CVE-2020-21840
📋 TL;DR
CVE-2020-21840 is a heap-based buffer overflow vulnerability in GNU LibreDWG's bit_search_sentinel function that allows attackers to execute arbitrary code or cause denial of service. This affects users and applications that process malicious DWG files using vulnerable versions of LibreDWG. The vulnerability is triggered when parsing specially crafted DWG files.
💻 Affected Systems
- GNU LibreDWG
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the LibreDWG process, potentially leading to full system compromise.
Likely Case
Application crash (denial of service) when processing malicious DWG files.
If Mitigated
Limited impact if the application runs with minimal privileges and proper sandboxing/isolation.
🎯 Exploit Status
Exploitation requires the victim to process a malicious DWG file. Proof-of-concept code is available in the GitHub issue.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 0.11 and later
Vendor Advisory: https://github.com/LibreDWG/libredwg/issues/188
Restart Required: Yes
Instructions:
1. Download LibreDWG version 0.11 or later from the official repository. 2. Compile and install the new version. 3. Restart any services or applications using LibreDWG.
🔧 Temporary Workarounds
Input Validation
allImplement strict validation of DWG files before processing with LibreDWG.
Sandbox Execution
linuxRun LibreDWG in a sandboxed environment with limited privileges.
firejail --net=none --private /path/to/libredwg
🧯 If You Can't Patch
- Disable LibreDWG processing of untrusted DWG files
- Implement network segmentation to isolate systems using LibreDWG
🔍 How to Verify
Check if Vulnerable:
Check if LibreDWG version is 0.10 or earlier: 'libredwg --version' or check package manager.Check Version:
libredwg --versionVerify Fix Applied:
Verify installation of version 0.11 or later: 'libredwg --version' should show 0.11+.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults when processing DWG files
- Unexpected process termination of LibreDWG
Network Indicators:
- Unusual outbound connections from LibreDWG processes
SIEM Query:
process_name:"libredwg" AND (event_type:"crash" OR exit_code:139)