CVE-2021-21843 – This vulnerability allows attackers to execute ... (How to Fix)

Q: What is the severity of CVE-2021-21843?

CVE-2021-21843 has a CVSS score of 8.8 (HIGH). This vulnerability allows attackers to execute arbitrary code or cause denial of service by tricking users into opening specially crafted MPEG-4 video files. It affects applications using the GPAC library for video processing, particularly on 32-bit platforms. Media players, video editors, and web applications that process MPEG-4 content are potentially vulnerable.

📋 TL;DR

This vulnerability allows attackers to execute arbitrary code or cause denial of service by tricking users into opening specially crafted MPEG-4 video files. It affects applications using the GPAC library for video processing, particularly on 32-bit platforms. Media players, video editors, and web applications that process MPEG-4 content are potentially vulnerable.

💻 Affected Systems

Products:

GPAC Project on Advanced Content library
Applications using GPAC library for MPEG-4 decoding

Versions: v1.0.1 and possibly earlier versions

Operating Systems: All platforms (primarily affects 32-bit systems)

Default Config Vulnerable: ⚠️ Yes

Notes: Most severe on 32-bit platforms due to integer overflow characteristics

📦 What is this software?

⚠️ 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 memory corruption leading to unstable behavior.

🟢

If Mitigated

Application crash with no privilege escalation if sandboxed or running with minimal permissions.

🌐 Internet-Facing: MEDIUM

🏢 Internal Only: LOW

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploit requires user interaction to open malicious video file

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: v1.0.1+ (patched versions available)

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

Restart Required: Yes

Instructions:

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

🔧 Temporary Workarounds

Disable MPEG-4 processing

all

Configure applications to disable MPEG-4 video decoding if not required

Application-specific configuration required

Sandbox video processing

linux

Run video processing in isolated containers or sandboxes

docker run --security-opt no-new-privileges ...
firejail --private ...

🧯 If You Can't Patch

Implement strict file upload validation for video files
Use application allowlisting to prevent unauthorized video players

🔍 How to Verify

Check if Vulnerable:

Check GPAC library version: gpac -version or examine linked library versions in applications

Check Version:

gpac -version 2>/dev/null || strings /usr/lib/libgpac.so | grep 'GPAC'

Verify Fix Applied:

Verify GPAC version is newer than v1.0.1 and check for security patches in changelog

📡 Detection & Monitoring

Log Indicators:

Application crashes with memory corruption errors
Segmentation faults in video processing components

Network Indicators:

Unusual MPEG-4 file uploads to web applications
Video file downloads from suspicious sources

SIEM Query:

process_name:"video_player" AND (event_type:"crash" OR memory_violation:"heap")

📊 Metadata

CVE ID: CVE-2021-21843

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-2021-1297 Exploit,Technical Description,Third Party Advisory
https://www.debian.org/security/2021/dsa-4966 Third Party Advisory
https://www.talosintelligence.com/vulnerability_reports/TALOS-2021-1297 Exploit,Technical Description,Third Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1297 Exploit,Technical Description,Third Party Advisory
https://www.debian.org/security/2021/dsa-4966 Third Party Advisory
https://www.talosintelligence.com/vulnerability_reports/TALOS-2021-1297 Exploit,Technical Description,Third Party Advisory

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🔗 Related Vulnerabilities

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