Zephyr Project up to 4.4.2 AVDTP Signalling Layer avdtp.c bt_avdtp_l2cap_disconnected use after free

Summaryinfo

A vulnerability classified as problematic was found in Zephyr Project Zephyr up to 4.4.2. This vulnerability affects the function bt_avdtp_l2cap_disconnected of the file subsys/bluetooth/host/classic/avdtp.c of the component AVDTP Signalling Layer. The manipulation results in use after free. This vulnerability is identified as CVE-2026-19939. The attack can be executed remotely. There is not any exploit available. Applying a patch is advised to resolve this issue.

Detailsinfo

A vulnerability classified as problematic has been found in Zephyr Project Zephyr up to 4.4.2. Affected is the function bt_avdtp_l2cap_disconnected of the file subsys/bluetooth/host/classic/avdtp.c of the component AVDTP Signalling Layer. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on integrity, and availability. CVE summarizes:

The AVDTP signalling layer arms a 6-second command timeout (AVDTP_TIMEOUT) in avdtp_send_cmd() whenever the local device issues an AVDTP request. Every response handler in subsys/bluetooth/host/classic/avdtp.c cancels session->timeout_work before clearing the pending request, but bt_avdtp_l2cap_disconnected() only cleared session->req and left the delayable work armed. The struct bt_avdtp session is the first member of struct bt_a2dp, whose instances live in a static per-connection array, and a2dp_get_connection() in subsys/bluetooth/host/classic/a2dp.c wipes a slot with memset() as soon as session->br_chan.chan.conn is NULL — which the L2CAP layer arranges immediately after the disconnect callback returns. A remote Bluetooth BR/EDR peer triggers the condition by opening the AVDTP signalling channel, letting the local application issue an AVDTP procedure (the standard A2DP flow issues bt_a2dp_discover() from the connected callback), then tearing the signalling channel down without responding and re-opening it within the remaining timeout window. The reconnect reaches a2dp_accept() → a2dp_get_connection(), which zeroes the whole struct bt_a2dp while the work item's struct _timeout is still linked into the kernel's global timeout list. Both the disconnect and the reconnect instants are chosen by the attacker, so no race has to be won; an encrypted BR/EDR link is required, and CONFIG_BT_A2DP (experimental) must be enabled. With the default CONFIG_TIMEOUT_BACKEND_DLIST backend the kernel decides a timeout is inactive by testing whether its list node is linked, so after the memset() the kernel treats a node that is still on the global timeout list as free: the announce path pops a node whose links and handler pointer are NULL, and the next bt_work_reschedule() on the recycled session re-inserts the same node into a list that already contains it. The consequence is corruption of the single kernel data structure every timer, timeslice and sleep depends on — writes through zeroed or stale list pointers and a NULL handler dispatch — producing a system-wide crash or hang rather than a fault confined to the A2DP session. The fix cancels session->timeout_work at the top of bt_avdtp_l2cap_disconnected() and moves k_work_init_delayable() from avdtp_send_cmd() to the session-establishment paths bt_avdtp_connect() and bt_avdtp_l2cap_accept(), so the work item is always initialized before a disconnect callback can run.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-19939 since 08/15/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available.

Applying the patch a10d18c3be9d1a968574dbfbce6baee58ea398e8 is able to eliminate this problem.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.4.0
• 4.4.1
• 4.4.2

CPE 2.3info

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CPE 2.2info

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