CVE-2021-3431
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 · uneditedAssertion reachable with repeated LL_FEATURE_REQ. Zephyr versions >= v2.5.0 contain Reachable Assertion (CWE-617). For more information, see https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-7548-5m6f-mqv9
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 · moderate confidenceIn Zephyr RTOS v2.5.0 and later, a reachable assertion vulnerability exists where an attacker can trigger an assertion failure by sending repeated LL_FEATURE_REQ (Link Layer Feature Request) packets. This is a Bluetooth Low Energy (BLE) layer vulnerability that could lead to denial of service via application 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>= 2.5.0, < 2.6.0CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/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.
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Identify Zephyr RTOS versionLocate the Zephyr version file in your build (typically zephyr/version.h or check the west.yml / manifest file) and note the version numberAffected if The installed version is >= 2.5.0 and < 2.6.0
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Confirm BLE stack is enabledCheck your Kconfig configuration for CONFIG_BT=y or CONFIG_BT_CTLR=y setting, which enables the Bluetooth Low Energy stackAffected if Bluetooth (BT) or BLE controller configuration is enabled in the build
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Verify BLE controller is in useCheck for CONFIG_BT_CTLR in Kconfig - this indicates the BLE controller (LL layer) is compiled into the firmwareAffected if CONFIG_BT_CTLR is set, meaning the vulnerable BLE controller code is present
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Check if device exposes BLE advertising or accepts connectionsInspect your application code for bt_enable() calls and BLE peripheral/advertising role initialization (e.g., bt_le_adv_start, bt_gatt_service_register)Affected if The device accepts BLE connections or responds to LL_FEATURE_REQ packets
You are affected if your Zephyr version is between 2.5.0 and 2.6.0, BLE controller is enabled, and the device accepts BLE connections where it could receive repeated LL_FEATURE_REQ packets.
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 · scoped2.6.0
Upgrade Zephyr to a version containing the patch for this vulnerability, or apply the specific code fix to handle repeated LL_FEATURE_REQ requests without triggering an assertion. If upgrading is not feasible, implement input validation or rate limiting on BLE connection requests.
Zephyr 2.6.0 or later
- 1. Backup your current Zephyr project and configuration
- 2. Update the Zephyr SDK or toolchain to a version compatible with Zephyr 2.6.0
- 3. Fetch Zephyr version 2.6.0 or later: `git fetch` and `git checkout v2.6.0` or clone the desired version
- 4. Update the West manifest file (west.yml) to pin to Zephyr version 2.6.0 or later
- 5. Run `west update` to synchronize all repositories to the new versions
- 6. Rebuild your application with the new Zephyr version
- 7. Test the application thoroughly to verify functionality and compatibility
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-3431 — 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-2021-3431 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
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- Version or environment caveats, and links to real fixes
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