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AndroidOperating system · Google

CVE-2021-39736

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 prepare_io_entry and prepare_response of lwis_ioctl.c and lwis_periodic_io.c, there is a possible out of bounds write due to an integer overflow. 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-205995773References: 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 · high confidence

A kernel driver vulnerability in Android's lwis_ioctl.c and lwis_periodic_io.c contains an integer overflow in the prepare_io_entry and prepare_response functions. This overflow allows an out-of-bounds write, enabling a local attacker with System privileges to escalate to elevated privileges. No user interaction is required.

MitigationApply the vendor-provided kernel patch which adds proper bounds validation to prevent integer overflow in the size calculations before memory allocation and writes.

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 version
    Run 'adb shell getprop ro.build.version.release' or check Settings > About Phone > Android version
    Affected if Any version (the CVE states all Android versions are affected before the patch)
  2. Check security patch level
    Run 'adb shell getprop ro.build.version.security_patch' to see the installed patch month/year (e.g., 2022-01, 2022-02)
    Affected if Patch level is earlier than the month the CVE fix was released in the Android Security Bulletin (CVE-2021-39736 was fixed in the January 2022 Android Security Bulletin)
  3. Verify kernel version
    Run 'adb shell uname -r' or 'adb shell cat /proc/version' to identify the kernel version
    Affected if Kernel version is older than the patched kernel version for your Android release
  4. Confirm lwis driver presence
    Check if the lwis driver is loaded or present by running 'adb shell ls /dev/lwis*' or 'adb shell grep -i lwis /proc/modules' (if module is loaded)
    Affected if The lwis driver is present and loaded on the device - this driver contains the vulnerable code paths (prepare_io_entry and prepare_response functions in lwis_ioctl.c and lwis_periodic_io.c)
  5. Verify System privilege exposure
    Review if any application or service runs with System-level privileges (shell 'ps -A | grep -i system' or check installed apps with UID 1000)
    Affected if Applications or services with System UID (1000) are present - an attacker with System privileges can exploit this vulnerability to escalate to root

A device is likely affected if it runs any Android version without the January 2022 or later security patch, has the lwis driver loaded, and has processes running with System-level privileges that could trigger the integer overflow in prepare_io_entry or prepare_response functions.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-provided kernel patch which adds proper bounds validation to prevent integer overflow in the size calculations before memory allocation and writes.

Fix this in Android Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA3.0 h
17.0 hours of engineering $2,970
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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-2021-39736 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