CVE-2021-34853
📋 TL;DR
CVE-2021-34853 is a use-after-free vulnerability in Foxit PDF Reader that allows remote code execution when users open malicious PDF files or visit malicious web pages. The vulnerability exists in Annotation object handling where the software fails to validate object existence before operations. This affects Foxit PDF Reader users who open untrusted PDF documents.
💻 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 with attacker gaining the same privileges as the PDF Reader process, potentially leading to malware installation, data theft, or lateral movement.
Likely Case
Malware execution on the victim's system, potentially leading to ransomware, credential theft, or system compromise.
If Mitigated
Limited impact if PDF Reader runs with restricted privileges, though user data could still be compromised.
🎯 Exploit Status
Exploitation requires user interaction (opening malicious PDF). The vulnerability was disclosed by ZDI with technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.0.49894 and 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 JavaScript-based exploitation vectors in PDF files
Open Foxit Reader > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed Protected View mode
Open Foxit Reader > File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Restrict Foxit Reader to open only trusted PDFs from known sources
- Run Foxit Reader with minimal user privileges or in application sandbox
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About. 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 11.0.0.49894 or later in Help > About menu.📡 Detection & Monitoring
Log Indicators:
- Foxit Reader crash logs with memory access violations
- Unexpected child processes spawned from Foxit Reader
Network Indicators:
- PDF downloads from suspicious sources followed by unusual outbound connections
SIEM Query:
process_name="FoxitReader.exe" AND (event_id=1000 OR child_process_creation)