CVE-2021-34839
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on affected Foxit PDF Reader installations by tricking users into opening malicious PDF files. The flaw exists in how Annotation objects are handled, allowing attackers to perform operations on non-existent objects. Users of vulnerable Foxit PDF Reader versions are affected.
💻 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 through remote code execution with user privileges, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious PDF files delivered via email or web downloads execute code to steal credentials, install malware, or establish persistence.
If Mitigated
Limited impact with proper application sandboxing, least privilege, and network segmentation preventing lateral movement.
🎯 Exploit Status
Exploitation requires user interaction but is straightforward once malicious PDF is opened. ZDI advisory suggests weaponization is likely.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.1.49911 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 latest version. 4. Restart computer after installation.
🔧 Temporary Workarounds
Disable JavaScript in Foxit
windowsPrevents JavaScript-based exploitation vectors
Open Foxit > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed mode
Open Foxit > File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Block PDF files at email gateways and web proxies
- Use application whitelisting to prevent Foxit execution
🔍 How to Verify
Check if Vulnerable:
Check Foxit version in Help > About. If version is 11.0.0.49893 or earlier, system is vulnerable.Check Version:
Not applicable for GUI application. Use Help > About menu.Verify Fix Applied:
Verify version is 11.0.1.49911 or later in Help > About.📡 Detection & Monitoring
Log Indicators:
- Foxit crash logs with memory access violations
- Unexpected child processes spawned from Foxit
Network Indicators:
- Foxit process making unexpected outbound connections after PDF open
SIEM Query:
Process creation where parent_process contains 'FoxitReader.exe' and command_line contains unusual parameters