CVE-2021-34833
📋 TL;DR
CVE-2021-34833 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 code execution in the context of the PDF reader process, allowing attackers to steal documents, install malware, or perform other malicious activities.
If Mitigated
Limited impact if proper application sandboxing, least privilege principles, and network segmentation are implemented.
🎯 Exploit Status
Exploitation requires user interaction but is technically straightforward once the malicious file is opened. The vulnerability was discovered by Zero Day Initiative (ZDI-CAN-14023).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.0.49893 and later versions (specifically fixed in subsequent updates)
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
Restart Required: Yes
Instructions:
1. Download the latest version from Foxit's official website. 2. Run the installer. 3. Follow installation prompts. 4. Restart the system if required. 5. Verify the update by checking Help > About.
🔧 Temporary Workarounds
Disable JavaScript in Foxit Reader
allDisabling JavaScript can prevent exploitation of many PDF vulnerabilities including this one.
Open Foxit Reader > File > Preferences > JavaScript > Uncheck 'Enable JavaScript'
Use Protected View
allEnable Protected View to open PDFs in a restricted mode that prevents code execution.
Open Foxit Reader > File > Preferences > Trust Manager > Check 'Enable Safe Reading Mode'
🧯 If You Can't Patch
- Restrict PDF file handling to alternative PDF readers that are not vulnerable
- Implement application whitelisting to prevent unauthorized code execution
🔍 How to Verify
Check if Vulnerable:
Check Foxit Reader version: Open Foxit Reader > Help > About. If version is 11.0.0.49893 or earlier, the system is vulnerable.Check Version:
On Windows: wmic product where name="Foxit Reader" get versionVerify Fix Applied:
Verify version is 11.0.0.49893 or later after update. Check that JavaScript is disabled if using that workaround.📡 Detection & Monitoring
Log Indicators:
- Unexpected Foxit Reader crashes
- Multiple annotation-related errors in application logs
- Process creation from Foxit Reader with unusual command lines
Network Indicators:
- Downloads of PDF files from suspicious sources
- Outbound connections initiated by Foxit Reader process
SIEM Query:
process_name:"FoxitReader.exe" AND (event_id:1000 OR event_id:1001) OR process_parent_name:"FoxitReader.exe" AND process_name NOT IN ("explorer.exe", "cmd.exe")