CVE-2020-21843
📋 TL;DR
CVE-2020-21843 is a heap-based buffer overflow vulnerability in GNU LibreDWG 0.10, allowing attackers to execute arbitrary code or cause denial-of-service by processing malicious DWG files. It affects users of LibreDWG software for handling CAD files, particularly in environments where untrusted files are processed.
💻 Affected Systems
- GNU LibreDWG
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, data theft, or ransomware deployment.
Likely Case
Denial-of-service crashes or limited code execution in sandboxed environments.
If Mitigated
Minimal impact if file processing is restricted to trusted sources or with memory protections enabled.
🎯 Exploit Status
Proof-of-concept details are available in public references; exploitation is straightforward via crafted DWG files.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 0.10; check for updates like 0.11 or later.
Vendor Advisory: https://github.com/LibreDWG/libredwg/issues/188
Restart Required: No
Instructions:
1. Update LibreDWG to the latest version from the official repository. 2. Recompile or reinstall the software. 3. Verify the fix by testing with known malicious files.
🔧 Temporary Workarounds
Restrict file processing
allLimit LibreDWG usage to trusted, validated DWG files only.
Enable memory protections
linuxUse OS-level protections like ASLR and DEP to reduce exploit success.
echo 2 > /proc/sys/kernel/randomize_va_space (Linux for ASLR)
🧯 If You Can't Patch
- Isolate LibreDWG instances in sandboxed environments or virtual machines.
- Implement strict input validation and block untrusted DWG file uploads or processing.
🔍 How to Verify
Check if Vulnerable:
Check if LibreDWG version is 0.10 or earlier; test with a proof-of-concept DWG file if available.Check Version:
libredwg --version or check package manager (e.g., dpkg -l libredwg on Debian).Verify Fix Applied:
Update to a patched version and confirm it no longer crashes or exhibits overflow behavior with test files.📡 Detection & Monitoring
Log Indicators:
- Application crashes, segmentation faults, or abnormal termination logs in syslog or application logs.
Network Indicators:
- Unusual file uploads or downloads of DWG files to/from vulnerable systems.
SIEM Query:
Example: 'event_source="libredwg" AND (event_type="crash" OR event_type="error")'