CVE-2021-37993
📋 TL;DR
This is a use-after-free vulnerability in Google Chrome's PDF accessibility features that allows remote attackers to potentially exploit heap corruption. Attackers can trigger this vulnerability by tricking users into visiting a malicious HTML page, potentially leading to arbitrary code execution. All users running Google Chrome versions prior to 95.0.4638.54 are affected.
💻 Affected Systems
- Google Chrome
📦 What is this software?
Chrome by Google
Google Chrome is the world's most popular web browser, used by over 3 billion users globally across Windows, macOS, Linux, Android, and iOS platforms. As a Chromium-based browser developed by Google, Chrome dominates the browser market with approximately 65% market share, making it a critical compon...
Learn more about Chrome →⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the same privileges as the Chrome process, potentially leading to full system compromise, data theft, or ransomware deployment.
Likely Case
Browser crash (denial of service) or limited memory corruption that could be leveraged for information disclosure or sandbox escape.
If Mitigated
No impact if Chrome is fully patched or if users avoid untrusted websites and PDFs.
🎯 Exploit Status
Use-after-free vulnerabilities typically require some exploitation expertise but are commonly weaponized in browser attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 95.0.4638.54 and later
Vendor Advisory: https://chromereleases.googleblog.com/2021/10/stable-channel-update-for-desktop_19.html
Restart Required: Yes
Instructions:
1. Open Chrome. 2. Click the three-dot menu → Help → About Google Chrome. 3. Chrome will automatically check for updates and install version 95.0.4638.54 or later. 4. Click 'Relaunch' to restart Chrome with the update.
🔧 Temporary Workarounds
Disable PDF accessibility features
allTurn off accessibility features for PDFs to potentially mitigate the vulnerability
chrome://settings/accessibility → Disable 'PDF accessibility' options
Use alternative PDF viewer
allConfigure Chrome to use external PDF viewers instead of built-in PDFium
chrome://settings/content/pdfDocuments → Toggle 'Download PDF files instead of automatically opening them in Chrome'
🧯 If You Can't Patch
- Restrict users from browsing untrusted websites using web filtering or proxy policies
- Implement application whitelisting to prevent execution of malicious payloads that might result from exploitation
🔍 How to Verify
Check if Vulnerable:
Check Chrome version: if it's below 95.0.4638.54, the system is vulnerable.Check Version:
On Windows: "chrome://version/" in address bar. On Linux/macOS: google-chrome --versionVerify Fix Applied:
Confirm Chrome version is 95.0.4638.54 or higher after update.📡 Detection & Monitoring
Log Indicators:
- Chrome crash reports with memory corruption signatures
- Unexpected Chrome process termination
- Accessibility-related error messages in Chrome logs
Network Indicators:
- Requests to known malicious domains hosting exploit pages
- Unusual PDF file downloads followed by Chrome crashes
SIEM Query:
source="chrome_logs" AND ("crash" OR "memory corruption" OR "accessibility") AND version<"95.0.4638.54"🔗 References
- https://chromereleases.googleblog.com/2021/10/stable-channel-update-for-desktop_19.html
- https://crbug.com/1255332
- https://www.debian.org/security/2022/dsa-5046
- https://chromereleases.googleblog.com/2021/10/stable-channel-update-for-desktop_19.html
- https://crbug.com/1255332
- https://www.debian.org/security/2022/dsa-5046
