CVE-2020-15999: Google Chrome Buffer Overflow Vulnerability

CVE-2020-15999 Overview

CVE-2020-15999 is a critical heap buffer overflow vulnerability in the FreeType font rendering library embedded in Google Chrome versions prior to 86.0.4240.111. This vulnerability allows a remote attacker to potentially exploit heap corruption via a crafted HTML page, enabling arbitrary code execution within the context of the browser process. The vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.

Critical Impact

This vulnerability enables remote code execution through maliciously crafted web content. Attackers can achieve heap corruption by exploiting the FreeType library's font parsing functionality, potentially leading to complete system compromise when users visit malicious websites.

Affected Products

• Google Chrome (versions prior to 86.0.4240.111)
• FreeType library
• Debian Linux 10.0
• Fedora 31
• openSUSE Backports SLE 15.0 SP2
• NetApp ONTAP Select Deploy Administration Utility

Discovery Timeline

• 2020-11-03 - CVE-2020-15999 published to NVD
• 2025-10-24 - Last updated in NVD database

Technical Details for CVE-2020-15999

Vulnerability Analysis

This heap buffer overflow vulnerability (CWE-787, CWE-120) exists within the FreeType library's handling of font data. FreeType is a widely-used open-source font engine that provides font rendering capabilities for numerous applications, including web browsers like Google Chrome. The vulnerability is triggered when the library processes specially crafted font files embedded in HTML pages.

The flaw occurs during the parsing of font data structures, where insufficient bounds checking allows an attacker to write data beyond the allocated heap buffer boundaries. This type of memory corruption can lead to arbitrary code execution, as attackers can manipulate heap metadata and control program execution flow.

Root Cause

The root cause of this vulnerability is inadequate bounds validation in FreeType's font parsing routines. When processing certain font data structures, the library fails to properly validate the size of input data against the allocated buffer size. This allows an attacker to craft malicious font data that exceeds the expected boundaries, resulting in a heap buffer overflow condition.

The vulnerability specifically manifests when Chrome renders web pages containing embedded fonts with malformed data structures designed to trigger the overflow condition.

Attack Vector

The attack is network-based and requires user interaction—specifically, a victim must visit a malicious webpage containing the crafted HTML content. The attack flow typically involves:

1. An attacker creates a webpage containing a specially crafted font file designed to trigger the heap buffer overflow
2. The victim visits the malicious webpage through Google Chrome
3. Chrome's rendering engine invokes FreeType to process the embedded font
4. The malformed font data triggers the heap buffer overflow during parsing
5. The attacker exploits the heap corruption to achieve code execution within the browser's sandboxed process

The vulnerability does not require any special privileges and can be exploited through standard web browsing activity, making it particularly dangerous for drive-by download attacks.

Detection Methods for CVE-2020-15999

Indicators of Compromise

• Unusual memory access patterns in browser processes, particularly related to font rendering operations
• Chrome crash dumps indicating heap corruption in FreeType-related functions
• Suspicious web pages containing embedded fonts with abnormal data structures
• Process behavior anomalies following visits to untrusted websites

Detection Strategies

• Monitor for browser process crashes with signatures indicating heap corruption in font rendering subsystems
• Implement network-based detection for HTML pages containing suspicious embedded font data
• Deploy endpoint detection and response (EDR) solutions capable of identifying heap overflow exploitation attempts
• Analyze browser memory dumps for indicators of FreeType library exploitation

Monitoring Recommendations

• Enable Chrome's built-in crash reporting and monitor for patterns indicating exploitation attempts
• Implement web content filtering to block access to known malicious domains
• Deploy browser isolation technologies to contain potential exploitation within sandboxed environments
• Monitor system logs for post-exploitation indicators such as unusual child process creation from browser processes

How to Mitigate CVE-2020-15999

Immediate Actions Required

• Update Google Chrome to version 86.0.4240.111 or later immediately
• Update the FreeType library to the patched version across all affected systems
• Apply security updates from Debian, Fedora, openSUSE, and other affected distributions
• Review and update any applications that embed vulnerable versions of FreeType

Patch Information

Google released Chrome version 86.0.4240.111 on October 20, 2020, which addresses this vulnerability. The fix has been incorporated into the upstream FreeType library and distributed through security updates by various Linux distributions. Organizations should consult the following advisories for distribution-specific patch information:

• Chrome Stable Channel Update
• Debian Security Advisory DSA-4824
• Gentoo GLSA 2020-11-12
• Fedora Package Announcement

Additional technical details are available in the Google Project Zero RCA and the Chromium Bug Report.

Workarounds

• Disable JavaScript in Chrome as a temporary measure to reduce attack surface (Settings > Privacy and security > Site Settings > JavaScript)
• Use browser isolation or sandboxing solutions to contain potential exploitation
• Implement strict content security policies to limit font loading from untrusted sources
• Consider using alternative browsers while awaiting patch deployment in critical environments

# Verify Chrome version is patched
google-chrome --version
# Output should show version 86.0.4240.111 or higher

# Check FreeType library version on Linux systems
pkg-config --modversion freetype2

# Force Chrome update via command line
google-chrome --check-for-update