CVE-2021-34849
📋 TL;DR
CVE-2021-34849 is a use-after-free vulnerability in Foxit PDF Reader that allows remote attackers to execute arbitrary code. Attackers can exploit this by tricking users into opening malicious PDF files or visiting malicious web pages. This affects users running vulnerable versions of Foxit PDF Reader.
💻 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 arbitrary code execution with the privileges of the current user, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious actors deliver malware payloads through phishing emails with malicious PDF attachments, compromising individual workstations.
If Mitigated
If proper application whitelisting and least privilege principles are implemented, exploitation would be limited to the user's context with restricted impact.
🎯 Exploit Status
Exploitation requires user interaction but is straightforward once malicious content is delivered. The vulnerability was discovered by Zero Day Initiative (ZDI-CAN-14531).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.0.49943 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 Reader
windowsPrevents exploitation through malicious JavaScript in PDF files
Open Foxit Reader > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in protected mode to limit potential damage
Open Foxit Reader > File > Preferences > General > Check 'Open documents in Protected Mode'
🧯 If You Can't Patch
- Replace Foxit PDF Reader with alternative PDF viewer that is not vulnerable
- Implement application control to block execution of Foxit Reader entirely
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About Foxit Reader. If version is 11.0.0.49893 or earlier, system is vulnerable.Check Version:
wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 11.0.0.49943 or later in Help > About Foxit Reader.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with exception codes
- Unexpected child processes spawned from Foxit Reader
- Network connections from Foxit Reader process to suspicious IPs
Network Indicators:
- HTTP requests from Foxit Reader to unusual domains
- DNS queries for known exploit kit domains
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR parent_process_name:"FoxitReader.exe")