CVE-2020-21818
📋 TL;DR
A heap-based buffer overflow vulnerability in GNU LibreDWG allows attackers to execute arbitrary code or cause denial of service by processing specially crafted DWG files. This affects systems running vulnerable versions of LibreDWG that process untrusted DWG files. The vulnerability is in the htmlescape function in escape.c.
💻 Affected Systems
- GNU 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 proper input validation and memory protections are in place, though crashes may still occur.
🎯 Exploit Status
Proof-of-concept exists in GitHub issue #182. Exploitation requires crafting a malicious DWG file, which could be automated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 0.10.2642 or later
Vendor Advisory: https://github.com/LibreDWG/libredwg/issues/182
Restart Required: No
Instructions:
1. Check current LibreDWG version. 2. Update to version 0.10.2642 or later via package manager or source compilation. 3. Recompile any applications using LibreDWG.
🔧 Temporary Workarounds
Disable DWG file processing
allPrevent LibreDWG from processing untrusted DWG files by disabling relevant features or using alternative software.
Use memory protection mechanisms
linuxEnable ASLR, DEP, and other memory protection features to reduce exploit success.
echo 2 > /proc/sys/kernel/randomize_va_space
sysctl -w kernel.randomize_va_space=2
🧯 If You Can't Patch
- Implement strict input validation for DWG files, rejecting malformed or suspicious files.
- Isolate LibreDWG processes using sandboxing or containerization to limit potential damage.
🔍 How to Verify
Check if Vulnerable:
Check LibreDWG version: 'dwgread --version' or 'libredwg --version'. If version is 0.10.2641 or earlier, it is vulnerable.Check Version:
dwgread --version 2>/dev/null || libredwg --version 2>/dev/null || echo 'LibreDWG not found'Verify Fix Applied:
After update, verify version is 0.10.2642 or later using the same command. Test with known safe DWG files to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Application crashes or segmentation faults in LibreDWG processes
- Unusual memory usage patterns in process logs
Network Indicators:
- Unexpected file transfers of DWG files to vulnerable systems
- Network scans targeting LibreDWG services
SIEM Query:
process_name:"dwgread" OR process_name:"libredwg" AND (event_type:"crash" OR memory_usage > threshold)