CVE-2021-21106: Google Chrome Use After Free Vulnerability

CVE-2021-21106 Overview

CVE-2021-21106 is a critical use-after-free vulnerability in the autofill component of Google Chrome prior to version 87.0.4280.141. This memory corruption flaw allows a remote attacker who has already compromised the renderer process to potentially escape Chrome's sandbox by tricking a user into visiting a specially crafted HTML page. The vulnerability represents a significant security risk as it enables attackers to break out of Chrome's security sandbox, potentially gaining access to the underlying operating system.

Critical Impact

An attacker who has compromised the Chrome renderer process can leverage this vulnerability to escape the browser sandbox and execute arbitrary code with elevated privileges on the victim's system.

Affected Products

• Google Chrome versions prior to 87.0.4280.141
• Fedora 32 and Fedora 33 (via Chromium packages)
• Debian Linux 10.0

Discovery Timeline

• 2021-01-08 - CVE-2021-21106 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-21106

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) exists within Chrome's autofill functionality. Use-after-free vulnerabilities occur when a program continues to use a pointer after the memory it references has been freed. In this case, the autofill component improperly handles memory during certain operations, creating a dangling pointer that can be exploited.

The vulnerability is particularly dangerous because it can be triggered remotely through a crafted HTML page and provides a sandbox escape vector. Chrome's multi-process architecture includes a sandbox to isolate the renderer process from the rest of the system. However, this vulnerability allows an attacker who has already gained code execution within the renderer to break out of this isolation.

The attack requires user interaction (visiting a malicious page) but has a changed scope, meaning successful exploitation can impact resources beyond the vulnerable component's security authority.

Root Cause

The root cause is improper memory management in Chrome's autofill subsystem. When the autofill component processes certain form data, it fails to properly track the lifecycle of memory objects. This leads to a condition where freed memory is subsequently accessed, causing undefined behavior that can be weaponized by attackers. The specific issue was tracked in Chrome Bug Report #1148749.

Attack Vector

The attack vector is network-based and requires the following conditions:

1. The attacker must first compromise Chrome's renderer process through a separate vulnerability or exploit chain
2. The victim must navigate to a malicious webpage crafted by the attacker
3. The crafted HTML page triggers the use-after-free condition in the autofill component
4. Successful exploitation allows the attacker to escape the sandbox and execute code outside the browser's security boundary

The vulnerability leverages the autofill functionality, which processes form data automatically. By carefully crafting the HTML and timing of operations, an attacker can manipulate memory allocation and deallocation to control the freed memory region, potentially redirecting execution flow.

Detection Methods for CVE-2021-21106

Indicators of Compromise

• Unusual Chrome renderer process crashes or restarts, particularly when interacting with web forms
• Unexpected child processes spawned by Chrome with elevated privileges
• Memory corruption artifacts in Chrome crash dumps referencing autofill components
• Network connections to suspicious domains immediately following form interactions

Detection Strategies

• Monitor Chrome version deployments across the enterprise and flag any instances running versions prior to 87.0.4280.141
• Implement endpoint detection rules to identify unusual process hierarchies originating from Chrome processes
• Deploy browser-based telemetry to detect anomalous autofill behavior patterns
• Utilize memory forensics tools to identify use-after-free exploitation attempts in Chrome process memory

Monitoring Recommendations

• Enable Chrome's built-in crash reporting to capture potential exploitation attempts
• Configure SIEM rules to correlate Chrome crashes with subsequent suspicious system activity
• Monitor for unusual network activity from Chrome processes that may indicate post-exploitation communication
• Implement behavioral analytics to detect sandbox escape indicators such as unexpected file system or registry access from browser contexts

How to Mitigate CVE-2021-21106

Immediate Actions Required

• Update Google Chrome to version 87.0.4280.141 or later immediately across all systems
• Verify patch deployment using browser version checks or enterprise management tools
• Review systems for indicators of compromise if running vulnerable versions
• Consider temporarily restricting access to untrusted websites until patching is complete

Patch Information

Google has released a security update addressing this vulnerability in Chrome version 87.0.4280.141. The fix was announced in the Google Chrome Stable Channel Update. Linux distributions have also released corresponding updates:

• Debian users should apply DSA-4832
• Fedora users should apply updates via the Fedora Package Announcement
• Gentoo users should reference GLSA 202101-05

Workarounds

• If immediate patching is not possible, consider disabling Chrome's autofill feature via Group Policy or user settings
• Implement strict web content filtering to block access to potentially malicious sites
• Use network segmentation to limit the impact of potential sandbox escapes
• Consider temporarily using alternative browsers while awaiting patch deployment in high-security environments

# Disable Chrome autofill via command line flag (temporary workaround)
google-chrome --disable-autofill-download-manager

# Verify Chrome version to confirm patch status
google-chrome --version
# Expected output: Google Chrome 87.0.4280.141 or higher