CVE-2021-21856 – This vulnerability allows remote code execution... (How to Fix)

Q: What is the severity of CVE-2021-21856?

CVE-2021-21856 has a CVSS score of 8.8 (HIGH). This vulnerability allows remote code execution through integer overflow in GPAC's MPEG-4 decoder. Attackers can exploit it by tricking users into opening malicious video files, potentially compromising systems running vulnerable GPAC library versions. Affects applications using GPAC v1.0.1 for media processing.

📋 TL;DR

This vulnerability allows remote code execution through integer overflow in GPAC's MPEG-4 decoder. Attackers can exploit it by tricking users into opening malicious video files, potentially compromising systems running vulnerable GPAC library versions. Affects applications using GPAC v1.0.1 for media processing.

💻 Affected Systems

Products:

GPAC Project on Advanced Content library

Versions: v1.0.1

Operating Systems: All platforms running GPAC

Default Config Vulnerable: ⚠️ Yes

Notes: Any application using GPAC library for MPEG-4 decoding is vulnerable by default.

📦 What is this software?

Gpac by Gpac

View all CVEs affecting Gpac →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Full system compromise with arbitrary code execution leading to data theft, ransomware deployment, or persistent backdoor installation.

🟠

Likely Case

Application crash (denial of service) or limited code execution within the application context.

🟢

If Mitigated

Application crash with no code execution if memory protections (ASLR, DEP) are effective.

🌐 Internet-Facing: MEDIUM

🏢 Internal Only: LOW

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires user interaction (opening malicious file) but no authentication. Proof-of-concept available in Talos advisory.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: v1.0.1+ (patched versions)

Vendor Advisory: https://github.com/gpac/gpac/security/advisories

Restart Required: Yes

Instructions:

1. Update GPAC library to latest version. 2. Rebuild applications using GPAC. 3. Restart affected services.

🔧 Temporary Workarounds

Disable MPEG-4 processing

all

Configure applications to disable MPEG-4 decoding via GPAC

Application-specific configuration required

🧯 If You Can't Patch

Implement application whitelisting to prevent unauthorized executables
Use network segmentation to isolate media processing systems

🔍 How to Verify

Check if Vulnerable:

Check GPAC library version: gpac -version

Check Version:

gpac -version 2>&1 | head -1

Verify Fix Applied:

Verify version is newer than v1.0.1 and check for CVE-2021-21856 in changelog

📡 Detection & Monitoring

Log Indicators:

Application crashes with memory access violations
Unexpected process termination

Network Indicators:

Unusual outbound connections from media processing systems

SIEM Query:

Process:Name='gpac' AND EventID=1000 (Application Crash)

📊 Metadata

CVE ID: CVE-2021-21856

CVSS v3 Score: 8.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-680

Published: August 18, 2021

Last Updated: November 21, 2024

🔗 References

https://talosintelligence.com/vulnerability_reports/TALOS-2021-1299 Exploit,Technical Description,Third Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1299 Exploit,Technical Description,Third Party Advisory

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🔗 Related Vulnerabilities

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