CVE-2021-39686

What it actually does

Race condition in multiple binder.c functions allows incorrect SELinux security domain to be presented, bypassing mandatory access controls to enable local privilege escalation.

Why it matters to the business

Local attackers could obtain elevated system privileges on affected Android devices, risking full device compromise; however low EPSS, lack of KEV listing, and age since 2022 publication indicate limited real-world exploitation urgency.

How an attack unfolds

An attacker with local access on an Android device triggers the race condition in binder.c to supply a misrepresented domain to SELinux, resulting in unauthorized permission grants and privilege escalation without user interaction.

How to fix it

Apply the upstream kernel fix referenced by Android ID A-200688826 via the latest Android security patch level; upgrade to a patched kernel version in subsequent Android releases.

How to confirm the fix worked

Confirm the device is running a kernel build that includes the binder.c race-condition mitigation for A-200688826 by inspecting kernel version strings or security patch level.

Typical attack path

1. Obtain local shell or app execution on target Android device
2. Trigger concurrent binder operations to win the race condition
3. Cause SELinux to evaluate the incorrect security domain
4. Abuse resulting permission bypass for privilege escalation

How to detect it

Review kernel logs for anomalous binder transaction patterns or unexpected SELinux domain transitions around the time of suspected local activity; correlate with process execution of untrusted apps.

What your security team should do

• Prioritize deployment of current Android security updates across managed devices
• Audit local access controls and app permissions to reduce attack surface
• Include binder-related kernel logs in routine security monitoring