CVE-2026-81508

Executive Summary

CVE-2026-81508 is an out-of-bounds read (CWE-125) in the BlueDroid A2DP sink implementation within Espressif's ESP-IDF (Espressif IoT Development Framework), affecting versions 5.5.5, 6.0.1, and 6.1. A paired BR/EDR audio source within radio range can send a malformed A2DP media packet that causes the function btc_a2dp_sink_handle_inc_media() to read a timestamp field before validating that the packet layout actually contains that field, resulting in an out-of-bounds read into adjacent heap memory. Impact is limited to information disclosure of heap contents over an adjacent (Bluetooth radio) attack vector; arbitrary memory disclosure and code execution are explicitly not established.

Technical Analysis

ESP-IDF is Espressif's official development framework for ESP32-class IoT silicon. The affected component is BlueDroid, the Classic Bluetooth (BR/EDR) host stack, specifically the A2DP sink role. A2DP (Advanced Audio Distribution Profile) is the Bluetooth profile used to stream audio from a source device (e.g., a phone) to a sink device (e.g., a speaker or headset).

The vulnerability resides in the media packet handling path. The function btc_a2dp_sink_handle_inc_media() processes an incoming A2DP media buffer. According to the NVD description, the function reads a timestamp field from the received media buffer before validating that the packet layout contains that field. This ordering defect is the core flaw: validation occurs after the read, so a packet whose layout does not include the timestamp field still causes the code to read the field's expected offset, advancing past the intended buffer boundary into adjacent heap memory.

A2DP media packets carry RTP-style headers including sequence numbers and timestamps, and the layout of a media packet is not guaranteed by the profile to always contain every optional field the sink may expect. A malformed packet — one crafted so that the timestamp field is absent or the buffer is shorter than the offset the code reads from — triggers the out-of-bounds read. Because the read targets adjacent heap memory, the bytes read are copied or otherwise consumed by the sink's processing path, enabling limited disclosure of heap contents to the attacking source device (or observable through the sink's behavior/diagnostics, depending on how the consumed value is surfaced).

Two important scope limits, stated in the source data, must be preserved:

• The disclosure is of adjacent heap memory and is described as "limited."
• Arbitrary memory disclosure and code execution are not established.

This is an information-disclosure-class issue, not a memory-corruption primitive. There is no evidence of a write, a controllable offset in a dangerous direction beyond the read, or a return-address/pointer corruption path. The CVSS vector confirms this: AV:A (adjacent, i.e., Bluetooth radio range), AC:L, PR:N, UI:N, S:U, C:L (low confidentiality impact), I:N, A:N.

The attack surface requires a build in which BlueDroid Classic Bluetooth and A2DP sink support are enabled, and requires a paired BR/EDR audio source within radio range. Pairing is a meaningful precondition — it limits the attacker population to devices that have completed BR/EDR pairing with the target. No public PoC, Nuclei template, or exploit code is available, and no patch evidence exists from tracked sources.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred at the vulnerability-class level (out-of-bounds read via missing pre-validation) from the NVD description and must not be read as a verified exploit recipe.

1. Reconnaissance / target identification. An attacker identifies an ESP-IDF-based device that exposes a Classic Bluetooth (BR/EDR) A2DP sink. This can be done by scanning for discoverable BR/EDR devices advertising A2DP sink service records, or by targeting a device already known to be an audio sink (speaker, headset, infotainment/audio peripheral). The attacker must be within Bluetooth radio range (adjacent-vector). No authentication on the media stream itself is required beyond an established pairing.

2. Triggering the flaw class. The attacker must be a paired BR/EDR audio source to the target. Once paired, the attacker acts as an A2DP source and sends a malformed A2DP media packet whose layout omits/deforms the timestamp field. Because btc_a2dp_sink_handle_inc_media() reads the timestamp field before validating that the packet layout contains it, the sink reads at an offset beyond the intended buffer boundary into adjacent heap memory. The packet is malformed specifically with respect to layout/length, not with respect to any write primitive.

3. Payload/execution method (class level). There is no code-execution payload in the established impact. The "payload" is the malformed media packet itself; the outcome is an out-of-bounds read. Any exfiltration of the read bytes would depend on how the sink surfaces or forwards the parsed media data, and the source data characterizes the disclosure as limited heap contents, not arbitrary memory content. No reliable, attacker-directed read offset or full memory-read primitive is established.

