CVE-2021-21838 – This vulnerability allows attackers to execute ... (How to Fix)

Q: What is the severity of CVE-2021-21838?

CVE-2021-21838 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 media processing, potentially compromising user systems through video playback.

📋 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 media processing, potentially compromising user systems through video playback.

💻 Affected Systems

Products:

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

Versions: v1.0.1 and earlier

Operating Systems: Linux, Windows, macOS, Other Unix-like systems

Default Config Vulnerable: ⚠️ Yes

Notes: Any application that uses the vulnerable GPAC library to process MPEG-4 files is affected.

📦 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 code execution in the context of the media player.

🟢

If Mitigated

No impact if patched or if untrusted video files are blocked.

🌐 Internet-Facing: MEDIUM

🏢 Internal Only: LOW

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires user interaction (opening a malicious video file). Proof-of-concept code is available in the Talos advisory.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: v1.0.2 or later

Vendor Advisory: https://github.com/gpac/gpac/issues/1766

Restart Required: Yes

Instructions:

1. Update GPAC library to version 1.0.2 or later.
2. Rebuild or update any applications that link against GPAC.
3. Restart affected applications or services.

🔧 Temporary Workarounds

Block untrusted MPEG-4 files

all

Prevent processing of untrusted MPEG-4 video files at network or application level.

Use application sandboxing

all

Run media players in restricted environments (e.g., containers, sandboxes) to limit impact.

🧯 If You Can't Patch

Disable MPEG-4 decoding in affected applications if possible.
Use alternative media players that don't rely on GPAC library.

🔍 How to Verify

Check if Vulnerable:

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

Check Version:

gpac -version 2>&1 | head -1

Verify Fix Applied:

Confirm GPAC version is 1.0.2 or later and test with known malicious MPEG-4 samples (in safe environment).

📡 Detection & Monitoring

Log Indicators:

Application crashes related to GPAC or media processing
Unexpected process termination of media players

Network Indicators:

Downloads of MPEG-4 files from untrusted sources

SIEM Query:

Process: (gpac OR media_player) AND Event: Crash

📊 Metadata

CVE ID: CVE-2021-21838

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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