ZephyrProject Zephyr prior 4.4.2 Audio Gateway hfp_ag.c hfp_ag_disconnected acl_conn/ongoing_call_work/slc_work null pointer dereference

Summaryinfo

A vulnerability described as critical has been identified in ZephyrProject Zephyr prior 4.4.2. Affected by this issue is the function hfp_ag_disconnected of the file subsys/bluetooth/host/classic/hfp_ag.c of the component Audio Gateway. Executing a manipulation of the argument acl_conn/ongoing_call_work/slc_work can lead to null pointer dereference. The identification of this vulnerability is CVE-2026-19940. The attack may be launched remotely. There is no exploit available. It is best practice to apply a patch to resolve this issue.

Detailsinfo

A vulnerability was found in ZephyrProject Zephyr prior 4.4.2. It has been declared as critical. This vulnerability affects the function hfp_ag_disconnected of the file subsys/bluetooth/host/classic/hfp_ag.c of the component Audio Gateway. The manipulation of the argument acl_conn/ongoing_call_work/slc_work with an unknown input leads to a null pointer dereference vulnerability. The CWE definition for the vulnerability is CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. As an impact it is known to affect availability. CVE summarizes:

The Bluetooth Classic Hands-Free Profile Audio Gateway implementation in subsys/bluetooth/host/classic/hfp_ag.c keeps its struct bt_hfp_ag objects in a static pool indexed by ACL connection index. On link teardown, hfp_ag_disconnected() cancels ag->tx_work and the per-call work items and then clears ag->acl_conn, which marks the pool slot as free — but it leaves ag->ongoing_call_work (and ag->slc_work) untouched. The next connection that lands on the same slot enters hfp_ag_create(), whose only occupancy test is ag->acl_conn, and immediately executes memset(ag, 0, sizeof(struct bt_hfp_ag)) followed by k_work_init_delayable(). Zeroing and re-initialising a k_work_delayable whose struct _timeout node is still linked into the kernel timeout list leaves the kernel holding a reference to a node with NULL prev/next links. ag->ongoing_call_work is armed by the remote peer: when a Hands-Free unit sends AT+CIND? during Service Level Connection establishment and the application provides the asynchronous get_ongoing_call callback, the AG schedules the work for CONFIG_BT_HFP_AG_GET_ONGOING_CALL_TIMEOUT milliseconds (default 10000). The timer is cancelled only if the application answers in time via bt_hfp_ag_ongoing_calls(). A peer that sends AT+CIND?, then disconnects the HFP RFCOMM DLC, then immediately re-opens it on the same ACL link, reuses the same pool slot deterministically while the timeout is still pending — the AG's RFCOMM server accept path (hfp_ag_accept()) calls hfp_ag_create() directly, so the remote side drives both teardown and re-creation. The result is corruption of the kernel's timeout list: sys_dlist_remove() on the zeroed node performs writes through NULL pointers from the clock-announce path, and rescheduling the re-initialised work re-inserts a node the list already references, creating a cycle that the announce loop walks with interrupts locked. The observable impact is a fault or hang of the whole system, i.e. a denial of service reachable from Bluetooth radio range; no attacker-controlled data is written, so this does not by itself yield code execution. Exposure is limited to builds with CONFIG_BT_HFP_AG (marked experimental and disabled by default) whose application implements the asynchronous get_ongoing_call callback.

The advisory is available at github.com. This vulnerability was named CVE-2026-19940 since 08/15/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit.

Applying the patch 204c36b896fe8d68ca3cb3d00216f245f91d14be is able to eliminate this problem.

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Productinfo

Type

• Project Management Software

Vendor

• ZephyrProject

Name

• Zephyr

Version

• <4.4.2

CPE 2.3info

• 🔒

CPE 2.2info

• 🔒

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