CVE-2021-31455
📋 TL;DR
This is a use-after-free vulnerability in Foxit Reader's XFA form handling that allows remote code execution when users open malicious PDF files. Attackers can exploit this to execute arbitrary code with the same privileges as the current user. Affects Foxit Reader users who open untrusted PDF documents.
💻 Affected Systems
- Foxit Reader
📦 What is this software?
Foxit Reader by Foxitsoftware
Phantompdf by Foxitsoftware
Phantompdf by Foxitsoftware
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via arbitrary code execution with user privileges, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malware installation or data exfiltration when users open weaponized PDF documents from phishing emails or malicious websites.
If Mitigated
Limited impact if application is sandboxed or runs with minimal privileges, though code execution within the process context still occurs.
🎯 Exploit Status
Exploitation requires user to open malicious PDF but is straightforward once triggered. ZDI published technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.1.2.37615 and later
Vendor Advisory: https://www.foxitsoftware.com/support/security-bulletins.php
Restart Required: No
Instructions:
1. Open Foxit Reader. 2. Go to Help > Check for Updates. 3. Follow prompts to install latest version. 4. Alternatively, download and install latest version from Foxit website.
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
allPrevents JavaScript-based exploitation vectors in PDF files
File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
allOpens PDFs in sandboxed mode with reduced privileges
File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Use alternative PDF readers that are not vulnerable
- Block PDF files from untrusted sources at email/web gateways
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version in Help > About. If version is 10.1.1.37576 or earlier, system is vulnerable.Check Version:
On Windows: wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 10.1.2.37615 or later in Help > About.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with exception codes
- Process creation from foxitreader.exe with unusual parameters
Network Indicators:
- Outbound connections from Foxit Reader process to suspicious IPs
- DNS requests for known C2 domains after PDF opening
SIEM Query:
process_name:foxitreader.exe AND (event_id:1000 OR parent_process:cmd.exe OR parent_process:powershell.exe)