CVE-2021-40394
📋 TL;DR
CVE-2021-40394 is a critical out-of-bounds write vulnerability in Gerbv's RS-274X aperture macro handling that allows remote code execution via malicious Gerber files. Users who process untrusted Gerber files with vulnerable Gerbv versions are affected. This vulnerability has a CVSS score of 9.8, indicating critical severity.
💻 Affected Systems
- Gerbv
- Forked Gerbv
📦 What is this software?
Gerbv by Gerbv Project
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining complete control over the affected system, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Remote code execution allowing attackers to run arbitrary commands, install malware, or create persistent backdoors on systems processing malicious Gerber files.
If Mitigated
Limited impact with proper segmentation and file validation, potentially only affecting isolated Gerbv processes without system-wide compromise.
🎯 Exploit Status
Exploitation requires the victim to open a malicious Gerber file. The vulnerability is in file parsing, so no authentication is needed. Public PoC exists in Talos advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Gerbv 2.8.0 and later
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2023/09/msg00040.html
Restart Required: Yes
Instructions:
1. Update Gerbv to version 2.8.0 or later. 2. For Debian systems: apt-get update && apt-get upgrade gerbv. 3. Restart any processes using Gerbv.
🔧 Temporary Workarounds
File validation and sandboxing
allImplement strict file validation for Gerber files and run Gerbv in isolated containers or sandboxes
docker run --rm -v $(pwd):/files gerbv:latest /files/input.gbr
Disable RS-274X macro processing
allIf possible, disable RS-274X aperture macro functionality in Gerbv configuration
🧯 If You Can't Patch
- Isolate Gerbv to dedicated systems with no network access
- Implement strict file validation and only process Gerber files from trusted sources
🔍 How to Verify
Check if Vulnerable:
Check Gerbv version: gerbv --version. If version is 2.7.0 or development commit b5f1eacd/71493260, system is vulnerable.Check Version:
gerbv --versionVerify Fix Applied:
Verify Gerbv version is 2.8.0 or later: gerbv --version📡 Detection & Monitoring
Log Indicators:
- Multiple Gerbv process crashes
- Unusual file processing from untrusted sources
- Suspicious child processes spawned from Gerbv
Network Indicators:
- Unexpected outbound connections from Gerbv processes
- Downloads of Gerber files from untrusted sources
SIEM Query:
process_name:"gerbv" AND (process_crash OR child_process_spawn)🔗 References
- https://lists.debian.org/debian-lts-announce/2023/09/msg00040.html
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1404
- https://www.debian.org/security/2022/dsa-5306
- https://lists.debian.org/debian-lts-announce/2023/09/msg00040.html
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1404
- https://www.debian.org/security/2022/dsa-5306
