NULL Pointer Dereference in GPAC MP4Box Causes DoS

Executive Summary

This vulnerability is a NULL pointer dereference in the TrackWriter handling component (filters/mux_isom.c) of GPAC MP4Box version 2.4. It occurs when the software processes a specially crafted MP4 file, which causes the program to attempt to access a memory location through a NULL pointer.

As a result, this leads to a Denial of Service (DoS) condition, meaning the application can crash or become unresponsive when handling such malicious files.

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Impact Analysis

The primary impact of this vulnerability is a Denial of Service (DoS). An attacker can exploit this by supplying a crafted MP4 file to the vulnerable GPAC MP4Box software, causing it to crash or stop functioning properly.

This can disrupt services or workflows that rely on GPAC MP4Box for processing MP4 files, potentially leading to downtime or loss of availability.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability can be detected by running GPAC MP4Box with DASH segmentation on a crafted MP4 file containing malformed metadata boxes such as mvcC or stsz boxes with extra bytes. The crash occurs due to a NULL pointer dereference in the TrackWriter handling component.

Using UndefinedBehaviorSanitizer (UBSan) during testing can help detect the issue, as it reports a "member access within null pointer" error at filters/mux_isom.c:6621:35.

A practical detection method is to execute MP4Box on suspicious or untrusted MP4 files with DASH segmentation enabled and observe if the application crashes.

Example command to test a file for triggering the vulnerability:

• mp4box -dash 1000 crafted_file.mp4

If MP4Box crashes or UBSan reports a null pointer dereference, the vulnerability is present.

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Mitigation Strategies

To mitigate this vulnerability immediately, avoid processing untrusted or crafted MP4 files with GPAC MP4Box, especially when using DASH segmentation.

If possible, update GPAC MP4Box to a version where this vulnerability is fixed or apply any available patches addressing the NULL pointer dereference in the TrackWriter handling.

As a temporary measure, restrict access to MP4Box usage to trusted users and files only, and monitor for crashes that may indicate exploitation attempts.

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