CVE-2021-21840
📋 TL;DR
This integer overflow vulnerability in GPAC's MPEG-4 decoder allows heap-based buffer overflow via specially crafted video files. Attackers can achieve remote code execution by tricking users into opening malicious videos. Affects applications using GPAC library for video processing.
💻 Affected Systems
- GPAC Project on Advanced Content library
- Applications using GPAC for MPEG-4 decoding
📦 What is this software?
Gpac by Gpac
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the application processing the video, potentially leading to full system compromise.
Likely Case
Application crash (denial of service) or arbitrary code execution depending on exploit sophistication.
If Mitigated
Application crash without code execution if exploit fails or mitigations like ASLR/DEP are effective.
🎯 Exploit Status
Exploit requires user interaction to open malicious file but no authentication. Public proof-of-concept exists in Talos advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.0.2 or later
Vendor Advisory: https://github.com/gpac/gpac/security/advisories/GHSA-5x5h-9wrq-9hcm
Restart Required: Yes
Instructions:
1. Update GPAC library to v1.0.2 or later. 2. Rebuild applications using GPAC. 3. Restart affected services/applications.
🔧 Temporary Workarounds
Disable MPEG-4 processing
allConfigure applications to disable MPEG-4 file processing if not required.
Application-specific configuration required
Input validation
allImplement file type validation before processing with GPAC library.
Application-specific implementation required
🧯 If You Can't Patch
- Implement strict file upload restrictions and validation for video files
- Use application sandboxing/containerization to limit potential damage
🔍 How to Verify
Check if Vulnerable:
Check GPAC library version: gpac -version or examine linked library version in applications.Check Version:
gpac -version 2>/dev/null | head -1Verify Fix Applied:
Confirm GPAC version is 1.0.2 or higher and applications have been rebuilt with updated library.📡 Detection & Monitoring
Log Indicators:
- Application crashes when processing video files
- Memory access violation errors in application logs
Network Indicators:
- Unusual video file downloads to systems running GPAC applications
SIEM Query:
source="application_logs" AND ("segmentation fault" OR "access violation" OR "heap corruption") AND process="*gpac*"