CVE-2021-26252
📋 TL;DR
CVE-2021-26252 is a heap buffer overflow vulnerability in htmldoc's PDF processing component that could allow attackers to execute arbitrary code or cause denial of service. This affects systems running htmldoc v1.9.12 when processing malicious HTML files. Users who convert HTML to PDF using vulnerable htmldoc versions are at risk.
💻 Affected Systems
- htmldoc
📦 What is this software?
Fedora by Fedoraproject
Htmldoc by Htmldoc Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the htmldoc process, potentially leading to full system compromise.
Likely Case
Application crash causing denial of service, with potential for limited code execution in specific conditions.
If Mitigated
Application crash without code execution if exploit fails or mitigations are in place.
🎯 Exploit Status
Exploit requires crafting a malicious HTML file that triggers the buffer overflow. Public proof-of-concept exists in Red Hat Bugzilla.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.9.13 or later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1967009
Restart Required: No
Instructions:
1. Download htmldoc v1.9.13 or later from official sources. 2. Uninstall current version. 3. Install patched version. 4. Verify installation with 'htmldoc --version'.
🔧 Temporary Workarounds
Disable PDF output
allTemporarily disable PDF generation functionality in htmldoc
# Modify htmldoc configuration to disable PDF output
# Or use alternative output formats like PostScript
Input validation
allImplement strict input validation for HTML files before processing
# Use file validation scripts to check HTML files
# Implement file type verification before passing to htmldoc
🧯 If You Can't Patch
- Restrict htmldoc execution to trusted users only
- Implement network segmentation to isolate systems running vulnerable htmldoc
🔍 How to Verify
Check if Vulnerable:
Run 'htmldoc --version' and check if output shows v1.9.12Check Version:
htmldoc --versionVerify Fix Applied:
Run 'htmldoc --version' and confirm version is v1.9.13 or later📡 Detection & Monitoring
Log Indicators:
- Segmentation fault errors in system logs
- Abnormal process termination of htmldoc
- Large memory allocation failures
Network Indicators:
- Unusual file uploads to systems running htmldoc
- HTTP requests with crafted HTML content
SIEM Query:
process_name:"htmldoc" AND (event_type:"segmentation_fault" OR exit_code:139)