CVE-2021-25804 – A NULL-pointer dereference vulnerability in VLC... (How to Fix)

Q: What is the severity of CVE-2021-25804?

CVE-2021-25804 has a CVSS score of 7.5 (HIGH). A NULL-pointer dereference vulnerability in VLC Media Player's AVI file handling can cause the application to crash when opening a specially crafted AVI file. This affects VLC 3.0.11 users who open untrusted media files. The vulnerability results in denial of service but does not allow arbitrary code execution.

📋 TL;DR

A NULL-pointer dereference vulnerability in VLC Media Player's AVI file handling can cause the application to crash when opening a specially crafted AVI file. This affects VLC 3.0.11 users who open untrusted media files. The vulnerability results in denial of service but does not allow arbitrary code execution.

💻 Affected Systems

Products:

VideoLAN VLC Media Player

Versions: 3.0.11

Operating Systems: Windows, Linux, macOS, Other platforms running VLC

Default Config Vulnerable: ⚠️ Yes

Notes: All installations of VLC 3.0.11 are vulnerable regardless of configuration.

📦 What is this software?

Vlc Media Player by Videolan

View all CVEs affecting Vlc Media Player →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete application crash requiring restart, potentially disrupting media playback workflows or automated media processing systems.

🟠

Likely Case

Application crash when opening malicious AVI files, requiring user to restart VLC.

🟢

If Mitigated

No impact if patched version is used or if users avoid opening untrusted AVI files.

🌐 Internet-Facing: LOW - VLC is typically a client application, not internet-facing.

🏢 Internal Only: MEDIUM - Internal users could be affected if opening malicious files from internal sources.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires user interaction to open a malicious file. The fix commit shows the vulnerability is easily triggered.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 3.0.12 and later

Vendor Advisory: https://www.videolan.org/security/sb-vlc3012.html

Restart Required: Yes

Instructions:

1. Download latest VLC from videolan.org 2. Install over existing version 3. Restart system if prompted

🔧 Temporary Workarounds

Disable AVI file association

all

Prevent VLC from automatically opening AVI files

Windows: Control Panel > Default Programs > Associate file type > Remove .avi from VLC
Linux: Update mime-type associations to use different player for AVI

Use alternative media player for AVI files

all

Configure system to use different media player for AVI files

🧯 If You Can't Patch

Restrict user permissions to prevent downloading/opening untrusted media files
Implement application whitelisting to block execution of vulnerable VLC version

🔍 How to Verify

Check if Vulnerable:

Check VLC version in Help > About (Windows/Linux) or VLC menu > About VLC (macOS)

Check Version:

vlc --version (Linux/macOS) or check Help > About (Windows)

Verify Fix Applied:

Verify version is 3.0.12 or higher after update

📡 Detection & Monitoring

Log Indicators:

Application crash logs mentioning vlc.exe or libvlc
Windows Event Logs: Application Error with vlc.exe fault

Network Indicators:

Unusual AVI file downloads followed by VLC crashes

SIEM Query:

EventID=1000 AND SourceName='Application Error' AND ProcessName='vlc.exe'

📊 Metadata

CVE ID: CVE-2021-25804

CVSS v3 Score: 7.5 (HIGH)

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

CWE: CWE-476

Published: July 26, 2021

Last Updated: November 21, 2024

🔗 References

https://code.videolan.org/videolan/vlc-3.0/-/commit/a7f577ec26d35bbd7b2a3cda89d1b41bde69de9c Vendor Advisory
https://code.videolan.org/videolan/vlc-3.0/-/commit/a7f577ec26d35bbd7b2a3cda89d1b41bde69de9c Vendor Advisory

📤 Share & Export

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🔗 Related Vulnerabilities

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