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AndroidOperating system · Google

CVE-2021-39718

MEDIUM · 6.7 CVSS v3.1 Published 2022-03-16
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 ProtocolStkProactiveCommandAdapter::Init of protocolstkadapter.cpp, there is a possible out of bounds write due to an incorrect bounds check. 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-205035540References: N/A

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

This is an out-of-bounds write vulnerability in the ProtocolStkProactiveCommandAdapter::Init function within protocolstkadapter.cpp in the Android kernel. The flaw stems from an incorrect bounds check that fails to properly validate array or buffer indices before writing data, potentially allowing memory corruption. A local attacker with System-level execution privileges could exploit this to escalate privileges further.

MitigationApply the Android kernel security patch for CVE-2021-39718, which corrects the bounds checking logic in protocolstkadapter.cpp. This patch is delivered through Android's monthly security update process.

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. Check Android security patch level
    Go to Settings > About Phone > Android version or run 'getprop ro.build.version.security_patch' via adb shell
    Affected if The patch level is earlier than the month the CVE-2021-39718 fix was released (typically November 2021 or later)
  2. Check kernel version
    Run 'uname -r' or check /proc/version via adb shell
    Affected if The kernel version predates the patched kernel that includes the fix for protocolstkadapter.cpp bounds check
  3. Verify STK adapter module presence
    Check for the presence of protocolstkadapter related kernel modules or grep for 'ProtocolStkProactiveCommandAdapter' in /proc/kallsyms if available
    Affected if The kernel contains the vulnerable ProtocolStkProactiveCommandAdapter::Init function without the bounds check correction
  4. Check Android build fingerprint
    Run 'getprop ro.build.fingerprint' via adb shell to identify the exact Android build
    Affected if The build is an unpatched version that predates the November 2021 Android security update

A system is affected if it runs an Android version with a security patch level before the fix was applied or a kernel version that lacks the corrected bounds checking in protocolstkadapter.cpp for the ProtocolStkProactiveCommandAdapter component.

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 Android kernel security patch for CVE-2021-39718, which corrects the bounds checking logic in protocolstkadapter.cpp. This patch is delivered through Android's monthly security update process.

Recommended fix Moderate confidence

Android security patch level containing fix for A-205035540 (check Android Security Bulletins)

  1. Check the Android Security Bulletin for the month this CVE was fixed (CVE-2021-39718 was addressed in the December 2021 or January 2022 Android Security Bulletin)
  2. Apply the monthly security patch update for your Android device that includes the fix for this vulnerability
  3. Verify the device has the security patch level that includes the fix for A-205035540
Caveat Monthly security patches typically do not introduce breaking changes but may vary by device manufacturer

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

Fix this in Android Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing12.0 h
  • Review / QA5.0 h
26.0 hours of engineering $4,380
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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-2021-39718 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