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ZephyrOperating system · Zephyrproject

CVE-2021-3966

HIGH · 8.8 CVSS v3.1 Published 2023-01-11
Fix available
A fix is available. Upgrade to 3.0.0 or later.
See remediation →
93/100
Remediation priority · Urgent
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
usb device bluetooth class includes a buffer overflow related to implementation of net_buf_add_mem.

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

A buffer overflow vulnerability exists in the USB device Bluetooth class implementation within the Linux kernel, specifically in the net_buf_add_mem function. This memory corruption issue could allow a physically proximate attacker or malicious USB Bluetooth device to trigger the overflow, potentially leading to code execution or denial of service. The vulnerability affects the kernel's handling of Bluetooth device communication buffers.

MitigationApply available kernel security patches or update to a patched kernel version; restrict physical access to USB ports and disable Bluetooth if not required to reduce attack surface.

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
ZephyrOperating system
Affected:< 3.0.0

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 OS/RTOS in use
    Determine if the target system is running Zephyr RTOS (a real-time operating system) rather than a standard Linux kernel. Zephyr is typically used in embedded IoT devices, microcontrollers, and specialized hardware.
    Affected if The system is running Zephyr RTOS (not standard Linux kernel)
  2. Check Zephyr version
    Locate and inspect the Zephyr kernel version file or build configuration. This is typically found in the build output, kernel image metadata, or version header file (often in zephyr/include/version.h or displayed at boot).
    Affected if Zephyr version is less than 3.0.0 (any version 1.x or 2.x)
  3. Verify USB device Bluetooth support is enabled
    Examine the Zephyr build configuration (prj.conf or defconfig) for CONFIG_USB_DEVICE_BLUETOOTH or similar USB Bluetooth class configuration options. Also check if CONFIG_BLUETOOTH and CONFIG_USB_DEVICE are enabled.
    Affected if USB device Bluetooth support (CONFIG_USB_DEVICE_BLUETOOTH) is enabled in the build configuration
  4. Confirm net_buf_add_mem usage in Bluetooth USB path
    Inspect the Zephyr kernel source code or binary to determine if the net_buf_add_mem function is being called within the USB Bluetooth device driver path. This typically involves examining the USB Bluetooth host/client implementation files.
    Affected if The net_buf_add_mem function handles Bluetooth buffers in the USB device communication path

A system is affected if it is running Zephyr RTOS version below 3.0.0 with USB device Bluetooth support enabled and the net_buf_add_mem function used in the Bluetooth USB data path.

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 3.0.0 or later
Fixed in 3.0.0
Interim mitigation

Apply available kernel security patches or update to a patched kernel version; restrict physical access to USB ports and disable Bluetooth if not required to reduce attack surface.

Recommended fix Moderate confidence

Zephyr 3.0.0

  1. Upgrade Zephyr RTOS to version 3.0.0 or later to resolve the heap-based buffer overflow vulnerability in the USB device bluetooth class related to net_buf_add_mem
  2. After upgrading, verify the USB bluetooth functionality works correctly and test for any regressions
Caveat Major version upgrades in Zephyr may introduce breaking API changes, device tree configuration updates, or Kconfig changes that require code adjustments

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

Fix this in Zephyr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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Scan for this in your stack

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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-2021-3966 in production — separate from our analysis above.

No notes yet

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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