CVE-2021-34835
📋 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 when users open malicious PDFs from phishing emails or compromised websites.
If Mitigated
Limited impact with proper application sandboxing, endpoint protection, and user training preventing malicious file execution.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious PDF) but the technical complexity is low. 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 application. 5. Verify version is 11.0.0.49894 or higher.
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
allPrevents JavaScript-based exploitation vectors in PDF files
File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed protected view mode
File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Block PDF files from untrusted sources at email/web gateways
- Use alternative PDF readers that are not vulnerable
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: 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 11.0.0.49894 or higher in Help > About Foxit Reader.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with exception codes
- Unexpected child processes spawned 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 parent_process:"FoxitReader.exe" AND process_creation