CVE-2021-21861
📋 TL;DR
CVE-2021-21861 is an integer truncation vulnerability in GPAC's MPEG-4 decoder that allows heap-based buffer overflow via specially crafted video files. Attackers can exploit this by tricking users into opening malicious videos, potentially leading to arbitrary code execution. This affects applications using GPAC library version 1.0.1 for media processing.
💻 Affected Systems
- GPAC Project on Advanced Content library
📦 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 limited memory corruption leading to unstable behavior.
If Mitigated
Application crash without code execution if memory protections (ASLR, DEP) are effective.
🎯 Exploit Status
Exploitation requires user interaction to open malicious video file. Public proof-of-concept exists in Talos advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.0.1+ (patched versions available in downstream distributions)
Vendor Advisory: https://github.com/gpac/gpac/issues/1766
Restart Required: Yes
Instructions:
1. Update GPAC library to patched version from official repository or distribution channels. 2. Rebuild/redeploy applications using GPAC. 3. Restart affected services.
🔧 Temporary Workarounds
Input validation
allImplement strict validation of MPEG-4 file inputs before processing
Sandbox media processing
allIsolate media processing components in restricted environments
🧯 If You Can't Patch
- Block processing of untrusted MPEG-4 files
- Implement application allowlisting to prevent unauthorized media players
🔍 How to Verify
Check if Vulnerable:
Check GPAC library version: gpac -version or examine linked library versions in applicationsCheck Version:
gpac -version 2>/dev/null | head -1Verify Fix Applied:
Verify updated version is installed and applications are rebuilt with patched library📡 Detection & Monitoring
Log Indicators:
- Application crashes with memory access violations
- Unexpected process termination during media processing
Network Indicators:
- Downloads of suspicious video files from untrusted sources
SIEM Query:
Process:Name="*gpac*" OR Process:Name="*media*" AND EventID=1000 OR EventID=1001 (Windows) OR kernel:segfault (Linux)