dbcve.org
AndroidOperating system · Google

CVE-2021-0955

HIGH · 7.0 CVSS v3.1 Published 2021-12-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
72/100
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 pf_write_buf of FuseDaemon.cpp, there is possible memory corruption due to a race condition. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-11Android ID: A-192085766

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

Race condition in FuseDaemon.cpp's pf_write_buf function causes memory corruption, allowing local privilege escalation without additional execution privileges on Android-11 devices.

MitigationApply Android security patch level 2021-11 or later; no configuration-based workarounds exist for this kernel-level race condition vulnerability.

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:= 11.0

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

CVSS:3.1/AV:L/AC:H/PR:L/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 Android version
    Run 'getprop ro.build.version.release' or check Settings > About Phone > Android version
    Affected if Version is exactly 11.0 (the '=' notation indicates exact version matching)
  2. Check security patch level
    Run 'getprop ro.build.version.security_patch' to retrieve the installed patch level
    Affected if Patch level is earlier than 2021-11 (vulnerable if shows 2021-10 or earlier)
  3. Confirm FuseDaemon is in use
    Check if /fuse or /storage/emulated/0 is accessible through FUSE by examining running processes with 'ps -A | grep fuse' or checking /proc/mounts for fuse entries
    Affected if FuseDaemon is actively handling filesystem operations (default on Android 11, but must be running for the race condition to be triggerable)
  4. Verify kernel version
    Run 'uname -r' or check /proc/version to confirm kernel-level exposure
    Affected if Running a kernel shipped with Android 11 base (the vulnerability exists in the FuseDaemon pf_write_buf implementation in that kernel)
  5. Check SELinux context of FuseDaemon
    Run 'ls -la /system/bin/vold' or check FuseDaemon binary permissions; the flaw is in vold's handling of FUSE operations
    Affected if The vold process (which manages FuseDaemon) is running with elevated privileges, which is required for the privilege escalation to be exploitable

Affected if running exactly Android 11.0 with security patch level earlier than November 2021, as later patches contain the fix for the FuseDaemon pf_write_buf race condition.

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 Android security patch level 2021-11 or later; no configuration-based workarounds exist for this kernel-level race condition vulnerability.

Recommended fix Moderate confidence

December 2021 Android Security Patch Level (or later) for Android 11; or Android 12+

  1. Apply the December 2021 Android Security Patch Level (SPL) or later to your Android 11.0 device. This can typically be done through Settings > System > Security Update on supported devices, or by contacting your device manufacturer/OEM for the update.
  2. Verify the update was applied by checking Settings > About Phone > Android version - it should show the December 2021 security patch level or later.
  3. If your device OEM has not released an update containing this fix, consider upgrading to Android 12 if your device is supported, or to a device that receives regular security updates.
Caveat Monthly security patches are cumulative; applying this patch should not introduce breaking changes. However, if upgrading from Android 11 to Android 12, review Android 12 compatibility changes.

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

Fix this in Android Scoped from the published advisory
  • Consultation4.0 h
  • Testing8.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,360
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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-2021-0955 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
  • 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