CVE-2021-30535: Google Chrome Use-After-Free Vulnerability

CVE-2021-30535 Overview

CVE-2021-30535 is a double free vulnerability in the International Components for Unicode (ICU) library used by Google Chrome prior to version 91.0.4472.77. This memory corruption flaw allows a remote attacker to potentially exploit heap corruption via a crafted HTML page, which could lead to arbitrary code execution within the context of the browser.

Critical Impact

Remote attackers can exploit heap corruption through specially crafted web pages, potentially achieving arbitrary code execution with the privileges of the browser process.

Affected Products

• Google Chrome versions prior to 91.0.4472.77
• Fedora 33 (via bundled Chromium packages)
• Fedora 34 (via bundled Chromium packages)

Discovery Timeline

• 2021-06-07 - CVE-2021-30535 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-30535

Vulnerability Analysis

This vulnerability is classified as CWE-415 (Double Free), a critical memory corruption issue that occurs when a program attempts to free the same memory location twice. In the context of Chrome's ICU implementation, this creates a dangerous condition where heap metadata becomes corrupted, potentially allowing an attacker to manipulate memory allocations.

The ICU library is responsible for handling internationalization and Unicode processing in Chrome. When processing certain malformed input, the library can trigger a double free condition in its memory management routines. This type of vulnerability is particularly dangerous in browser contexts because it can be triggered remotely through malicious web content without any user interaction beyond visiting a compromised page.

Root Cause

The root cause of CVE-2021-30535 lies in improper memory lifecycle management within the ICU component of Google Chrome. Double free vulnerabilities occur when code paths incorrectly assume ownership of dynamically allocated memory, leading to the same memory block being released multiple times. This corrupts the heap allocator's internal data structures and can be leveraged by attackers to achieve arbitrary read/write primitives.

Attack Vector

The attack is delivered over the network and requires user interaction in the form of visiting a malicious web page. An attacker would craft a specially designed HTML page that triggers the vulnerable code path in the ICU library. Upon rendering the malicious content, the double free condition is triggered, corrupting heap memory. Through heap manipulation techniques, attackers can potentially:

1. Achieve arbitrary code execution within the browser's renderer process
2. Escape the browser sandbox to gain elevated privileges
3. Compromise the confidentiality, integrity, and availability of the user's system

The vulnerability requires no special privileges and can be exploited with low attack complexity once a victim visits the attacker-controlled page.

Detection Methods for CVE-2021-30535

Indicators of Compromise

• Unexpected Chrome renderer process crashes or restarts during web browsing
• Memory corruption signatures in crash dumps referencing ICU library functions
• Anomalous heap allocation patterns in browser process memory
• Network traffic to suspicious domains hosting crafted HTML payloads

Detection Strategies

• Monitor for Chrome crash reports containing ICU-related stack traces
• Deploy endpoint detection solutions capable of identifying heap spray and heap corruption exploitation techniques
• Implement network-based detection for known malicious HTML patterns targeting browser vulnerabilities
• Use browser telemetry to identify unusual rendering behavior or memory allocation anomalies

Monitoring Recommendations

• Enable Chrome crash reporting and analyze crash dumps for ICU-related memory corruption patterns
• Deploy SentinelOne Singularity to detect and block exploitation attempts at the endpoint level
• Monitor browser version compliance across the enterprise to ensure patched versions are deployed
• Establish alerts for browsers operating below version 91.0.4472.77

How to Mitigate CVE-2021-30535

Immediate Actions Required

• Update Google Chrome to version 91.0.4472.77 or later immediately
• Enable automatic Chrome updates to receive security patches promptly
• For Fedora users, apply available package updates through the package manager
• Consider restricting access to untrusted web content until patches are applied

Patch Information

Google addressed this vulnerability in the Chrome stable channel update released on May 25, 2021. The fix is included in Chrome version 91.0.4472.77 and all subsequent releases. Organizations should verify Chrome versions across their fleet and ensure automatic updates are enabled.

For detailed information about the security update, refer to the Google Chrome Release Blog. The underlying bug is tracked in the Chromium Bug Tracker.

Fedora users should apply available updates from the Fedora Package Announcements for their respective distribution versions.

Workarounds

• Use an alternative browser until Chrome can be updated to a patched version
• Implement web filtering to block access to known malicious sites
• Enable site isolation features in Chrome to limit the impact of renderer exploits
• Consider browser isolation solutions for high-risk browsing activities

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

# Update Chrome on Fedora
sudo dnf update chromium

# Check for available updates on Debian/Ubuntu
apt list --upgradable | grep chromium