CVE-2021-34831
📋 TL;DR
CVE-2021-34831 is a use-after-free vulnerability in Foxit Reader that allows remote attackers to execute arbitrary code when users open malicious PDF files or visit malicious web pages. The vulnerability exists due to improper validation of Document objects before performing operations. This affects users of Foxit Reader 10.1.4.37651 and potentially other versions.
💻 Affected Systems
- Foxit 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 within the network.
Likely Case
Local privilege escalation or arbitrary code execution within the context of the Foxit Reader process, enabling malware installation or credential harvesting.
If Mitigated
Limited impact with application sandboxing or restricted user privileges preventing system-wide compromise.
🎯 Exploit Status
Exploit requires user interaction but has been publicly disclosed through ZDI. Weaponization is likely given the RCE nature and PDF reader target.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.1.4.37652 and later
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
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 latest version from Foxit website and install.
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
allPrevents exploitation via malicious JavaScript in PDF files
Open Foxit Reader > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
allOpen PDFs in restricted mode to limit potential damage
Open Foxit Reader > File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized executables from running
- Restrict user privileges to standard user accounts (not administrator)
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About Foxit Reader. If version is 10.1.4.37651 or earlier, system is vulnerable.Check Version:
On Windows: wmic product where name='Foxit Reader' get versionVerify Fix Applied:
Verify version is 10.1.4.37652 or later using same method. Test opening known safe PDF files to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with memory access violations
- Unexpected child processes spawned from Foxit Reader
- Unusual network connections from Foxit Reader process
Network Indicators:
- Outbound connections from Foxit Reader to unknown IPs
- DNS requests for suspicious domains from user workstations
SIEM Query:
process_name='FoxitReader.exe' AND (event_id=1000 OR event_id=1001) AND faulting_module LIKE '%kernel32%'