CVE-2021-39525
📋 TL;DR
CVE-2021-39525 is a heap-based buffer overflow vulnerability in libredwg's bit_read_fixed() function. This allows attackers to execute arbitrary code or cause denial of service by processing specially crafted DWG files. Users and applications that utilize libredwg for DWG file processing are affected.
💻 Affected Systems
- LibreDWG
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Application crash (denial of service) when processing malicious DWG files, potentially disrupting workflows.
If Mitigated
Limited impact if application runs with minimal privileges and proper sandboxing/isolation.
🎯 Exploit Status
Proof-of-concept available in GitHub issue. Exploitation requires user/application to process malicious DWG file.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v0.10.1.3752 and later
Vendor Advisory: https://github.com/LibreDWG/libredwg/issues/261
Restart Required: Yes
Instructions:
1. Update libredwg to version 0.10.1.3752 or later. 2. Rebuild/reinstall any applications using libredwg. 3. Restart affected services/applications.
🔧 Temporary Workarounds
Disable DWG file processing
allTemporarily disable DWG file processing in applications using libredwg.
Sandbox libredwg usage
linuxRun applications using libredwg in isolated containers or with minimal privileges.
docker run --read-only --cap-drop=ALL your_application
🧯 If You Can't Patch
- Implement strict file upload validation to reject suspicious DWG files.
- Deploy application allowlisting to prevent unauthorized code execution.
🔍 How to Verify
Check if Vulnerable:
Check libredwg version: 'dwgread --version' or 'strings /path/to/libredwg.so | grep version'Check Version:
dwgread --version 2>/dev/null || strings $(ldconfig -p | grep libredwg | head -1 | awk '{print $4}') 2>/dev/null | grep -i versionVerify Fix Applied:
Confirm version is 0.10.1.3752 or later using version check command.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults when processing DWG files
- Unusual memory allocation patterns in libredwg processes
Network Indicators:
- Unexpected DWG file downloads/uploads to/from untrusted sources
SIEM Query:
source="application_logs" AND ("segmentation fault" OR "buffer overflow") AND process="*libredwg*"