CVE-2021-30551: Google Chrome V8 RCE Vulnerability

CVE-2021-30551 Overview

CVE-2021-30551 is a type confusion vulnerability in the V8 JavaScript engine used by Google Chrome. This vulnerability exists in Chrome versions prior to 91.0.4472.101 and allows a remote attacker to potentially exploit heap corruption via a crafted HTML page. The vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

Critical Impact

This vulnerability enables remote code execution through heap corruption when a user visits a malicious webpage, potentially allowing attackers to execute arbitrary code within the browser's sandbox or escape it entirely.

Affected Products

• Google Chrome versions prior to 91.0.4472.101
• Fedora 33 (via bundled Chromium)
• Fedora 34 (via bundled Chromium)

Discovery Timeline

• June 15, 2021 - CVE-2021-30551 published to NVD
• October 24, 2025 - Last updated in NVD database

Technical Details for CVE-2021-30551

Vulnerability Analysis

This type confusion vulnerability resides in V8, Google Chrome's high-performance JavaScript and WebAssembly engine. Type confusion occurs when a program allocates or initializes a resource (such as a pointer, object, or variable) using one type but later accesses that resource using an incompatible type. In the context of V8, this can lead to memory corruption when the engine incorrectly handles JavaScript objects during execution.

The vulnerability allows attackers to corrupt heap memory by tricking the V8 engine into misinterpreting object types during JavaScript execution. When successfully exploited, this can lead to arbitrary read/write primitives that attackers can leverage for code execution within the renderer process.

Root Cause

The root cause is a type confusion flaw in V8's handling of JavaScript objects. When the JavaScript engine incorrectly tracks or validates object types during optimization passes or runtime execution, it may treat an object of one type as if it were another. This type mismatch leads to memory access violations where the engine reads or writes memory based on incorrect type assumptions, resulting in heap corruption that can be weaponized for arbitrary code execution.

Attack Vector

The attack is network-based and requires user interaction. An attacker must craft a malicious HTML page containing JavaScript code specifically designed to trigger the type confusion in V8. When a victim navigates to the attacker-controlled page using a vulnerable version of Chrome, the malicious JavaScript executes in the browser context.

The exploitation flow typically involves:

1. The victim visits a malicious or compromised website
2. The page loads JavaScript that triggers the type confusion bug in V8
3. The attacker leverages the resulting heap corruption to gain arbitrary read/write capabilities
4. These primitives are used to achieve code execution within the Chrome renderer process
5. Additional exploits may be chained to escape the browser sandbox

This vulnerability was exploited in the wild prior to the patch release, making it a zero-day vulnerability at the time of discovery.

Detection Methods for CVE-2021-30551

Indicators of Compromise

• Unusual Chrome renderer process crashes or memory corruption errors
• JavaScript execution anomalies in browser logs
• Network connections to known malicious domains hosting exploit kits
• Unexpected child process spawning from Chrome renderer processes
• Memory access violations in Chrome crash dumps referencing V8 components

Detection Strategies

• Monitor for Chrome versions below 91.0.4472.101 across the enterprise
• Implement browser version compliance checks as part of endpoint security policies
• Deploy network detection rules for known exploitation patterns targeting V8 vulnerabilities
• Enable Chrome's built-in crash reporting to identify potential exploitation attempts
• Utilize endpoint detection and response (EDR) solutions to monitor for suspicious browser behavior

Monitoring Recommendations

• Configure centralized logging for browser crash reports and correlate with threat intelligence
• Monitor web proxy logs for connections to URLs associated with exploit kit infrastructure
• Implement behavioral analysis for unusual Chrome process activity patterns
• Track software inventory to identify unpatched Chrome installations
• Review CISA KEV alerts and cross-reference with organizational asset inventory

How to Mitigate CVE-2021-30551

Immediate Actions Required

• Update Google Chrome to version 91.0.4472.101 or later immediately
• Enable automatic updates for Chrome to ensure timely security patch deployment
• Verify Chrome update status across all managed endpoints in the organization
• Implement web filtering to block access to known malicious domains
• Consider temporary network-level restrictions if immediate patching is not possible

Patch Information

Google released a security update addressing this vulnerability on June 9, 2021. The fix is included in Chrome version 91.0.4472.101 and all subsequent releases. Organizations should reference the Chrome Stable Channel Update for official patch details.

For Fedora users, security updates are available through the standard package management system. Refer to the Fedora Package Announcement for distribution-specific guidance.

Additional security advisories have been issued by Gentoo GLSA 2021-06 and Gentoo GLSA 2022-08.

Workarounds

• Disable JavaScript execution in Chrome if patching is not immediately possible (significantly impacts functionality)
• Use alternative browsers temporarily while awaiting patch deployment
• Implement network-level controls to restrict access to untrusted websites
• Deploy browser isolation solutions to contain potential exploitation
• Enable Site Isolation in Chrome to limit the impact of renderer process compromises

# Verify Chrome version on Linux/macOS
google-chrome --version

# Force Chrome update check (Windows)
# Navigate to chrome://settings/help in the browser

# Check Chrome version via registry (Windows PowerShell)
Get-ItemProperty -Path "HKLM:\SOFTWARE\Google\Chrome\BLBeacon" -Name "version"