CVE-2020-21426
📋 TL;DR
A buffer overflow vulnerability in FreeImage's EXR plugin allows remote attackers to execute arbitrary code by providing a crafted image file. This affects systems using FreeImage 3.18.0 to process EXR image files. Attackers can exploit this without authentication to potentially gain control of affected systems.
💻 Affected Systems
- FreeImage
📦 What is this software?
Freeimage by Freeimage Project
⚠️ 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) or limited code execution within the application context.
If Mitigated
Application crash with no further impact if proper sandboxing or privilege separation is implemented.
🎯 Exploit Status
Exploitation requires crafting a malicious EXR file and getting it processed by vulnerable FreeImage. No public exploit code is known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FreeImage 3.18.0 with patch or later versions
Vendor Advisory: https://sourceforge.net/p/freeimage/bugs/300/
Restart Required: Yes
Instructions:
1. Check current FreeImage version. 2. Update to patched version from official FreeImage repository. 3. Rebuild/redeploy applications using FreeImage. 4. Restart affected services.
🔧 Temporary Workarounds
Disable EXR plugin
allRemove or disable FreeImage's EXR plugin to prevent processing of EXR files
# On Linux: Remove libFreeImage.so symlinks or plugin files related to EXR
# Reconfigure applications to not use EXR format
Input validation
allImplement strict file type validation before passing to FreeImage
# Example: Validate file magic bytes before processing
if (!file_is_safe_exr(file)) { reject_file(); }
🧯 If You Can't Patch
- Implement network segmentation to isolate systems using FreeImage
- Use application sandboxing or containerization to limit exploit impact
🔍 How to Verify
Check if Vulnerable:
Check if FreeImage 3.18.0 is installed and if EXR file processing is enabled in applications.Check Version:
# Linux: dpkg -l | grep freeimage OR rpm -qa | grep -i freeimage
# Or check FreeImage.h header version in source codeVerify Fix Applied:
Verify FreeImage version is updated and test with known safe EXR files to ensure functionality.📡 Detection & Monitoring
Log Indicators:
- Application crashes when processing EXR files
- Unusual process spawning from image processing services
Network Indicators:
- Unexpected outbound connections from image processing systems
- Large EXR file uploads to web applications
SIEM Query:
source="application.log" AND ("FreeImage" OR "EXR") AND ("crash" OR "segfault" OR "buffer overflow")🔗 References
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RUEK2JOVJBQZVNQIIZZO3JFMTVB4R5KS/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UGOMCRAANNCQYJYPPMGRQWKRZGIP6NME/
- https://sourceforge.net/p/freeimage/bugs/300/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RUEK2JOVJBQZVNQIIZZO3JFMTVB4R5KS/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UGOMCRAANNCQYJYPPMGRQWKRZGIP6NME/
- https://sourceforge.net/p/freeimage/bugs/300/