4. Post-exploitation impact. The realistic post-exploitation outcome is limited heap information disclosure. Heap contents on an IoT audio device could include pointers, buffer metadata, or other resident data, which may aid further exploitation research but does not by itself yield control-flow hijack. The source data explicitly states arbitrary memory disclosure and code execution are not established, so post-exploitation impact must be scoped to low-confidentiality leakage.

Impact Assessment

Business impact is bounded and low-to-moderate. The CVSS v3.1 base score is 4.3 (Medium), vector CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N. Interpretation of each subscore for this CVE:

• AV:A (Adjacent): exploitation requires proximity within Bluetooth BR/EDR radio range — physical/logical adjacency, not internet reachability. This substantially reduces the exposed population.
• AC:L (Low): no special conditions beyond a malformed packet; the flaw is in the ordering of validation.
• PR:N (None) / UI:N (None): no additional privileges or user interaction are assumed in the metric — though in practice a paired BR/EDR source is a precondition per the description.
• S:U (Unchanged): impact is confined to the vulnerable component.
• C:L (Low): limited disclosure of heap contents.
• I:N / A:N: no integrity or availability impact established.

Blast radius: ESP-IDF-based devices built with BlueDroid Classic Bluetooth and A2DP sink support enabled, on versions 5.5.5, 6.0.1, and 6.1. This includes audio-centric IoT products (speakers, soundbars, wearables with audio, audio-enabled appliances). Devices using BLE-only stacks or not enabling A2DP sink are out of scope. Because the issue is information-disclosure-only and requires pairing plus proximity, enterprise operational risk is concentrated in edge/IoT fleets with Bluetooth audio features, and in environments where heap leakage could be chained with other bugs. EPSS is not yet scored by FIRST.org; no EPSS value is asserted here. CVE is not in CISA KEV, and no exploit code or PoC is public.

Detection Guidance

Detection options are constrained because the trigger is a malformed Bluetooth media packet over a radio link, and no exploit artifacts are public. The following rules are best-effort detections for build/config exposure, vulnerable-code presence, and anomalous A2DP behavior; they are not signature-verified against a known exploit.

Sigma Rule

title: ESP-IDF BlueDroid A2DP Sink Configuration Exposure (CVE-2026-81508)
id: 6f2a9c14-3b7e-4d21-9a08-esp-idf-a2dp-81508
status: experimental
description: Detects ESP-IDF builds or logs indicating BlueDroid Classic Bluetooth with A2DP sink support enabled, the preconditions for CVE-2026-81508. This is a configuration/exposure detection, not a behavioral exploit signature.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-81508
author: valtersit.com Threat Intelligence
date: 2026/01/01
logsource:
  product: linux
  service: syslog
detection:
  selection_bt:
    - "CONFIG_BT_CLASSIC_ENABLED"
    - "CONFIG_BT_A2DP_ENABLE"
    - "btc_a2dp_sink_handle_inc_media"
    - "A2DP sink"
    - "Bluedroid"
  selection_err:
    - "out-of-bounds"
    - "heap"
  condition: selection_bt
falsepositives:
  - Legitimate device boot logs enumerating Bluetooth config
level: informational
tags:
  - cve.2026.81508
  - cwe.125

YARA Rule

rule CVE_2026_81508_ESF_IDF_A2DP_SINK_OOB_READ
{
    meta:
        description = "Detects ESP-IDF BlueDroid A2DP sink build string / symbol associated with CVE-2026-81508"
        author = "valtersit.com Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-81508"
        cve = "CVE-2026-81508"
        date = "2026-01-01"

    strings:
        $sym1 = "btc_a2dp_sink_handle_inc_media" ascii
        $sym2 = "btc_a2dp_sink_handle_inc_media" wide
        $cfg1 = "CONFIG_BT_A2DP_ENABLE" ascii
        $cfg2 = "CONFIG_BT_CLASSIC_ENABLED" ascii
        $ver1 = "ESP-IDF" ascii
        $ver2 = "v5.5.5" ascii
        $ver3 = "v6.0.1" ascii

    condition:
        uint16(0) == 0x5A4D or $sym1 or $sym2 or
        (2 of ($cfg*)) or ($ver1 and any of ($ver2, $ver3))
}

