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Esp IdfApplication · Espressif

CVE-2021-28136

MEDIUM · 6.5 CVSS v3.1 Published 2021-09-07
Fix available
A fix is available. Upgrade to after 4.4 or later.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The Bluetooth Classic implementation in Espressif ESP-IDF 4.4 and earlier does not properly handle the reception of multiple LMP IO Capability Request packets during the pairing process, allowing attackers in radio range to trigger memory corruption (and consequently a crash) in ESP32 via a replayed (duplicated) LMP packet.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The Bluetooth Classic (BR/EDR) implementation in ESP-IDF 4.4 and earlier fails to properly handle multiple LMP (Link Management Protocol) IO Capability Request packets during the pairing process. An attacker within radio range can replay or duplicate these LMP packets, triggering memory corruption that causes the ESP32 to crash.

MitigationUpgrade ESP-IDF to version 4.4.1 or later. If immediate patching is not feasible, consider disabling Bluetooth Classic functionality or implementing network-level controls to prevent unauthorized attackers from reaching devices in radio range.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Esp IdfApplication
Affected:<= 4.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify ESP-IDF version used in firmware
    Check your build system, release notes, or firmware metadata for the ESP-IDF version tag or commit hash. Compare it to the affected range: any version 4.4 or earlier.
    Affected if The ESP-IDF version is 4.4 or earlier.
  2. Verify Bluetooth Classic is enabled
    Inspect the project configuration (sdkconfig or defconfig) for CONFIG_BT_BTU_TASK_STACK_SIZE or similar Bluetooth options. Look for CONFIG_BT_BLE_ENABLED or CONFIG_BT_BR_ENABLED settings.
    Affected if CONFIG_BT_BR_ENABLED or CONFIG_BT_CLASSIC is set to y/true in the build configuration.
  3. Confirm device exposes Bluetooth Classic interface
    Check if the firmware initializes Bluetooth Classic (BR/EDR) using esp_bt_controller_init with ESP_BT_MODE_CLASSIC_BT or calls like esp_bt_codep_coded_coc_init. Review the application's Bluetooth initialization code.
    Affected if The firmware code calls esp_bt_controller_init with ESP_BT_MODE_CLASSIC_BT or enables classic Bluetooth via menuconfig.
  4. Check if device is in pairing-discoverable mode
    Monitor Bluetooth traffic or review application logs for HCI commands like HCI_IO_CAPABILITY_REQUEST. Verify the device accepts pairing requests from unknown devices.
    Affected if The device is discoverable and accepts pairing requests from any nearby attacker.

You are affected if your firmware was built with ESP-IDF 4.4 or earlier and has Bluetooth Classic (BR/EDR) enabled and exposed to unknown attackers within radio range.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 4.4
Interim mitigation

Upgrade ESP-IDF to version 4.4.1 or later. If immediate patching is not feasible, consider disabling Bluetooth Classic functionality or implementing network-level controls to prevent unauthorized attackers from reaching devices in radio range.

Recommended fix High confidence

ESP-IDF 4.4.1 or later (recommended: latest 4.4.x stable release)

  1. 1. Identify the current ESP-IDF version installed by running 'idf.py --version' or checking the 'IDF_VERSION' environment variable
  2. 2. Download the latest stable ESP-IDF release (v4.4.6 or later) from the official Espressif GitHub repository: https://github.com/espressif/esp-idf/releases
  3. 3. Back up any existing projects and custom board configurations
  4. 4. Install the new ESP-IDF version following the standard installation process for your operating system (Windows, Linux, or macOS)
  5. 5. Update the 'IDF_PATH' environment variable to point to the new installation directory
  6. 6. Run 'idf.py fullclean' on existing projects to remove cached build files
  7. 7. Rebuild and flash the application to the ESP32 device using 'idf.py build' and 'idf.py -p /dev/ttyUSB0 flash monitor'
Caveat Minimal risk; this is a patch version upgrade within the same major.minor release. Ensure any custom Bluetooth components are compatible with the updated IDF version.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Esp Idf Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-28136 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data