CVE-2021-39636

What it actually does

The functions do_ipt_get_ctl and do_ipt_set_ctl in ip_tables.c can return uninitialized kernel memory, enabling local disclosure of kernel information when invoked with system execution privileges.

Why it matters to the business

Devices remain exposed to kernel information leaks that could help attackers escalate privileges or develop further exploits, increasing long-term risk on unpatched Android systems.

How an attack unfolds

An attacker with system-level execution rights calls the vulnerable ip_tables control functions to trigger reads of uninitialized kernel memory and extracts the leaked data without requiring user interaction.

How to fix it

Apply the latest Android kernel security updates that properly initialize data in the affected ip_tables functions; monitor Google security bulletins for kernel patches.

How to confirm the fix worked

Verify kernel source changes that zero or initialize relevant structures before returning from do_ipt_get_ctl and do_ipt_set_ctl; confirm devices receive and apply recent Android security patch levels.

Typical attack path

1. Obtain system execution privileges on an Android device
2. Invoke do_ipt_get_ctl or do_ipt_set_ctl with specific parameters
3. Read and parse the returned uninitialized kernel memory contents

How to detect it

Review kernel audit logs and system call traces for repeated or anomalous invocations of ip_tables control operations; correlate with privilege-escalation attempts or unexpected kernel memory reads.

What your security team should do

• Prioritize deployment of Android kernel security updates across the fleet
• Reduce unnecessary system-level privileges granted to applications and services
• Monitor Google Android security bulletins for future kernel fixes