CVE-2021-30123 – CVE-2021-30123 is a buffer overflow vulnerabili... (How to Fix)

Q: How do I fix CVE-2021-30123?

1. Update FFmpeg to version 4.3.1 or later using your package manager. 2. For Linux: 'sudo apt update && sudo apt upgrade ffmpeg' (Debian/Ubuntu) or 'sudo yum update ffmpeg' (RHEL/CentOS). 3. For Windows/macOS: Download latest version from ffmpeg.org. 4. Restart all services using FFmpeg.

Q: What is the severity of CVE-2021-30123?

CVE-2021-30123 has a CVSS score of 8.8 (HIGH). CVE-2021-30123 is a buffer overflow vulnerability in FFmpeg's libavcodec library that allows remote attackers to execute arbitrary code by providing a specially crafted media file. This affects all systems running FFmpeg version 4.3 or earlier for media processing. Organizations using FFmpeg for video transcoding, streaming, or media processing are at risk.

📋 TL;DR

CVE-2021-30123 is a buffer overflow vulnerability in FFmpeg's libavcodec library that allows remote attackers to execute arbitrary code by providing a specially crafted media file. This affects all systems running FFmpeg version 4.3 or earlier for media processing. Organizations using FFmpeg for video transcoding, streaming, or media processing are at risk.

💻 Affected Systems

Products:

FFmpeg

Versions: All versions <= 4.3

Operating Systems: Linux, Windows, macOS, BSD, All platforms running FFmpeg

Default Config Vulnerable: ⚠️ Yes

Notes: Any application or service using FFmpeg's libavcodec library to process media files is affected. This includes web applications, media servers, and video processing pipelines.

📦 What is this software?

Ffmpeg by Ffmpeg

View all CVEs affecting Ffmpeg →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the FFmpeg process, potentially leading to full system compromise, data theft, or lateral movement within the network.

🟠

Likely Case

Application crash (denial of service) or limited code execution depending on exploit sophistication and system hardening.

🟢

If Mitigated

Application crash with no code execution if memory protections (ASLR, DEP) are effective and process runs with limited privileges.

🌐 Internet-Facing: HIGH - FFmpeg often processes user-uploaded media files from untrusted sources, making internet-facing instances prime targets.

🏢 Internal Only: MEDIUM - Internal systems processing media from controlled sources have lower risk, but still vulnerable to insider threats or compromised files.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires crafting a malicious media file, but public proof-of-concept exists. Weaponization is likely given the RCE potential and widespread FFmpeg usage.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: FFmpeg 4.3.1 and later

Vendor Advisory: https://trac.ffmpeg.org/ticket/8845

Restart Required: Yes

Instructions:

1. Update FFmpeg to version 4.3.1 or later using your package manager. 2. For Linux: 'sudo apt update && sudo apt upgrade ffmpeg' (Debian/Ubuntu) or 'sudo yum update ffmpeg' (RHEL/CentOS). 3. For Windows/macOS: Download latest version from ffmpeg.org. 4. Restart all services using FFmpeg.

🔧 Temporary Workarounds

Input Validation and Sandboxing

all

Implement strict input validation for media files and run FFmpeg in a sandboxed/containerized environment with minimal privileges.

docker run --read-only --cap-drop=ALL --security-opt=no-new-privileges -v /input:/input:ro ffmpeg-container

Network Segmentation

all

Isolate FFmpeg processing systems from critical network segments and implement egress filtering.

🧯 If You Can't Patch

Implement strict file type validation and only accept media files from trusted sources.
Run FFmpeg processes with minimal privileges (non-root user) and in isolated containers with resource limits.

🔍 How to Verify

Check if Vulnerable:

Check FFmpeg version: 'ffmpeg -version | head -1'. If version is 4.3 or earlier, system is vulnerable.

Check Version:

ffmpeg -version | head -1

Verify Fix Applied:

After update, run 'ffmpeg -version | head -1' and confirm version is 4.3.1 or later.

📡 Detection & Monitoring

Log Indicators:

FFmpeg process crashes with segmentation faults
Unusual child process spawning from FFmpeg
Abnormal memory usage patterns in FFmpeg processes

Network Indicators:

Unexpected outbound connections from media processing systems
Large or malformed media file uploads to FFmpeg endpoints

SIEM Query:

process_name:ffmpeg AND (event_id:1000 OR exit_code:0xC0000005) OR process_parent_name:ffmpeg AND process_name:(cmd.exe OR powershell.exe OR sh OR bash)

📊 Metadata

CVE ID: CVE-2021-30123

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-120

Published: April 7, 2021

Last Updated: November 21, 2024

🔗 References

http://git.videolan.org/?p=ffmpeg.git%3Ba=commitdiff%3Bh=d6f293353c94c7ce200f6e0975ae3de49787f91f
https://security.gentoo.org/glsa/202105-24 Third Party Advisory
https://trac.ffmpeg.org/ticket/8845 Exploit,Vendor Advisory
https://trac.ffmpeg.org/ticket/8863 Exploit,Vendor Advisory
http://git.videolan.org/?p=ffmpeg.git%3Ba=commitdiff%3Bh=d6f293353c94c7ce200f6e0975ae3de49787f91f
https://security.gentoo.org/glsa/202105-24 Third Party Advisory
https://trac.ffmpeg.org/ticket/8845 Exploit,Vendor Advisory
https://trac.ffmpeg.org/ticket/8863 Exploit,Vendor Advisory

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🔗 Related Vulnerabilities

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