CVE-2021-34960
📋 TL;DR
This is a use-after-free vulnerability in Foxit PDF Editor's handling of Circle Annotation objects, allowing remote attackers to execute arbitrary code when a user opens a malicious PDF file or visits a malicious webpage. It affects users of Foxit PDF Editor who interact with untrusted PDF content, potentially leading to full system compromise.
💻 Affected Systems
- Foxit PDF Editor
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the current user, leading to complete system takeover, data theft, or ransomware deployment.
Likely Case
Malicious actors trick users into opening crafted PDFs, resulting in malware installation or credential harvesting.
If Mitigated
With patching and security controls, risk is reduced to minimal, though user error could still trigger exploitation.
🎯 Exploit Status
Exploitation is straightforward once a malicious PDF is crafted, but requires user interaction to open the file.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.1.0.52543 and later
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
Restart Required: Yes
Instructions:
1. Open Foxit PDF Editor. 2. Go to Help > Check for Updates. 3. Follow prompts to install version 11.1.0.52543 or newer. 4. Restart the application after installation.
🔧 Temporary Workarounds
Disable PDF opening in Foxit Editor
windowsChange default PDF handler to a non-vulnerable application like Adobe Reader or a web browser.
Windows: Control Panel > Default Programs > Set Default Programs, select alternative PDF viewer
Restrict execution of Foxit PDF Editor
windowsUse application control policies to block Foxit PDF Editor from running, especially for untrusted users.
Windows: Use Group Policy or AppLocker to deny Foxit executable
🧯 If You Can't Patch
- Implement strict email filtering to block malicious PDF attachments and educate users on phishing risks.
- Use endpoint detection and response (EDR) tools to monitor for suspicious process execution from Foxit PDF Editor.
🔍 How to Verify
Check if Vulnerable:
Check the Foxit PDF Editor version: open the application, go to Help > About, and verify if version is below 11.1.0.52543.Check Version:
On Windows: wmic product where name="Foxit PDF Editor" get versionVerify Fix Applied:
After updating, confirm the version is 11.1.0.52543 or higher in Help > About.📡 Detection & Monitoring
Log Indicators:
- Unusual process spawns from Foxit PDF Editor, crash logs related to annotation handling
Network Indicators:
- Downloads of PDF files from untrusted sources, followed by Foxit process activity
SIEM Query:
Process creation where parent process contains 'Foxit' and command line includes '.pdf' from suspicious IPs