CVE Intelligence
Medium Memory corruption

CVE-2026-77684 — Bluetooth Classic HFP Hands-Free: TX buffer leak on RFCOMM disconnect leads to permanent Bluetooth denial of service

The Bluetooth Classic Hands-Free Profile HF role in subsys/bluetooth/host/classic/hfp_hf.c does not release the AT command buffers that are still queued on hf->tx_pending when the RFCOMM DLC goes down. hfp_hf_disconnected() only cancelled the work items and cleared hf->acl, and no other code path ever dequeues those buffers, so each one is permanently lost from the fixed hf_pool (CONFIG_BT_MAX_CONN + 1 buffers, i.e. two in the default configuration). The same function also left BT_HFP_HF_FLAG_CONNECTED set, and hfp_hf_create() wiped the object with memset() as soon as hf->acl was NULL, without checking whether hf->work, hf->slc_work or hf->deferred_work was still pending or running. The remote Audio Gateway peer controls the trigger end to end and needs no application involvement: an unsolicited +BCS: 1 response makes bcs_handle() call bt_hfp_hf_select_codec() and queue an AT+BCS buffer, which cannot be transmitted while BT_HFP_HF_FLAG_RX_ONGOING is set, and an immediately following RFCOMM DISC strands that buffer. Repeating the connect / +BCS / disconnect cycle a couple of times empties hf_pool for good. With the pool exhausted, HFP command sending fails permanently, and because hfp_hf_send_cmd() allocates with K_FOREVER (bt_rfcomm_create_pdu() → bt_conn_create_pdu()) from the Bluetooth RX context — where that timeout is not downgraded to K_NO_WAIT — one further +BCS from the peer parks the Bluetooth RX thread inside net_buf_alloc() with no possible waker, halting all HCI event processing until the device is rebooted. Separately, reusing the HF slot while a work handler was still queued or running allowed memset() to wipe live k_work items out from under the system workqueue, corrupting shared kernel workqueue state. Exploitation requires an established HFP session (for SSP devices L2CAP enforces authentication before the RFCOMM channel is reachable) and a build with CONFIG_BT_HFP_HF enabled.

Published Oct 19, 2026 · Updated Oct 19, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: zephyr

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • 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.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
—
No EPSS score.
Affects
Zephyrproject
Zephyr
CVSS base
5.7
Medium · 2 source(s)

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.

  1. Identify exposed assets running the affected vendor/product/version combinations (Zephyrproject Zephyr).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. 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.

VendorProductVersionsStatusSource
Zephyrproject Zephyr ≥ 4.2.0 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.

Attack vector
Adjacent
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.7 CVSS 3.1 Medium 2.1 3.6 vulnerabilities@zephyrproject.org via NIST National Vulnerability Database
5.7 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: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

Other CVEs with this weakness →

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.
endpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · zephyrproject/zephyr
    Oct 19, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 19, 2026
  • CVSS changed · 5.7
    Oct 19, 2026 · NIST National Vulnerability Database
  • Source status changed · → Received
    Oct 19, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 19, 2026 · Alertas do Telegram
  • CVE published
    Oct 19, 2026 · zephyr

Source activity

Repeated readings are counted rather than listed.

  • 1× References added · Oct 19, 2026 – Oct 19, 2026
  • 1× Official description updated · Oct 19, 2026 – Oct 19, 2026

References

2 on the record

Elsewhere on this site

Zephyrproject
every CVE for this vendor
Memory corruption
same class
CWE-401
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-19595 Zephyr RTIO syscall verifier validates output parameters for read instead of write access 4h
  • CVE-2026-76788 Stack out-of-bounds write in the OSDP Control Panel reply parser 6h
  • CVE-2026-76787 NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum 6h
  • 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 5d
  • CVE-2026-75084 Out-of-bounds write in the TI CC1200 IEEE 802.15.4 driver from an unvalidated radio-supplied packet length 5d
  • CVE-2026-75085 Out-of-bounds read from received-frame length underflow in the STM32WBA IEEE 802.15.4 driver 5d

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 FIRST EPSS score.
  • 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-2026-77684 is "Bluetooth Classic HFP Hands-Free: TX buffer leak on RFCOMM disconnect leads to permanent Bluetooth denial of service", 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 5.7 describes technical severity. 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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