---
id: CVE-2026-18748
title: >-
  Out-of-bounds read in Bluetooth Classic A2DP codec information element
  handling
summary: >-
  The Bluetooth Classic A2DP host stores a codec Information Element (IE) in
  struct bt_a2dp_codec_ie, a one-byte len field plus a fixed 8-byte codec_ie[]
  array. When an AVDTP peer sent a codec IE longer than 8 bytes,
  a2dp_process_config_in…
severity: low
cvss: 3.5
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'
cvssSource: cna
cwe:
  - CWE-125
vendor: zephyrproject
product: zephyr
affected:
  - zephyr >= 4.3.0 <= 4.4.2
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T18:19:29.937Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-18748'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/c5f649f4714e625362fbaa93ffd7419f9c27342b
    label: Fix commit
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-6qq5-25mp-x5rg
    label: GHSA-6qq5-25mp-x5rg
tags:
  - cve.org
ingestedAt: '2026-10-21T19:10:31.404Z'
---

## Overview

The Bluetooth Classic A2DP host stores a codec Information Element (IE) in struct bt_a2dp_codec_ie, a one-byte len field plus a fixed 8-byte codec_ie[] array. When an AVDTP peer sent a codec IE longer than 8 bytes, a2dp_process_config_ind() in subsys/bluetooth/host/classic/a2dp.c copied only the first 8 bytes but assigned the full, attacker-chosen length to len, and then persisted that inconsistent structure into the application's struct bt_a2dp_stream via stream->codec_config. bt_a2dp_get_config_cb() and bt_a2dp_set_config_cb() had the same truncate-the-copy-but-keep-the-length pattern.

Every later consumer trusts len. In particular the responder for an incoming AVDTP GET_CONFIGURATION, a2dp_get_config_ind(), executes net_buf_add_mem(rsp_buf, &ep->stream->codec_config.codec_ie[0], ep->stream->codec_config.len), so a paired BR/EDR peer that first sends a SET_CONFIGURATION carrying an oversized codec IE and then requests the configuration back causes the stack to read up to roughly 245 bytes past the end of the 8-byte array and transmit them in the response. codec_config is the last member of struct bt_a2dp_stream, so the read runs into memory adjacent to the application's stream object. The same inconsistency is also handed to the config_req(), reconfig_req() and get_config_rsp() application callbacks, where a natural memcpy() of len bytes performs a further out-of-bounds read.

Reaching the on-air disclosure requires CONFIG_BT_CLASSIC with CONFIG_BT_A2DP, an AVDTP peer that has completed pairing (the AVDTP L2CAP channel requires BT_SECURITY_L2), and a local endpoint registered for a non-SBC codec — BT_A2DP_MPEG1/BT_A2DP_MPEG2/BT_A2DP_ATRAC/BT_A2DP_VENDOR via BT_A2DP_EP_INIT() — because the SBC branch already pins the IE length to 4 bytes. The bt_a2dp_get_config_cb() response path has no such gate and hands the lying length to any application. There is no out-of-bounds write: the net_buf tailroom check bounds the destination, so the impact is limited to disclosure of a bounded region of adjacent RAM to the peer.

The fix replaces the hardcoded BT_A2DP_MAX_IE_LENGTH with the configurable CONFIG_BT_A2DP_CODEC_MAX_IE_LEN (default 8, range 4–253), sizes codec_ie[] from it, and rejects any received IE that exceeds it instead of silently truncating, so len can no longer exceed the number of valid bytes.

## Affected

- `zephyr >= 4.3.0 <= 4.4.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.