CVE-2021-34843
📋 TL;DR
This vulnerability in Foxit PDF Reader allows remote attackers to execute arbitrary code by tricking users into opening malicious PDF files. The flaw exists in how Annotation objects are handled without proper validation, leading to use-after-free conditions. Users of affected Foxit PDF Reader versions are at risk.
💻 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 current user, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malware installation or data exfiltration from the compromised system, often through phishing campaigns delivering malicious PDFs.
If Mitigated
Limited impact with proper application sandboxing and user privilege restrictions, potentially only affecting the PDF reader process.
🎯 Exploit Status
Exploit requires user to open malicious PDF but is otherwise straightforward. ZDI published advisory with technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.0.49894 and 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 latest version
4. Restart computer after installation
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
windowsPrevents JavaScript-based exploitation vectors in PDF files
Open Foxit Reader > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed Protected View mode
Open Foxit Reader > File > Preferences > General > Check 'Open documents in Protected View'
🧯 If You Can't Patch
- Use alternative PDF reader software temporarily
- Block PDF files from untrusted sources at email/web gateway
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version in Help > About. If version is 11.0.0.49893 or earlier, system is vulnerable.Check Version:
wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 11.0.0.49894 or later in Help > About.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with memory access violations
- Windows Event Logs showing Foxit Reader process termination
Network Indicators:
- PDF downloads from suspicious sources
- Unusual outbound connections after PDF opening
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR event_id:1001) AND memory_access_violation