dbcve.org
AndroidOperating system · Google

CVE-2021-39621

HIGH · 7.8 CVSS v3.1 Published 2022-01-14
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
80/100
Remediation priority · High
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 sendLegacyVoicemailNotification of LegacyModeSmsHandler.java, there is a possible permissions bypass due to an unsafe PendingIntent. This could lead to local escalation of privilege with User execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-10 Android-11 Android-12 Android-9Android ID: A-185126319

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

This is a local privilege escalation vulnerability in Android's LegacyModeSmsHandler component. The issue is an unsafe PendingIntent in the sendLegacyVoicemailNotification method, which lacks proper security flags (likely FLAG_IMMUTABLE) and/or explicit package specification. This allows a malicious local application to intercept or hijack the PendingIntent and execute code with the elevated privileges of the vulnerable SMS/voicemail handling component.

MitigationApply the appropriate security fix in LegacyModeSmsHandler.java by ensuring PendingIntent uses FLAG_IMMUTABLE (or equivalent) and includes explicit package specifications to prevent hijacking. Users should apply the latest Android security patch level from their device OEM.

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:= 9.0= 10.0= 11.0= 12.0

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

CVSS:3.1/AV:L/AC:L/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
    Go to Settings > About Phone > Android version, or run 'getprop ro.build.version.release' via ADB shell
    Affected if Version equals 9.0, 10.0, 11.0, or 12.0
  2. Verify security patch level
    Go to Settings > About Phone > Security patch level, or run 'getprop ro.build.version.security_patch' via ADB shell
    Affected if Patch level is earlier than December 2021 (the fix was released in the December 2021 security update)
  3. Confirm LegacyModeSmsHandler component exists
    Check for the presence of LegacyModeSmsHandler in the system framework by examining /system/framework/services.jar or searching logs for 'LegacyModeSmsHandler' during SMS/voicemail operations
    Affected if The LegacyModeSmsHandler component is present and loaded by the system

A device is affected if it runs Android version 9.0, 10.0, 11.0, or 12.0 with a security patch level before December 2021 and has the LegacyModeSmsHandler component present in the system.

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 appropriate security fix in LegacyModeSmsHandler.java by ensuring PendingIntent uses FLAG_IMMUTABLE (or equivalent) and includes explicit package specifications to prevent hijacking. Users should apply the latest Android security patch level from their device OEM.

Recommended fix High confidence

Android Security Patch Level 2021-12-01 or later for Android 9, 10, 11, and 12

  1. 1. Check your device's current Android security patch level by going to Settings > About Phone > Android version or Settings > Security > Security update
  2. 2. Verify the security patch level is lower than December 2021 (2021-12-01)
  3. 3. Navigate to Settings > System > Software Update (or Settings > About Phone > Software Update)
  4. 4. Check for and install any available system updates
  5. 5. Confirm the security patch level has been updated to 2021-12-01 or later after the update completes
Caveat Standard Android monthly security update with no expected breaking changes; updates are backward-compatible

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

Fix this in Android Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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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-2021-39621 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