schedule_work(); // Reschedule\n                                |\n  kfree(cfg->btcoex); // FREE   |   brcmf_btcoex_handler() // Worker\n  /*                            |     btci = container_of(....); // USE\n   The kfree() above could      |     ...\n   also occur at any point      |     btci-> // USE\n   during the worker's execution|\n   */                           |\n\nTo resolve the race conditions, drop the conditional check and call\ntimer_shutdown_sync() directly. It can deactivate the timer reliably,\nregardless of its current state. Once stopped, the timer_on state is\nthen set to false."
    }
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