CVE-2021-31453
📋 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, potentially compromising their systems. Affects Foxit Reader users who open untrusted 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
Full system compromise with attacker gaining same privileges as the user running Foxit Reader, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malware installation on individual workstations, credential theft, or data exfiltration from the compromised system.
If Mitigated
Limited impact with application sandboxing or restricted user privileges, potentially only application crash or denial of service.
🎯 Exploit Status
Exploit requires user to open malicious PDF file. ZDI published details and proof-of-concept is available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Foxit Reader 10.1.2 or later
Vendor Advisory: https://www.foxitsoftware.com/support/security-bulletins.php
Restart Required: Yes
Instructions:
1. Download latest Foxit Reader from official website. 2. Uninstall current version. 3. Install updated version. 4. Restart system.
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
allPrevents XFA forms from executing JavaScript which may mitigate some exploitation vectors
Open Foxit Reader > File > Preferences > Trust Manager > Uncheck 'Enable JavaScript'
Use Protected View
allOpen all PDFs in protected mode to limit potential damage
Open Foxit Reader > File > Preferences > Trust Manager > Check 'Safe Reading Mode'
🧯 If You Can't Patch
- Restrict PDF opening to trusted sources only using application whitelisting
- Run Foxit Reader with limited user privileges or in sandboxed environment
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Help > About Foxit Reader. 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 or later in Help > About Foxit Reader. Test with known safe PDF containing XFA forms.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with memory access violations
- Unexpected child processes spawned from Foxit Reader
Network Indicators:
- Outbound connections from Foxit Reader process 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) AND memory_access_violation