CVE-2021-28135
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 · uneditedThe Bluetooth Classic implementation in Espressif ESP-IDF 4.4 and earlier does not properly handle the reception of continuous unsolicited LMP responses, allowing attackers in radio range to trigger a denial of service (crash) in ESP32 by flooding the target device with LMP Feature Response data.
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 confidenceThe ESP-IDF Bluetooth Classic implementation fails to properly handle continuous unsolicited LMP (Link Management Protocol) Feature Response messages. An attacker within radio range can flood an ESP32 device with these LMP responses, causing a buffer overflow or resource exhaustion that leads to a system crash.
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<= 4.4CVSS 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 checksWork through these to decide whether this CVE applies to you.
-
Identify if the device runs ESP-IDFInspect the firmware or device documentation to confirm it uses Espressif ESP-IDF as the development frameworkAffected if The device firmware is not based on ESP-IDF, then this CVE does not apply
-
Determine the ESP-IDF versionCheck the firmware version string, build metadata, or bootloader information to identify the ESP-IDF versionAffected if The installed ESP-IDF version is 4.4 or earlier, placing it within the vulnerable range
-
Confirm Bluetooth Classic is enabledExamine the device Bluetooth configuration, runtime settings, or device capabilities to determine if Classic Bluetooth (BR/EDR) is active versus only BLEAffected if Bluetooth Classic is not in use, only BLE (Bluetooth Low Energy) is enabled, then the device is not affected by this specific LMP vulnerability
A device is affected if it runs ESP-IDF version 4.4 or earlier AND has Bluetooth Classic (BR/EDR) functionality enabled, making it susceptible to the LMP feature response overflow via nearby attackers.
Generated from the published advisory. Verify against your own configuration.
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 · scopedUpdate ESP-IDF to a version newer than 4.4 that contains the fix for this vulnerability. If immediate updating is not feasible, consider disabling Bluetooth Classic functionality if not required, or implement network-level controls to limit exposure to nearby attackers.
ESP-IDF > 4.4 (check Espressif's release notes for the specific version containing the LMP fix)
- Upgrade ESP-IDF to a version newer than 4.4 that contains the fix for the LMP Feature Response handling vulnerability
- Ensure the Bluetooth Classic stack is updated in the new ESP-IDF version
- Rebuild and deploy the application with the updated ESP-IDF
- Test the device to verify Bluetooth Classic functionality operates normally without crashes
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28135 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-28135 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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