CVE-2024-5846: Google Chrome PDFium Use-After-Free Flaw

CVE-2024-5846 Overview

CVE-2024-5846 is a Use After Free vulnerability in PDFium, the PDF rendering engine used by Google Chrome. This memory corruption flaw exists in Chrome versions prior to 126.0.6478.54 and allows a remote attacker to potentially exploit heap corruption via a crafted PDF file. The vulnerability was classified with Medium severity by the Chromium security team.

Critical Impact

Remote attackers can trigger heap corruption through malicious PDF files, potentially leading to arbitrary code execution or browser crashes when users open specially crafted documents.

Affected Products

• Google Chrome (versions prior to 126.0.6478.54)
• Fedora 39 (via Chromium package)
• Fedora 40 (via Chromium package)

Discovery Timeline

• 2024-06-11 - CVE-2024-5846 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-5846

Vulnerability Analysis

This Use After Free (CWE-416) vulnerability resides in PDFium, Chrome's integrated PDF rendering component. Use After Free conditions occur when a program continues to reference memory after it has been freed, creating opportunities for attackers to manipulate the program's execution flow.

In this case, the vulnerability can be triggered when PDFium processes a maliciously crafted PDF document. The flaw allows an attacker to corrupt heap memory, which could potentially be leveraged to execute arbitrary code within the context of the browser process.

The attack requires user interaction—specifically, the victim must open or preview a malicious PDF file. Given Chrome's widespread use as both a browser and PDF viewer, the attack surface is significant. Organizations that handle PDF documents from untrusted sources face elevated risk.

Root Cause

The root cause is a memory management error in PDFium where an object reference is used after the underlying memory has been deallocated. This creates a dangling pointer condition that attackers can exploit by causing the freed memory to be reallocated with attacker-controlled data before the dangling reference is accessed.

Attack Vector

The attack is network-based and requires user interaction. An attacker can deliver the malicious PDF through various channels:

• Email attachments
• Downloads from compromised or malicious websites
• Links shared through messaging platforms
• Drive-by downloads when browsing malicious sites with PDF preview enabled

When a victim opens the crafted PDF file in Google Chrome (either directly or through the built-in PDF viewer), the vulnerability triggers heap corruption that could allow the attacker to execute code within the browser's sandbox context.

Detection Methods for CVE-2024-5846

Indicators of Compromise

• Unexpected Chrome browser crashes when opening PDF files
• Unusual memory consumption patterns in Chrome processes
• Suspicious PDF files with anomalous internal structure or embedded objects
• Chrome renderer process crashes logged in system event logs

Detection Strategies

• Monitor for abnormal Chrome process behavior, particularly renderer crashes when handling PDF content
• Implement endpoint detection rules for suspicious PDF file characteristics and malformed document structures
• Deploy network-based inspection to identify potentially malicious PDF files in transit
• Configure browser telemetry to capture crash reports related to PDFium components

Monitoring Recommendations

• Enable Chrome crash reporting and monitor for PDFium-related crash signatures
• Review endpoint logs for repeated browser crashes correlating with PDF file access
• Implement file integrity monitoring for downloaded PDF documents in high-risk environments
• Monitor network traffic for PDF downloads from suspicious or newly registered domains

How to Mitigate CVE-2024-5846

Immediate Actions Required

• Update Google Chrome to version 126.0.6478.54 or later immediately
• Enable automatic Chrome updates to ensure timely patching of future vulnerabilities
• Advise users to avoid opening PDF files from untrusted or unknown sources
• Consider implementing PDF sanitization or content disarm solutions for email attachments

Patch Information

Google has addressed this vulnerability in Chrome version 126.0.6478.54, released as part of the stable channel update for desktop. Additional technical details can be found in the Chromium Issue Tracker.

For Fedora users, updated packages are available through the standard package management system. See the Fedora package announcements for Fedora 39 and Fedora 40.

Workarounds

• Disable the built-in Chrome PDF viewer and use an alternative PDF reader until patching is complete
• Implement browser policies to block automatic PDF opening in Chrome
• Use browser isolation solutions for untrusted PDF content
• Deploy email gateway policies to quarantine or scan PDF attachments before delivery

# Verify Chrome version is patched (126.0.6478.54 or later)
google-chrome --version

# For Fedora systems, update Chrome/Chromium packages
sudo dnf update chromium

# Optional: Disable Chrome PDF viewer via policy (Linux example)
# Create policy file at /etc/opt/chrome/policies/managed/disable_pdf_viewer.json
echo '{"AlwaysOpenPdfExternally": true}' | sudo tee /etc/opt/chrome/policies/managed/disable_pdf_viewer.json