CVE-2021-39801

What it actually does

Use-after-free condition in ion_ioctl due to improper locking allows a local process to reference freed kernel memory and corrupt kernel structures.

Why it matters to the business

Attackers with a foothold on an Android device can obtain root-level control, bypassing all OS protections and accessing every app and data store.

How an attack unfolds

A local attacker invokes the ION ioctl interface with crafted arguments that trigger a race between allocation and release paths; the missing lock permits reuse of a dangling pointer, enabling kernel memory overwrite and privilege escalation to root.

How to fix it

Apply the upstream kernel commit that adds proper locking around ION buffer operations; rebuild and deploy the patched kernel to all affected Android devices; verify the fix is present in the running kernel image.

How to confirm the fix worked

Confirm the patched kernel source contains the locking change around ion_ioctl; run device-specific regression tests that exercise ION allocation paths; monitor kernel logs for use-after-free warnings after update.

Typical attack path

1. Obtain a local shell or app context on the target Android device
2. Open /dev/ion and issue ioctl calls that race allocation and free operations
3. Trigger the use-after-free to corrupt kernel data structures
4. Escalate to root privileges and install persistent malware or exfiltrate data

How to detect it

Review kernel audit logs and dmesg for repeated ION ioctl failures or warnings; correlate with sudden root-level process creation from unprivileged UIDs; inspect for unexpected modifications to kernel memory mappings.

What your security team should do

• Prioritize deployment of the corrected Android kernel to all managed devices within the next patch cycle
• Restrict untrusted applications from direct ION access via SELinux policy where possible
• Monitor vendor security bulletins for the specific kernel version that resolves A-209791720