dbcve.org
Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 13 Jun 2022.
Linux KernelOperating system · Linux

CVE-2021-0920

MEDIUM · 6.4 CVSS v3.1 Published 2021-12-15
Fix available
A fix is available. Upgrade to after 5.13 or later.
See remediation →
96/100
Remediation priority · Urgent
In the wild 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 unix_scm_to_skb of af_unix.c, there is a possible use after free bug due to a race condition. 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-196926917References: 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 race condition in unix_scm_to_skb function of af_unix.c (Unix domain socket implementation) leads to a use-after-free vulnerability. An attacker with System-level privileges can exploit this to achieve local privilege escalation. The race occurs when handling socket control messages where the skb (socket buffer) is freed while still being referenced.

MitigationApply the upstream kernel patch for CVE-2021-0920 which addresses the race condition in unix_scm_to_skb by properly synchronizing skb lifetime management. For Android devices, this requires a kernel security update (/vendor or /boot image update).

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
Linux KernelOperating system
Affected:<= 5.13= 5.14
Debian LinuxOperating system
Affected:= 9.0
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
High
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/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. Check Linux kernel version
    Run 'uname -r' or 'cat /proc/version' to obtain the installed kernel version
    Affected if The version is 5.14.x or 5.13.x or lower (e.g., 5.13.x, 5.12.x, etc.)
  2. Verify AF_UNIX socket support
    Confirm the kernel is built with CONFIG_UNIX=y (usually default). Check via 'zcat /proc/config.gz | grep CONFIG_UNIX' or check /boot/config-$(uname -r)
    Affected if CONFIG_UNIX is enabled (standard in most Linux kernels, making the race condition exploitable if kernel version is vulnerable)
  3. Check Android version
    On Android devices, run 'getprop ro.build.version.release' or check Settings > About Phone > Android version
    Affected if Any Android version is running, as the advisory lists 'all versions' as affected
  4. Check Debian version for Debian systems
    Run 'cat /etc/debian_version' to identify the Debian release
    Affected if The system is running Debian 9.0 specifically

You are affected if your Linux kernel is version 5.14.x or any 5.13.x or lower, or if you run any version of Android, or if you run Debian 9.0, and the AF_UNIX socket interface is available in your kernel.

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 a release after 5.13
Interim mitigation

Apply the upstream kernel patch for CVE-2021-0920 which addresses the race condition in unix_scm_to_skb by properly synchronizing skb lifetime management. For Android devices, this requires a kernel security update (/vendor or /boot image update).

Recommended fix High confidence

Linux kernel 5.14.8 or later (or equivalent distribution-specific kernel update that includes the CVE-2021-0920 fix)

  1. Identify the current kernel version using 'uname -r' or 'cat /proc/version'
  2. Check if your distribution has released a security update for this CVE (e.g., for Debian 9, check security.debian.org for DLA or for mainline kernels check kernel.org
  3. For Debian 9 (stretch): Update the kernel package via 'apt update && apt list --upgradable' followed by 'apt install linux-image-<version>'
  4. For upstream kernels: Upgrade to Linux kernel 5.14.8 or later (this version contains the upstream fix for this CVE)
  5. Reboot the system to load the fixed kernel: 'systemctl reboot'
  6. Verify the new kernel is running with 'uname -r' and confirm the version is >= 5.14.8
Caveat Kernel upgrades may require system downtime and could introduce compatibility issues with proprietary kernel modules or older system utilities; ensure backups and test in staging if possible

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

Fix this in Linux Kernel Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
Get it fixed fast

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-0920 — 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-2021-0920 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