CVE-2020-24999
📋 TL;DR
CVE-2020-24999 is an invalid memory access vulnerability in Xpdf's fprintf function that can be triggered by processing a malicious PDF file. This allows remote attackers to cause denial of service (segmentation fault) or potentially execute arbitrary code. Users of Xpdf's pdftohtml binary are affected.
💻 Affected Systems
- Xpdf
- pdftohtml
📦 What is this software?
Xpdf by Xpdfreader
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise
Likely Case
Denial of service through application crash
If Mitigated
Application crash with no further impact if properly sandboxed
🎯 Exploit Status
Exploitation requires sending crafted PDF to pdftohtml; public proof-of-concept available
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Xpdf 4.0.3 and later
Vendor Advisory: https://forum.xpdfreader.com/viewtopic.php?f=3&t=42029
Restart Required: No
Instructions:
1. Download Xpdf 4.0.3 or later from https://www.xpdfreader.com/download.html
2. Compile and install following the provided instructions
3. Replace existing pdftohtml binary with the patched version
🔧 Temporary Workarounds
Disable pdftohtml processing
linuxRemove or disable pdftohtml binary to prevent exploitation
sudo rm /usr/bin/pdftohtml
sudo chmod 000 /usr/bin/pdftohtml
Sandbox PDF processing
linuxRun pdftohtml in a container or sandboxed environment
docker run --rm -v $(pwd):/pdfs xpdf pdftohtml input.pdf output.html
🧯 If You Can't Patch
- Implement strict input validation for PDF files before processing
- Monitor for segmentation faults in pdftohtml processes and alert on anomalies
🔍 How to Verify
Check if Vulnerable:
Check Xpdf version: pdftohtml -v 2>&1 | grep versionCheck Version:
pdftohtml -v 2>&1 | grep versionVerify Fix Applied:
Verify version is 4.0.3 or higher: pdftohtml -v 2>&1 | grep -E '4\.0\.([3-9]|[1-9][0-9])'📡 Detection & Monitoring
Log Indicators:
- Segmentation fault errors in system logs
- Unexpected pdftohtml process termination
Network Indicators:
- Unusual PDF file uploads to web applications
- PDF processing from untrusted sources
SIEM Query:
process.name="pdftohtml" AND event.action="segmentation fault"