dbcve.org
AndroidOperating system · Google

CVE-2021-0941

MEDIUM · 6.7 CVSS v3.1 Published 2021-10-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
69/100
Remediation priority · Elevated
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
In bpf_skb_change_head of filter.c, there is a possible out of bounds read due to a use after free. This could lead to local escalation of privilege with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-154177719References: Upstream kernel

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 confidence

A use-after-free vulnerability in the bpf_skb_change_head function within the Android kernel's BPF (Berkeley Packet Filter) subsystem allows an attacker with System-level privileges to perform an out-of-bounds read, potentially leading to local privilege escalation. The bug occurs when memory is freed but still referenced, causing the kernel to read from deallocated memory locations.

MitigationApply the upstream kernel patch addressing the use-after-free in bpf_skb_change_head. For Android devices, this requires a kernel security update from the device manufacturer or through monthly security patch levels.

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
AndroidOperating 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
Local
Complexity
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:H/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. Confirm the device runs Android
    Run 'getprop ro.build.version.release' or check system settings to verify the operating system is Google Android
    Affected if The device is not running Android (the vulnerability only affects Android kernels)
  2. Identify the kernel version
    Run 'uname -r' or check /proc/version to retrieve the installed kernel version string
    Affected if The kernel version is older than the patched version for CVE-2021-0941 (compare against available security patch information for this CVE)
  3. Check if BPF subsystem is accessible
    Attempt to access BPF system call (e.g., check for /sys/kernel/debug/bpf or attempt a bpf() system call) or verify BPF is loaded via 'lsmod | grep bpf' if modules are visible
    Affected if BPF is enabled and accessible - the vulnerability exists in the bpf_skb_change_head function within the BPF subsystem, so this is required for exploitation
  4. Verify the device security patch level
    Run 'getprop ro.build.version.security_patch' to retrieve the Android security patch date
    Affected if The security patch level is earlier than the month CVE-2021-0941 was addressed in Google's Android security bulletin
  5. Check for kernel debug symbols or bpf_skb_change_head presence
    Inspect /proc/kallsyms (if accessible) or the kernel image for the symbol 'bpf_skb_change_head' to confirm the vulnerable function exists in the running kernel
    Affected if The symbol bpf_skb_change_head is present in the kernel, indicating the affected code path exists

A user is affected if the device runs Android, has an unpatched kernel version lacking the CVE-2021-0941 fix, and has the BPF subsystem accessible - verify by comparing the kernel version and security patch level against publicly available patch information for this CVE.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the upstream kernel patch addressing the use-after-free in bpf_skb_change_head. For Android devices, this requires a kernel security update from the device manufacturer or through monthly security patch levels.

Recommended fix High confidence

Android 12 (S) or later with January 2022 security patch level

  1. Check current Android version and security patch level in Settings > About Phone > Android version
  2. Identify the appropriate Android upgrade that includes the fix for CVE-2021-0941
  3. Upgrade the device to Android 12 (API 31) or later, which includes the patched kernel addressing the bpf_skb_change_head use-after-free vulnerability
  4. Verify the security patch level is January 2022 or later after upgrade
  5. For enterprise or embedded devices unable to upgrade Android, apply the upstream Linux kernel patch for BPF subsystem (if available from device vendor)
Caveat Upgrading Android major version may cause incompatibility with legacy apps or custom firmware; ensure app and carrier compatibility testing before deployment

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

Fix this in Android Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing24.0 h
  • Review / QA12.0 h
60.0 hours of engineering $10,240
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $16,384.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-0941 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-0941 in production — separate from our analysis above.

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.

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