CVE-2026-19740 — Bluetooth LE Controller: retained RX node leak and reachable assertion in the PHY Update procedure
The Link Layer Control Procedure (LLCP) implementation of the Zephyr software Bluetooth LE Controller retains the receive node that carried an accepted LL_PHY_UPDATE_IND so that it can later be reused for the host notification when the update instant is reached (llcp_rx_node_retain() in subsys/bluetooth/controller/ll_sw/ull_llcp.c, and the node is deliberately not recycled while marked NODE_RX_TYPE_RETAIN). The invalid-PDU arms of llcp_lp_pu_rx() and llcp_rp_pu_rx() in subsys/bluetooth/controller/ll_sw/ull_llcp_phy.c completed the procedure via llcp_lr_complete() / llcp_rr_complete() without first releasing that retained node, so the procedure context — the only remaining reference to the node — was freed while the node was still held out of the receive pool. A peer device on an established LE connection can drive this deterministically and without pairing or encryption. Against a peripheral it sends LL_PHY_REQ, receives LL_PHY_RSP, sends a valid LL_PHY_UPDATE_IND with an instant a few connection events in the future (so the node becomes retained), and then, before the instant is reached, sends any other LL Control PDU such as LL_LENGTH_REQ; ull_cp_rx() routes it to the active remote PHY Update procedure, which takes the invalid-PDU path. The mirror case applies to a locally initiated PHY Update followed by an LL_REJECT_IND. In the default configuration (CONFIG_BT_ASSERT and CONFIG_BT_CTLR_ASSERT_DEBUG both default y) the violated invariant in llcp_lr_check_done() / llcp_rr_check_done() triggers a controller assertion, ending in k_oops() (or k_panic()) — a single crafted PDU sequence from radio range faults the device. With those assertions compiled out, each attempt silently leaks one receive PDU node and its memq link; because the controller receive pool is small (PDU_RX_CNT, driven by CONFIG_BT_CTLR_RX_BUFFERS, which defaults to 1) and each attempt costs the attacker only a reconnect, a few repetitions exhaust the pool and leave Bluetooth inoperable until reboot. On releases v3.4.0 through v3.7.x the assertion is never reached, whatever the configuration, so every attempt leaks silently. The impact is limited to availability: the orphaned node leaves no dangling pointer that is later dereferenced and is never delivered to the host, so there is no memory corruption or information disclosure. The same pull request applies the identical release to the Connection Update and CIS-create procedures, whose invalid-PDU arms had the same omission.
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 0.1% (30-day exploitation probability)+0
- 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.
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 matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Zephyrproject | Zephyr | ≥ 3.4.0 and < 4.5.0 | 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 |
|---|---|---|---|---|---|
| 6.5 | CVSS 3.1 | Medium | 2.8 | 3.6 | vulnerabilities@zephyrproject.org via NIST National Vulnerability Database |
| 6.5 | CVSS 3.1 | Medium | — | — | zephyr via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: vulnerabilities@zephyrproject.org) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
CWE-401 · Missing Release of Memory after Effective Lifetime
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.10%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · zephyrproject/zephyr
- Source status changed · Received → Awaiting Analysis
- Record published
- CVSS changed · 6.5
- 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-2026-75083 Integer underflow of the radio-reported frame length causes an out-of-bounds write in the NXP KW41Z IEEE 802.15.4 driver 1d
- 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-2026-75085 Out-of-bounds read from received-frame length underflow in the STM32WBA 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-2026-19939 Bluetooth Classic AVDTP: stale timeout work on signalling-channel disconnect leads to kernel timeout-list corruption 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 CISA SSVC assessment.
- 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-2026-19740 is "Bluetooth LE Controller: retained RX node leak and reachable assertion in the PHY Update procedure", 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 6.5 describes technical severity. EPSS 0.10% 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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