CVE-2025-55643

Executive Summary

CVE-2025-55643 is a NULL pointer dereference vulnerability in the GPAC MP4Box tool, specifically within the TrackWriter handling component (filters/mux_isom.c). The flaw allows an attacker to cause a Denial of Service (DoS) by supplying a crafted MP4 file. The vulnerability affects GPAC MP4Box version 2.4 and potentially earlier versions. No patch is currently available, and no public proof-of-concept (PoC) code has been released. The CVSS score is 0.0 due to incomplete scoring data, but the vulnerability is classified as a DoS issue with a local attack vector requiring user interaction.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the GPAC multimedia framework, which is distributed as a standalone binary or source code.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (AV:L) – The attacker must have local access to the system or trick a user into opening a malicious file.
• Attack Complexity (AC): Low (AC:L) – No special conditions are required to exploit the vulnerability.
• Privileges Required (PR): None (PR:N) – No authentication is needed.
• User Interaction (UI): Required (UI:R) – The victim must open the crafted MP4 file with MP4Box.
• Scope (S): Unchanged (S:U) – The exploit does not affect other components.
• Confidentiality (C): None (C:N) – No data is exposed.
• Integrity (I): None (I:N) – No data is modified.
• Availability (A): High (A:H) – The application crashes, causing a denial of service.

Threat Level: Medium (due to DoS impact and user interaction requirement)

Deep Dive & Mechanics

The vulnerability resides in the TrackWriter handling component within filters/mux_isom.c. When processing a crafted MP4 file, the code attempts to dereference a pointer that has not been properly initialized, leading to a NULL pointer dereference. This causes the application to crash, resulting in a Denial of Service.

The root cause is likely a missing null check before using a pointer returned from a function or allocated memory. In the TrackWriter logic, when parsing the MP4 file's track metadata, a pointer to a structure (e.g., GF_ISOMTrack or similar) is used without verifying that it is not NULL. An attacker can craft an MP4 file that triggers this condition, causing the crash.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code path is identified as:

Vulnerable Code (filters/mux_isom.c, v2.4):

// Hypothetical vulnerable snippet
GF_ISOMTrack *track = gf_isom_get_track(movie, track_num);
// Missing NULL check
track->some_field = value; // NULL pointer dereference if track is NULL

Patched Code (Hypothetical):

GF_ISOMTrack *track = gf_isom_get_track(movie, track_num);
if (track == NULL) {
    // Handle error gracefully
    return GF_BAD_PARAM;
}
track->some_field = value;

Exploitation & Lab Setup

Red Team (Attacker)

1. Craft a malicious MP4 file that triggers the NULL pointer dereference. This can be done by manipulating the MP4 file structure to cause gf_isom_get_track to return NULL.
2. Deliver the file to the victim via email, download, or other means.
3. Victim executes MP4Box -info malicious.mp4 or similar command.
4. Result: MP4Box crashes, causing a Denial of Service.

Example command:

MP4Box -info malicious.mp4

Blue Team (Defender)

1. Monitor for crashes of MP4Box processes.
2. Analyze crash dumps to identify the crafted MP4 file.
3. Block known malicious MP4 files using file hashes or YARA rules.
4. Restrict execution of MP4Box to trusted users only.

Indicators of Compromise (IOCs)

• File Hashes: (No known samples yet)
• Process Name: MP4Box crashing with a NULL pointer dereference.
• Event Logs: Application crash events with exception code 0xC0000005 (Access Violation).
• Network Traffic: None (local file-based attack).

Detection Engineering

YARA Rule

rule CVE_2025_55643_MP4Box_NULL_Deref {
    meta:
        description = "Detects crafted MP4 files targeting CVE-2025-55643"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-55643"
    strings:
        $mp4_magic = { 00 00 00 18 66 74 79 70 } // ftyp box
        $null_trigger = { 00 00 00 00 } // Potential null pointer trigger
    condition:
        $mp4_magic and #null_trigger > 5
}

Sigma Rule

title: CVE-2025-55643 MP4Box NULL Pointer Dereference
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects MP4Box crashes due to NULL pointer dereference
author: Valters IT
logsource:
    category: application
    product: windows
    service: application
detection:
    selection:
        EventID: 1000
        ProviderName: 'Application Error'
        ApplicationName: 'MP4Box.exe'
        ExceptionCode: '0xc0000005'
    condition: selection
falsepositives:
    - Unknown
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-55643 MP4Box NULL Pointer Dereference"; flow:to_client,established; file_store; filemagic:"MP4"; content:"|00 00 00 18 66 74 79 70|"; distance:0; within:8; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• No patch available – Monitor GPAC repository for updates.
• Mitigation: Avoid opening untrusted MP4 files with MP4Box.
• Workaround: Use alternative tools for MP4 processing until a patch is released.
• Detection: Implement YARA and Sigma rules to detect malicious files and crashes.

Valters IT
Securing Digital Frontiers