CVE-2021-33815
📋 TL;DR
This vulnerability in FFmpeg's EXR image decoder allows out-of-bounds array access due to insufficient validation of the dc_count parameter. Attackers can exploit this to potentially execute arbitrary code or cause denial of service by processing specially crafted EXR image files. Systems using FFmpeg 4.4 for media processing are affected.
💻 Affected Systems
- FFmpeg
📦 What is this software?
Ffmpeg by Ffmpeg
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Application crash causing denial of service, potentially disrupting media processing workflows.
If Mitigated
Contained application crash with no privilege escalation if proper sandboxing and least privilege are implemented.
🎯 Exploit Status
Exploitation requires crafting a malicious EXR file, but no public proof-of-concept has been released. The vulnerability is in a widely used library, increasing potential for weaponization.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FFmpeg 4.4.1 and later
Vendor Advisory: https://github.com/FFmpeg/FFmpeg/commit/26d3c81bc5ef2f8c3f09d45eaeacfb4b1139a777
Restart Required: Yes
Instructions:
1. Update FFmpeg to version 4.4.1 or later using your package manager. 2. For Linux: 'sudo apt update && sudo apt upgrade ffmpeg' (Debian/Ubuntu) or 'sudo yum update ffmpeg' (RHEL/CentOS). 3. Restart any services using FFmpeg.
🔧 Temporary Workarounds
Disable EXR decoder
allTemporarily disable FFmpeg's EXR image decoder to prevent exploitation while patching.
ffmpeg -disable-decoder=exr
Input validation
allImplement file type validation to reject EXR files at application level.
🧯 If You Can't Patch
- Implement strict file upload controls and sandbox FFmpeg processes with minimal privileges.
- Deploy network segmentation to isolate media processing systems and monitor for anomalous behavior.
🔍 How to Verify
Check if Vulnerable:
Run 'ffmpeg -version' and check if version is 4.4. Also check if EXR decoder is enabled with 'ffmpeg -decoders | grep exr'.Check Version:
ffmpeg -version | head -1Verify Fix Applied:
After update, confirm version is 4.4.1 or later with 'ffmpeg -version' and test processing a valid EXR file.📡 Detection & Monitoring
Log Indicators:
- FFmpeg segmentation faults or abnormal termination when processing EXR files
- High memory usage or CPU spikes in FFmpeg processes
Network Indicators:
- Unusual EXR file uploads to media processing endpoints
- Outbound connections from FFmpeg processes
SIEM Query:
process.name:ffmpeg AND (event.action:segfault OR event.outcome:failure)