CVE-2021-34147
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 the Cypress WICED BT stack through 2.9.0 for CYW20735B1 does not properly handle the reception of a malformed LMP timing accuracy response followed by multiple reconnections to the link slave, allowing attackers to exhaust device BT resources and eventually trigger a crash via multiple attempts of sending a crafted LMP timing accuracy response followed by a sudden reconnection with a random BDAddress.
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 confidenceThe Cypress WICED BT stack through 2.9.0 on CYW20735B1 fails to properly handle malformed LMP (Link Manager Protocol) timing accuracy response packets combined with rapid reconnections using random BDAddresses. This specific sequence exhausts Bluetooth device resources (likely connection slots, memory buffers, or state machine entries) leading to a denial-of-service 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<= 2.9.0CVSS 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
- 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.
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Identify Cypress WICED BT stack productDetermine if the device uses Cypress WICED BT stack on CYW20735B1 hardware by reviewing product documentation, firmware build files, or system information that lists the Bluetooth controller and stack provider.Affected if The device does not use Cypress WICED BT stack on CYW20735B1 hardware - this CVE does not apply.
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Check WICED BT stack versionLocate the WICED BT stack version in firmware metadata, boot logs, or Bluetooth stack configuration files. Common locations include version strings in firmware binaries, SDK documentation, or stack initialization logs.Affected if The installed WICED BT stack version is 2.9.0 or lower, or if the version cannot be determined and the product is confirmed as using WICED BT stack.
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Verify Bluetooth functionality is enabledCheck if Bluetooth is actively enabled on the device by reviewing system services, Bluetooth daemon status, or application configuration that controls Bluetooth stack initialization.Affected if Bluetooth is disabled at the hardware or software layer - the vulnerability cannot be triggered without active Bluetooth operation.
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Review crash logs and failure reportsExamine system logs, crash dumps, or error logs for Bluetooth-related crashes, unexpected reboots, or LMP protocol errors occurring during connection attempts, particularly after rapid reconnection sequences.Affected if Crash logs show Bluetooth stack crashes correlating with connection events, or memory/resource exhaustion indicators in the Bluetooth subsystem.
The environment is affected if it uses Cypress WICED BT stack version 2.9.0 or lower on CYW20735B1 hardware with Bluetooth enabled, and exhibits Bluetooth crashes during rapid reconnection patterns.
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.
From vendor dataContact Cypress for a firmware/stack update to version 2.9.0 or later that addresses this LMP handling flaw. If no update is available, implement application-layer connection rate limiting and monitor for rapid reconnection patterns as a compensating control.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34147 — 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-2021-34147 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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