CVE-2021-21900
📋 TL;DR
This CVE describes a use-after-free vulnerability in LibreCAD's libdxfrw library that allows remote code execution. Attackers can exploit it by tricking users into opening malicious .dxf files, potentially compromising systems running vulnerable versions. This affects anyone using LibreCAD or software incorporating the vulnerable libdxfrw library.
💻 Affected Systems
- LibreCAD
- libdxfrw
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Libdxfrw by Librecad
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control of the affected system, potentially leading to data theft, ransomware deployment, or lateral movement within networks.
Likely Case
Local privilege escalation or arbitrary code execution in the context of the user opening the malicious file, leading to data compromise and potential persistence.
If Mitigated
Limited impact if proper file validation and user privilege restrictions are in place, potentially resulting in application crash only.
🎯 Exploit Status
Exploitation requires user interaction to open malicious file. The vulnerability is in file parsing code, making reliable exploitation feasible.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: libdxfrw versions after 2.2.0-rc2-19-ge02f3580
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2021/12/msg00002.html
Restart Required: No
Instructions:
1. Update LibreCAD to latest version. 2. For Linux distributions, use package manager: 'sudo apt update && sudo apt upgrade librecad' (Debian/Ubuntu) or 'sudo yum update librecad' (RHEL/CentOS). 3. For Windows/macOS, download latest version from official LibreCAD website.
🔧 Temporary Workarounds
Restrict DXF file processing
allBlock or sandbox processing of untrusted DXF files
User privilege reduction
allRun LibreCAD with limited user privileges to reduce impact
🧯 If You Can't Patch
- Implement strict file validation for DXF files before opening
- Use application whitelisting to prevent unauthorized execution
🔍 How to Verify
Check if Vulnerable:
Check libdxfrw version: 'ldconfig -p | grep libdxfrw' or check LibreCAD version in About dialogCheck Version:
librecad --version or check About in GUIVerify Fix Applied:
Verify updated version is installed and test with known malicious DXF file in sandbox📡 Detection & Monitoring
Log Indicators:
- Application crashes when processing DXF files
- Unusual process creation from LibreCAD
Network Indicators:
- Downloads of DXF files from untrusted sources
SIEM Query:
Process creation where parent process contains 'librecad' or 'dxf' and child process is suspicious🔗 References
- https://lists.debian.org/debian-lts-announce/2021/12/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RDI3HCTCACMIC7I4ILB3NRU6DCMADI5H/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZTIAMP7QJDKV4ADDLR4GVVX2TXYLHVOZ/
- https://security.gentoo.org/glsa/202305-26
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1351
- https://www.debian.org/security/2022/dsa-5077
- https://lists.debian.org/debian-lts-announce/2021/12/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RDI3HCTCACMIC7I4ILB3NRU6DCMADI5H/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZTIAMP7QJDKV4ADDLR4GVVX2TXYLHVOZ/
- https://security.gentoo.org/glsa/202305-26
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1351
- https://www.debian.org/security/2022/dsa-5077
