CVE-2026-6300: Google Chrome CSS Use-After-Free Flaw

CVE-2026-6300 Overview

CVE-2026-6300 is a use after free vulnerability in the CSS engine of Google Chrome prior to version 147.0.7727.101. This memory corruption flaw allows a remote attacker to execute arbitrary code within the browser's sandbox by convincing a user to visit a maliciously crafted HTML page. The vulnerability resides in Chrome's CSS parsing and rendering components, where improper memory management can lead to a dangling pointer condition that attackers can exploit.

Critical Impact

Successful exploitation enables remote code execution within Chrome's sandbox, potentially allowing attackers to compromise user sessions, steal sensitive data, or chain with sandbox escape vulnerabilities for full system compromise.

Affected Products

• Google Chrome prior to version 147.0.7727.101
• Chromium-based browsers using vulnerable CSS engine versions
• Desktop platforms (Windows, macOS, Linux) running affected Chrome versions

Discovery Timeline

• 2026-04-15 - CVE-2026-6300 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2026-6300

Vulnerability Analysis

This use after free vulnerability (CWE-416) occurs in Chrome's CSS processing engine. Use after free conditions arise when a program continues to reference memory after it has been freed, leading to undefined behavior. In the context of browser security, such flaws are particularly dangerous because attackers can manipulate the heap to place controlled data in the freed memory region, then trigger the dangling pointer reference to achieve code execution.

The vulnerability requires user interaction—specifically, the victim must navigate to or be redirected to a malicious webpage containing specially crafted HTML and CSS content. Once triggered, the attacker can execute arbitrary code within Chrome's renderer process sandbox. While the sandbox provides a layer of protection, this vulnerability still poses significant risk as it can be combined with sandbox escape techniques for complete system compromise.

Root Cause

The root cause stems from improper lifecycle management of CSS-related objects within Chrome's rendering engine. When certain CSS constructs are processed, the code path fails to properly track object references, leading to a scenario where memory is freed prematurely while active references still exist. Subsequent operations that attempt to use these stale references trigger the use after free condition. This type of memory safety issue is common in complex C++ codebases like Chromium where manual memory management intersects with intricate object relationships.

Attack Vector

Exploitation occurs via the network attack vector, requiring the attacker to host or inject malicious content that the victim's browser will render. The attack flow typically involves:

1. Attacker creates a webpage with specially crafted CSS that triggers the vulnerable code path
2. Victim is lured to visit the malicious page through phishing, malvertising, or compromised legitimate websites
3. Chrome's CSS engine processes the malicious content, triggering the use after free condition
4. Attacker-controlled data is executed within the renderer process sandbox

The vulnerability mechanism involves crafted CSS constructs that manipulate Chrome's internal object lifecycle. The CSS engine fails to properly validate object state before dereferencing pointers, allowing attackers to exploit the race between object destruction and subsequent access. For detailed technical analysis, see the Chromium Issue Tracker Entry.

Detection Methods for CVE-2026-6300

Indicators of Compromise

• Unusual Chrome renderer process crashes or memory access violations in CSS-related code paths
• Browser process spawning unexpected child processes or exhibiting anomalous behavior after visiting untrusted websites
• Memory dump analysis showing heap corruption patterns consistent with use after free exploitation

Detection Strategies

• Monitor for Chrome crash reports with signatures matching CSS engine memory corruption
• Deploy browser-based exploit detection solutions that can identify heap spray and memory manipulation techniques
• Implement network-level inspection for known exploit patterns in HTML/CSS payloads targeting this vulnerability

Monitoring Recommendations

• Enable Chrome's built-in crash reporting and analyze crash telemetry for patterns indicating exploitation attempts
• Monitor endpoint detection solutions for suspicious behavior originating from Chrome renderer processes
• Track Google's security announcements via the Chrome Releases Blog for updates on exploitation in the wild

How to Mitigate CVE-2026-6300

Immediate Actions Required

• Update Google Chrome to version 147.0.7727.101 or later immediately across all managed endpoints
• Enable automatic updates to ensure timely patching of future Chrome security vulnerabilities
• Restrict access to untrusted websites and implement web filtering to reduce exposure to potential exploit hosting sites

Patch Information

Google has released Chrome version 147.0.7727.101 which addresses this vulnerability. The fix resolves the memory lifecycle management issue in the CSS engine, ensuring proper reference tracking and preventing the use after free condition. Organizations should prioritize deployment of this update across all managed Chrome installations.

For official patch details, refer to the Google Chrome Update Announcement.

Workarounds

• Consider using alternative browsers temporarily if immediate patching is not feasible, though this is not a long-term solution
• Implement strict content security policies to limit CSS sources to trusted origins
• Deploy endpoint protection solutions capable of detecting and blocking memory corruption exploitation techniques

# Verify Chrome version on Linux/macOS
google-chrome --version
# Expected output: Google Chrome 147.0.7727.101 or later

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