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Ac6901 FirmwareOperating system · Zh Jieli

CVE-2021-31612

MEDIUM · 6.5 CVSS v3.1 Published 2021-09-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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 on Zhuhai Jieli AC690X devices does not properly handle the reception of an oversized LMP packet greater than 17 bytes during the LMP auto rate procedure, allowing attackers in radio range to trigger a deadlock via a crafted 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 · moderate confidence

The Bluetooth Classic implementation on Zhuhai Jieli AC690X devices contains a vulnerability in the LMP (Link Manager Protocol) auto rate procedure where it fails to properly handle oversized LMP packets exceeding 17 bytes. An attacker within radio range can send a crafted LMP packet that triggers a deadlock in the device, causing denial of service.

MitigationContact Zhuhai Jieli for a firmware update that properly validates LMP packet length before processing in the auto rate procedure. If no update is available, replace affected devices with alternative hardware that receives vendor security support.

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
Ac6901 FirmwareOperating system
Affected:all versions
Ac690n FirmwareOperating system
Affected:all versions
Ac692n FirmwareOperating system
Affected:all versions
Ac6902 FirmwareOperating system
Affected:all versions
Ac6903 FirmwareOperating system
Affected:all versions
Ac6905 FirmwareOperating system
Affected:all versions
Ac6904 FirmwareOperating system
Affected:all versions
Ac6907 FirmwareOperating system
Affected:all versions

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 the Bluetooth chipset model
    Examine device documentation, FCC filing, or product specifications for the Bluetooth chipset. Check the mainboard or chip markings if physical access is available. Look for 'Zh Jieli' or 'Jieli' branding along with AC690X series identifiers (6901, 690n, 692n, 6902, 6903, 6905, 6904, 6907).
    Affected if The device uses any Zhuhai Jieli AC690X chipset variant (6901, 690n, 692n, 6902, 6903, 6905, 6904, or 6907).
  2. Confirm firmware version if accessible
    If firmware is accessible via UART, debug port, or manufacturer tooling, retrieve the firmware version string. Compare against known version numbers from the vendor. Note: CVE states all versions are affected.
    Affected if Firmware version string corresponds to any release of the listed AC690X chips.
  3. Verify Bluetooth Classic (BR/EDR) is enabled
    Check device Bluetooth settings or configuration. Confirm the device operates in Bluetooth Classic mode (not BLE-only). The vulnerability affects LMP (Link Manager Protocol) which is specific to Classic Bluetooth.
    Affected if Bluetooth Classic (BR/EDR) is enabled and actively advertising or connected.
  4. Check for LMP auto rate feature
    Inspect Bluetooth stack configuration or firmware build options for LMP auto rate procedure settings. This is typically a vendor-specific feature in the Bluetooth firmware of these chipsets.
    Affected if LMP auto rate procedure is enabled in the Bluetooth stack configuration.

A device is affected if it contains any Zhuhai Jieli AC690X chipset variant (6901, 690n, 692n, 6902, 6903, 6905, 6904, or 6907) with Bluetooth Classic enabled, as all firmware versions of these chips contain the vulnerable LMP auto rate procedure.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Contact Zhuhai Jieli for a firmware update that properly validates LMP packet length before processing in the auto rate procedure. If no update is available, replace affected devices with alternative hardware that receives vendor security support.

Fix this in Ac6901 Firmware Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,380
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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-2021-31612 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
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  • Version or environment caveats, and links to real fixes
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