CVE-2021-34837
📋 TL;DR
CVE-2021-34837 is a use-after-free vulnerability in Foxit PDF Reader that allows remote attackers to execute arbitrary code 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 data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious code execution in the context of the current user, enabling data exfiltration, credential theft, or installation of additional malware.
If Mitigated
Limited impact with proper sandboxing and privilege restrictions, potentially only affecting the PDF Reader process without system-wide compromise.
🎯 Exploit Status
Exploit requires user interaction but has been publicly disclosed through ZDI. Attack vectors include malicious PDF attachments and web pages.
🛠️ 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 application after update.
🔧 Temporary Workarounds
Disable JavaScript in PDF Reader
allPrevents JavaScript-based exploitation vectors
In Foxit Reader: File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
windowsOpen PDFs in sandboxed protected mode
In Foxit Reader: File > Preferences > General > Check 'Open in Protected View'
🧯 If You Can't Patch
- Use alternative PDF readers that are not vulnerable
- Block PDF files from untrusted sources at network perimeter
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Help > About Foxit Reader. If version is 11.0.0.49893 or earlier, system is vulnerable.Check Version:
On Windows: wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 11.0.0.49894 or later in Help > About Foxit Reader.📡 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 to suspicious domains
- PDF downloads from untrusted sources
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR event_id:1001) AND exception_code:0xc0000005