Zephyr Project up to 4.4.x AVRCP avrcp.c avrcp_disconnected denial of service

Summaryinfo

A vulnerability was found in Zephyr Project Zephyr up to 4.4.x and classified as critical. This issue affects the function avrcp_disconnected of the file subsys/bluetooth/host/classic/avrcp.c of the component AVRCP. Such manipulation leads to denial of service. This vulnerability is referenced as CVE-2026-85033. It is possible to launch the attack remotely. No exploit is available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Zephyr Project Zephyr up to 4.4.x. It has been rated as critical. Affected by this issue is the function avrcp_disconnected of the file subsys/bluetooth/host/classic/avrcp.c of the component AVRCP. The manipulation with an unknown input leads to a denial of service vulnerability. Using CWE to declare the problem leads to CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. Impacted is confidentiality, integrity, and availability. CVE summarizes:

The AVRCP Target role in subsys/bluetooth/host/classic/avrcp.c keeps its vendor-dependent response transmit state in a per-connection object selected by connection index (get_avrcp_tg()), with the per-transfer context (tid, sent_len, and the BT_AVRCP_TG_FLAG_TX_ONGOING flag) stored in the user_data of the queued response net_buf. The AVCTP teardown handler avrcp_disconnected() did not cancel tg->vd_rsp_tx_work and did not release the buffers still queued on tg->vd_rsp_tx_pending, so a link drop in the middle of a fragmented response left the buffer on the list with TX_ONGOING still set. A remote AVRCP Controller can trigger this deterministically: it issues a vendor-dependent command whose response exceeds one AVRCP fragment (for example GetElementAttributes or GetCapabilities), lets bt_avrcp_tg_vendor_tx_work() emit the START fragment, and then drops the ACL link instead of sending REQUEST_CONTINUING_RESPONSE. The AVCTP control channel requires an encrypted BR/EDR link (BT_SECURITY_L2), so the attacker must be a paired peer within radio range; no user interaction is needed. Because the Target objects are static and reused, the next connection landing on the same connection index finds the stale buffer at the head of vd_rsp_tx_pending. Every run of the TX work sees TX_ONGOING and returns immediately, so all further vendor-dependent responses queue behind the stale head and are never sent — a persistent loss of AVRCP Target function that no timeout clears and only a reboot recovers. Each cycle also leaks one response buffer from a shallow application pool, and a new peer that sends REQUEST_CONTINUING_RESPONSE clears the stale TX_ONGOING via bt_avrcp_tg_process_continuing_cmd(), causing the un-sent remainder of the previous peer's response to be transmitted to it. The fix cancels tg->vd_rsp_tx_work and unrefs every buffer on tg->vd_rsp_tx_pending in avrcp_disconnected(); since the TX context lives in the buffer user_data, releasing the buffers also resets the TX state machine. There is no memory corruption: the pre-fix buffer is leaked with a live reference, so no use-after-free arises.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-85033 since 09/02/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 4.5.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

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