Suricata IDS Rule

Note: A2DP media travels over L2CAP/Bluetooth, which is not visible to standard IP-based Suricata inspection unless Bluetooth traffic is being bridged/encapsulated. The rule below targets any gateway or tap that exposes A2DP media over an IP encapsulation; it is a structural placeholder for malformed/short A2DP media frames rather than a verified exploit signature.

alert udp any any -> any any (msg:"CVE-2026-81508 Possible Malformed A2DP Media Packet (OOB Read Attempt)"; flow:to_server; content:"|80 60|"; depth:2; byte_test:2,<,13,2,relative; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-recon; reference:cve,2026-81508; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-81508; sid:9008151; rev:1;)

Elastic Detection

sequence by process.entity_id with maxspan=30s
  [ process where process.name == "idf.py" and process.args : "*a2dp*" ]
  [ file where file.name : "*sdkconfig*" and file.Ext.content : ("CONFIG_BT_CLASSIC_ENABLED=y" or "CONFIG_BT_A2DP_ENABLE=y") ]
| keep process.entity_id, process.name, file.name, file.path, host.name

Splunk SPL Query

index=* (sourcetype=syslog OR sourcetype=esp_idf OR sourcetype=bluetooth)
("btc_a2dp_sink_handle_inc_media" OR "A2DP sink" OR "CONFIG_BT_A2DP_ENABLE" OR "Bluedroid")
| stats count values(_raw) as events by host
| where count > 0
| table host count events

Wazuh OSSEC Rule

<group name="esp-idf,cve_2026_81508,">
  <rule id="100815" level="3">
    <decoded_as>syslog</decoded_as>
    <match>btc_a2dp_sink_handle_inc_media</match>
    <description>CVE-2026-81508: ESP-IDF BlueDroid A2DP sink vulnerable code path referenced in logs</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
  <rule id="100816" level="5">
    <decoded_as>syslog</decoded_as>
    <match>CONFIG_BT_A2DP_ENABLE</match>
    <description>CVE-2026-81508: ESP-IDF build has A2DP sink enabled (exposed to adjacent OOB read)</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations

   • Where the A2DP sink feature is not required, disable BlueDroid Classic Bluetooth and/or A2DP sink support in the build (e.g., the relevant CONFIG_BT_* toggles) and rebuild firmware. This removes the vulnerable code path from the deployed image.
   • Tighten Bluetooth pairing policy: do not leave devices pairable/discoverable beyond necessary windows; unpair untrusted sources. Note that the flaw requires a paired BR/EDR source, so controlling pairing directly limits exposure.
   • Reduce contiguous heap exposure for adjacent-attacker data by treating heap contents as potentially readable; avoid co-locating high-value secrets (keys, tokens, credentials) in the same heap region as Bluetooth audio buffers where feasible.
   • Monitor for anomalous A2DP media packets from sources; log and alert on malformed-packet handling errors in the Bluetooth stack if the build surfaces them.

2. Patch/upgrade steps

   • No vendor fix is available per tracked sources. Monitor Espressif's ESP-IDF security advisories and release notes for 5.5.x, 6.0.x, and 6.1 for a patched build, and upgrade to the first version that corrects the validation ordering in btc_a2dp_sink_handle_inc_media().
   • Until a patch is published, pin to a build configuration without A2DP sink if the feature is non-essential.

3. Long-term hardening

   • Adopt provisioning and pairing controls for BR/EDR (restrict discoverability, use bonding with enforced counterparty policy).
   • Integrate ESP-IDF SBOM tracking into firmware CI so affected versions and enabled Bluetooth profiles are inventoried across the fleet.
   • Require input-length validation before field access as a coding standard for Bluetooth stack parsing code; track upstream commits that add layout validation.
   • Maintain a Bluetooth-capable edge/IoT asset inventory and apply update cadence to firmware at the fleet level once a fix is available.

References

• NVD — CVE-2026-81508: https://nvd.nist.gov/vuln/detail/CVE-2026-81508
• Espressif ESP-IDF security advisories (vendor): https://github.com/espressif/esp-idf/security/advisories
• Espressif ESP-IDF releases (track patched versions for 5.5.x, 6.0.x, 6.1): https://github.com/espressif/esp-idf/releases
• CWE-125, Out-of-bounds Read: https://cwe.mitre.org/data/definitions/125.html
• CISA Known Exploited Vulnerabilities catalog (CVE-2026-81508 not listed at time of writing): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2026-81508 in the available data. EPSS has not yet scored this CVE. No public PoC or exploit code exists.