CVE-2026-19939 — Bluetooth Classic AVDTP: stale timeout work on signalling-channel disconnect leads to kernel timeout-list corruption
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.2% (30-day exploitation probability)+1
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Zephyrproject Zephyr).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Zephyrproject | Zephyr | ≥ 3.7.0 and ≤ 4.4.2 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 6.3 | CVSS 3.1 | Medium | 2.1 | 4.2 | vulnerabilities@zephyrproject.org via NIST National Vulnerability Database |
| 6.3 | CVSS 3.1 | Medium | — | — | zephyr via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H (score shown at the top: vulnerabilities@zephyrproject.org) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Not enough vector or weakness data: use the affected application’s logs as a starting point.
Timeline
What happened to this CVE, newest first.
- 2026
- SSVC assessment updated
- Affected products added · zephyrproject/zephyr
- Source status changed · Received → Awaiting Analysis
- Record published
- CVSS changed · 6.3
- Source status changed · → Received
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
2 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-75085 Out-of-bounds read from received-frame length underflow in the STM32WBA IEEE 802.15.4 driver 1d
- Medium CVE-2026-75084 Out-of-bounds write in the TI CC1200 IEEE 802.15.4 driver from an unvalidated radio-supplied packet length 1d
- Medium CVE-2026-75083 Integer underflow of the radio-reported frame length causes an out-of-bounds write in the NXP KW41Z IEEE 802.15.4 driver 1d
- High CVE-2026-19673 Out-of-bounds read and net_buf length underflow in Zephyr Ethernet L2 when parsing a truncated VLAN header 1d
- Medium CVE-2026-19940 Bluetooth HFP AG reuses a connection slot while a delayable work item is still armed, corrupting kernel timeout bookkeeping 2d
- Medium CVE-2026-19937 Bluetooth Mesh Access layer permanently leaks delayable-message contexts, disabling all model responses 2d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-19939 is "Bluetooth Classic AVDTP: stale timeout work on signalling-channel disconnect leads to kernel timeout-list corruption", rated Medium. It affects Zephyr (Zephyrproject); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.3 describes technical severity. EPSS 0.18% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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