CVE-2021-39793

What is Google Pixel?

Google Pixel devices are Android smartphones and tablets developed directly by Google, running the Android operating system with Pixel-exclusive hardware, drivers, and firmware components. Because Pixel devices include hardware components (GPU, camera, modem) with proprietary kernel drivers developed by Google or component manufacturers, Pixel devices receive separate security bulletins covering Pixel-specific vulnerabilities that are distinct from the general Android Security Bulletin. Local privilege escalation vulnerabilities in Pixel are typically used as the second stage of a two-step exploit chain: a browser or app vulnerability provides initial code execution, then a kernel privilege escalation is used to escape the sandbox and achieve full device access.

Overview

CVE-2021-39793 is an out-of-bounds write vulnerability (CWE-787) in a Google Pixel device component — likely a kernel driver for Pixel-specific hardware such as the GPU, camera, or display subsystem. A logic error in the driver allows a low-privileged application to write data beyond the intended memory bounds, leading to local privilege escalation. An attacker with limited code execution (e.g., from a malicious app or browser sandbox escape) can exploit this vulnerability to gain full kernel-level access to the device. Google patched this in the March 2022 Pixel Update Bulletin. CISA added it to KEV in April 2022, reflecting confirmed exploitation in the wild — most likely as part of a targeted spyware or commercial surveillance tool chain.

Affected Versions

Technical Details

The vulnerability is in a Pixel-specific kernel component:

• Root cause: Out-of-bounds write (CWE-787) — a logic error in a device driver processes data in a way that allows memory writes beyond the intended buffer boundary, corrupting adjacent kernel memory structures
• Privilege requirements: Requires low-privileged code execution — an unprivileged app with normal Android permissions (AV:L, PR:L) can trigger the vulnerability
• No user interaction needed — the exploit is triggered programmatically from a malicious application
• Impact: Successful exploitation grants kernel-level access on the Pixel device, bypassing the Android sandbox, app permissions model, and SELinux enforcement
• Exploitation context: Kernel privilege escalation bugs like this are almost exclusively used as the second stage in a chained exploit for device compromise — paired with an initial code execution bug (browser, messaging, or app vulnerability) to achieve full persistent access

Discovery

Details kept minimal per Google's standard practice for actively exploited vulnerabilities. The combination of CISA KEV classification and the Pixel-specific nature suggests exploitation by commercial spyware operators (who focus on Pixel as a high-value espionage target) or nation-state actors.

Exploitation Context

Google Pixel privilege escalation bugs are high-value to commercial surveillance tool vendors and nation-state mobile espionage operators. These bugs are typically chained with browser zero-days or app vulnerabilities to achieve full device compromise for spyware installation. The relatively small window between the March 2022 patch and the April 2022 CISA KEV addition suggests active exploitation around the time of the patch.

Remediation

1. Apply the March 2022 Google Pixel security update (2022-03-05 patch level or later)
2. Enable automatic security updates on Pixel devices to receive patches as soon as they are available
3. If targeted surveillance is suspected: use Google's built-in Android safety features, or consult Amnesty International's MVT (Mobile Verification Toolkit) for forensic analysis
4. Organizations with government or executive personnel at elevated spyware risk should enforce minimum Android security patch level policies via MDM