CVE-2021-34841
📋 TL;DR
CVE-2021-34841 is a use-after-free vulnerability in Foxit PDF Reader that allows remote attackers to execute arbitrary code when users open malicious PDF files or visit malicious web pages. This affects Foxit PDF Reader users running vulnerable versions, requiring user interaction to trigger the exploit.
💻 Affected Systems
- Foxit PDF Reader
📦 What is this software?
Pdf Editor by Foxitsoftware
Pdf Editor by Foxitsoftware
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining the same privileges as the PDF Reader process, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malware installation or data exfiltration through malicious PDF documents delivered via phishing or compromised websites.
If Mitigated
Limited impact with proper application sandboxing and least privilege principles, potentially contained to PDF Reader process only.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file). The vulnerability was discovered by Zero Day Initiative (ZDI-CAN-14022).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.1 or later
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
Restart Required: Yes
Instructions:
1. Open Foxit PDF Reader. 2. Go to Help > Check for Updates. 3. Follow prompts to install version 11.0.1 or later. 4. Restart the application.
🔧 Temporary Workarounds
Disable JavaScript in PDF Reader
allPrevents JavaScript-based exploitation vectors in PDF files
In Foxit Reader: File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed protected view mode
In Foxit Reader: File > Preferences > Trust Manager > Enable 'Safe Reading Mode'
🧯 If You Can't Patch
- Replace Foxit PDF Reader with alternative PDF viewers that are not affected
- Implement application whitelisting to block execution of Foxit Reader
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About Foxit Reader. If version is 11.0.0.49893 or earlier, system is vulnerable.Check Version:
On Windows: wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 11.0.1 or later in Help > About Foxit Reader. Test with known safe PDF files to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Multiple crash reports from Foxit Reader process
- Unexpected process creation from Foxit Reader
Network Indicators:
- Outbound connections from Foxit Reader to unknown IPs
- DNS requests for suspicious domains after PDF opening
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR event_id:1001) OR process_parent_name:"FoxitReader.exe" AND process_name NOT IN ("explorer.exe", "svchost.exe")