CVE-2021-39793
Google Pixel Out-of-Bounds Write Vulnerability
Description
CVE-2021-39793 is an out-of-bounds write vulnerability in the display driver of Google Pixel devices that allows a local attacker to execute arbitrary code with elevated privileges. The vulnerability resides in the kernel-level display driver, where improper bounds checking during certain display operations can lead to memory corruption. CISA has added CVE-2021-39793 to the Known Exploited Vulnerabilities catalog, confirming targeted exploitation against Pixel devices. With an EPSS score of 0.00151 (55.2nd percentile), this vulnerability has been exploited in limited, targeted attacks rather than widespread campaigns.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| android | - |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
References
- https://source.android.com/security/bulletin/pixel/2022-03-01(Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-39793(Third Party Advisory, US Government Resource)
Weakness Type
CWE-787: Out-of-bounds Write
CWE-787 describes a weakness where software writes data past the end, or before the beginning, of an intended buffer, leading to memory corruption. In CVE-2021-39793, the Google Pixel display driver writes data outside the bounds of an allocated buffer during specific display operations, corrupting kernel memory and enabling privilege escalation from user-space to kernel-level execution.
Learn more: CWE-787 — Out-of-bounds Write
Impact Analysis
CVE-2021-39793 enables local privilege escalation on Google Pixel devices through a kernel-level memory corruption in the display driver. Successful exploitation grants the attacker kernel-level code execution, completely bypassing Android's application sandbox and security model. With kernel access, an attacker can read all data on the device including encrypted credentials, install persistent rootkits that survive factory resets, intercept all communications, and disable security features. While the attack requires local access or a companion application-level vulnerability, it is the critical final step in mobile exploit chains used for surveillance and targeted attacks.
Exploit Maturity
CVE-2021-39793 is listed in the CISA Known Exploited Vulnerabilities catalog, indicating targeted exploitation against Google Pixel devices. The EPSS score of 0.00151 (55.2nd percentile) reflects limited but confirmed exploitation, consistent with targeted mobile attacks rather than mass campaigns. Mobile kernel vulnerabilities are typically exploited by sophisticated threat actors including commercial spyware vendors and nation-state groups, where the targets are high-value individuals such as journalists, activists, and government officials.
Remediation
- Apply Google Pixel security updates immediately as required by CISA KEV: install the latest Android security patch level that addresses the display driver vulnerability.
- Enable automatic security updates on all Google Pixel devices to ensure timely patch deployment.
- For managed Pixel fleets, use mobile device management (MDM) to verify patch compliance and quarantine devices running outdated firmware.
- Review device logs for indicators of exploitation, including unexpected display driver crashes, kernel panics, or application behavior consistent with privilege escalation.
- For high-risk users, consider enabling Android's advanced protection features and restricting installation of applications to the official Google Play Store.
Technical Details
CVE-2021-39793 is an out-of-bounds write vulnerability in the kernel-level display driver specific to Google Pixel devices. The vulnerability occurs when the display driver processes certain display-related operations without proper bounds validation, allowing a write operation to exceed the allocated buffer boundary in kernel memory. The memory corruption can be leveraged to overwrite adjacent kernel data structures, enabling the attacker to manipulate kernel state and achieve code execution at the highest privilege level. As a kernel driver vulnerability, exploitation provides direct access to the kernel address space, bypassing all user-space security mechanisms including SELinux and the Android application sandbox.
Frequently Asked Questions
Is CVE-2021-39793 being actively exploited?
Yes. CVE-2021-39793 is listed in the CISA KEV catalog with confirmed targeted exploitation. Mobile kernel vulnerabilities like this are typically used in sophisticated, targeted attacks against high-value individuals.
What products are affected by CVE-2021-39793?
CVE-2021-39793 specifically affects Google Pixel devices running firmware with the vulnerable display driver. Other Android devices using different display drivers are not affected.
How do I fix CVE-2021-39793?
Install the latest Google Pixel security update. Enable automatic updates to receive security patches promptly.
How severe is CVE-2021-39793?
CVE-2021-39793 is a high-severity kernel privilege escalation vulnerability that enables complete device compromise on Google Pixel devices. While exploitation is targeted rather than widespread, it is a critical component of mobile surveillance attack chains.
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