CVE-2021-34952
📋 TL;DR
This vulnerability in Foxit PDF Reader allows remote attackers to execute arbitrary code by exploiting a use-after-free flaw in Annotation object handling. It affects users who open malicious PDF files or visit malicious web pages, requiring user interaction to trigger the exploit.
💻 Affected Systems
- Foxit PDF Reader
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining control of the user's system, potentially leading to data theft, ransomware deployment, or lateral movement within a network.
Likely Case
Remote code execution in the context of the current user, enabling malware installation, credential harvesting, or further exploitation of the system.
If Mitigated
Limited impact if patched or with strict controls, such as blocking untrusted PDFs, but residual risk from social engineering or insider threats.
🎯 Exploit Status
Exploitation requires user interaction but is unauthenticated; weaponization is likely due to the nature of RCE vulnerabilities in widely used software.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Foxit PDF Reader version 11.0.1 or later (check vendor advisory for exact version).
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
Restart Required: Yes
Instructions:
1. Visit the Foxit security bulletins page. 2. Download and install the latest version of Foxit PDF Reader. 3. Restart the system to ensure the patch is fully applied.
🔧 Temporary Workarounds
Disable PDF handling in web browsers
allPrevent automatic opening of PDFs in browsers to reduce attack surface.
For Firefox: Set pdfjs.disabled to true in about:config
For Chrome: Disable 'Open PDF files in the default PDF viewer application' in settings
Use alternative PDF readers
allTemporarily switch to a non-vulnerable PDF reader until patched.
🧯 If You Can't Patch
- Implement application whitelisting to block execution of unauthorized PDF readers or related processes.
- Enforce strict email and web filtering to block malicious PDF attachments and links, and educate users on phishing risks.
🔍 How to Verify
Check if Vulnerable:
Check the Foxit PDF Reader version in the application's 'Help' > 'About' menu; if below 11.0.1, it is likely vulnerable.Check Version:
On Windows: Run 'wmic product where name="Foxit PDF Reader" get version' in Command Prompt; on macOS/Linux, check via GUI or package manager.Verify Fix Applied:
After updating, verify the version is 11.0.1 or higher in the 'About' menu and test with known safe PDFs to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from Foxit PDF Reader (e.g., cmd.exe, powershell.exe)
- Crashes or errors in Foxit application logs related to Annotation handling
Network Indicators:
- Outbound connections from Foxit PDF Reader to unknown IPs or domains, especially after opening a PDF
SIEM Query:
Example: Process creation where parent process name contains 'Foxit' and (process name contains 'cmd' or 'powershell')