Zephyr Project up to 4.4.2 delayable_msg.c delayable_msg_handler race condition

Summaryinfo

A vulnerability classified as critical was found in Zephyr Project Zephyr up to 4.4.2. This vulnerability affects the function delayable_msg_handler of the file subsys/bluetooth/mesh/delayable_msg.c of the component Bluetooth Mesh Access-layer Delayable Message Queue. The manipulation results in race condition. This vulnerability is cataloged as CVE-2026-19936. The attack may be launched remotely. There is no exploit available. A patch should be applied to remediate this issue.

Detailsinfo

A vulnerability was found in Zephyr Project Zephyr up to 4.4.2. It has been classified as critical. Affected is the function delayable_msg_handler of the file subsys/bluetooth/mesh/delayable_msg.c of the component Bluetooth Mesh Access-layer Delayable Message Queue. The manipulation with an unknown input leads to a race condition vulnerability. CWE is classifying the issue as CWE-362. The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently. This is going to have an impact on availability. CVE summarizes:

The Bluetooth Mesh Access-layer delayable message queue in subsys/bluetooth/mesh/delayable_msg.c shares three intrusive lists (busy_ctx, free_ctx, free_chunks) and one k_work_delayable between two cooperative threads with no synchronization: bt_mesh_delayable_msg_manage() runs on the Bluetooth host RX thread, while delayable_msg_handler() runs on the system workqueue. Both block while the lists are in an intermediate state — the enqueuer in bt_rand(), both in bt_mesh_access_send() — which lets the other context observe torn state. delayable_msg_handler() used the result of sys_slist_get() on busy_ctx without a NULL check, and allocate_delayable_msg_ctx() tested sys_slist_is_empty() and then assumed a separate sys_slist_get() would succeed. Because CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG and CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CTX_ENABLED default to y, every model response to a received mesh message is parked on this queue, so the enqueuer runs as a direct consequence of inbound traffic. A peer that can get access-layer messages accepted by a model (it must hold the NetKey and a bound AppKey, so a legitimate or compromised network member) controls the arrival rate, the size of the elicited responses and the destination address, and thereby controls occupancy of the 4-entry context pool and the 40-entry chunk pool. Exhausting the chunk pool forces bt_mesh_delayable_msg_manage() down the purge path, which sends and releases the only queued message and leaves busy_ctx empty while the delayable work item is still armed; if the enqueuer then yields, the handler runs against the empty list. The result is a read-modify-write through a NULL-based pointer (pending_msg->fired_time += 10) at a fixed low address on the system workqueue thread. On typical targets that faults, aborting the system workqueue thread — which stops all workqueue-driven functionality, including the mesh timing machinery — or resetting the node, so the impact is loss of availability of the affected node. The write value and address are fixed and no attacker-controlled length or index is involved, so this is not exploitable for memory corruption or code execution. The same unsynchronized window also allowed one message context to be selected and released by two contexts at once, producing duplicated transmissions, duplicated send-completion callbacks and crossed chunk ownership. The fix serializes every list mutation with a k_spinlock that is never held across a blocking call, makes push_msg_from_delayable_msgs() detach the queue head atomically so a message being sent is on no list, removes the unchecked sys_slist_get() from delayable_msg_handler(), and drops any message that reaches the front of the queue while the stack is suspended or reset.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-19936 since 08/15/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Technical details are known, but there is no available exploit.

Applying the patch 0a6da68955f454edc41e4b916e05c3b974209fe4 is able to eliminate this problem.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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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Entryinfo

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