CVE-2021-31459
📋 TL;DR
This is a use-after-free vulnerability in Foxit Reader's XFA Forms handling that allows remote code execution. Attackers can exploit it by tricking users into opening malicious PDF files or visiting malicious web pages. Users of Foxit Reader 10.1.1.37576 are affected.
💻 Affected Systems
- Foxit Reader
📦 What is this software?
Phantompdf by Foxitsoftware
Phantompdf by Foxitsoftware
Reader by Foxitsoftware
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining the same privileges as the Foxit Reader process, potentially leading to malware installation, data theft, or lateral movement.
Likely Case
Malware installation on individual workstations, credential theft, or ransomware deployment through malicious PDF documents.
If Mitigated
Limited impact with application sandboxing or restricted user privileges preventing system-wide compromise.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious file). The vulnerability is well-documented with public advisories and likely incorporated into exploit kits.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.1.2 or later
Vendor Advisory: https://www.foxitsoftware.com/support/security-bulletins.php
Restart Required: No
Instructions:
1. Download latest Foxit Reader from official website. 2. Run installer. 3. Follow installation prompts. 4. Verify version is 10.1.2 or higher.
🔧 Temporary Workarounds
Disable XFA Forms
allDisable XFA Forms functionality in Foxit Reader settings to prevent exploitation
Open Foxit Reader > File > Preferences > Trust Manager > Uncheck 'Enable XFA Forms'
Use Alternative PDF Reader
allTemporarily use a different PDF reader that doesn't support XFA Forms
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized PDF readers
- Deploy network filtering to block malicious PDF downloads and restrict internet access for PDF readers
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About Foxit Reader. If version is 10.1.1.37576 or earlier, you are vulnerable.Check Version:
On Windows: wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 10.1.2 or later in Help > About Foxit Reader. Test with known safe XFA forms to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with memory access violations
- Unexpected child processes spawned from Foxit Reader
- Network connections initiated by Foxit Reader process
Network Indicators:
- PDF downloads from suspicious sources followed by Foxit Reader execution
- Outbound connections from Foxit Reader to unknown IPs
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR event_id:1001) AND exception_code:0xc0000005