# CVE-2026-19570: Out-of-bounds write in LE Audio Broadcast Sink when copying BASE subgroup metadata into the BASS receive state

Status: published. Published: 2026-10-09. Updated: 2026-11-04.

The LE Audio Broadcast Sink in subsys/bluetooth/audio/bap_broadcast_sink.c copies subgroup metadata from a received Basic Audio Announcement (BASE) into the static Broadcast Audio Scan Service parameter structure mod_src_param without any bounds check. In base_subgroup_meta_cb() the destination element was selected as mod_src_param.subgroups[mod_src_param.num_subgroups] with no test against ARRAY_SIZE(mod_src_param.subgroups) (sized by CONFIG_BT_BAP_BASS_MAX_SUBGROUPS, default 1), and the metadata was copied with memcpy() using the raw on-air length returned by bt_bap_base_get_subgroup_codec_meta() into a metadata array sized by CONFIG_BT_AUDIO_CODEC_CFG_MAX_METADATA_SIZE (default 4). The BASE validator bt_bap_base_get_base_from_ad() only checks structural consistency and permits up to ~24 subgroups and metadata LTVs of ~240 octets.

The defect is reached from the periodic advertising receive callback: pa_recv() → bt_data_parse() → pa_decode_base() → update_recv_state_base() → bt_bap_base_foreach_subgroup() → base_subgroup_meta_cb(). Every broadcast sink registers a scan-delegator receive state at creation (bt_bap_broadcast_sink_create() calls broadcast_sink_add_src()), and CONFIG_BT_BAP_BROADCAST_SINK depends on CONFIG_BT_BAP_SCAN_DELEGATOR, so the path is active in every broadcast-sink build once the device is periodic-advertising-synced. An attacker in radio range who operates a broadcast source the device syncs to — or who impersonates the advertiser address and SID of one already in use, periodic advertising data being unauthenticated — can change the BASE at will; each new BASE is re-parsed.

A crafted BASE therefore writes attacker-chosen bytes past the end of a fixed static object in .bss: up to roughly 236 bytes for an oversized metadata LTV, plus whole struct bt_bap_bass_subgroup records for each subgroup beyond CONFIG_BT_BAP_BASS_MAX_SUBGROUPS. This is memory corruption of adjacent Bluetooth-audio state reachable with no pairing, bonding or GATT connection, with a potential for remote code execution in the Bluetooth RX thread; in addition, the unvalidated metadata_len is forwarded to bt_bap_scan_delegator_mod_src(), which neither clamps it nor rejects it, leading to a further copy into the receive state and to out-of-bounds memory being disclosed in the BASS receive-state notification sent to a connected Broadcast Assistant.

The fix rejects a BASE carrying more subgroups than the receive state can hold (discarding the update entirely) and omits metadata that does not fit rather than copying it, and additionally honours the previously-ignored error return of the subgroup decode pass.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/zephyrproject-rtos/zephyr/commit/5738f61f4128bb38508bab57342b1f7bf218d127

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 3.6.0; < 4.5.0 (affected, semver). Source: CNA: zephyr

## Severity and prioritization

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H; source: CNA: zephyr

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H; source: NVD: vulnerabilities@zephyrproject.org

- CISA KEV: No listing in collected sources

- EPSS: 0.29% as of 2026-11-03; percentile 21.80%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-120, CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/5738f61f4128bb38508bab57342b1f7bf218d127 (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-4qwc-2qfq-w2fj (CNA: zephyr)

- https://github.com/zephyrproject-rtos/zephyr/commit/5738f61f4128bb38508bab57342b1f7bf218d127 (vulnerabilities@zephyrproject.org)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-4qwc-2qfq-w2fj (vulnerabilities@zephyrproject.org)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-19570; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19570; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-19570; retrieved 2026-11-04; source updated Not reported

Revision: 894b00791c8c943df5c0a204ddf21f1bf0ef37b8269785f6b8f68c0fee2d7592

Canonical: https://y2.dev/cve/CVE-2026-19570

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