Out-of-Bounds Read in GPAC MP4Box via vobsub_read_idx

Executive Summary

This vulnerability exists in GPAC 26.03-DEV, specifically in the function vobsub_read_idx within the file /src/media_tools/vobsub.c of the MP4Box component. It involves an out-of-bounds read caused by improper handling of the argument num_langs, which can exceed the bounds of a fixed-size array (langs[32]). This happens when a crafted subtitle index (.idx) file contains repeated language declarations, causing num_langs to surpass the array size and leading to out-of-bounds memory access.

The vulnerability can be triggered locally by providing a malicious subtitle file, potentially causing crashes or denial of service in applications using GPAC or MP4Box. The issue has been publicly disclosed and fixed by applying boundary checks and logic improvements to prevent out-of-bounds access.

Useful 0 Not Useful 0

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.

Useful 0 Not Useful 0

Impact Analysis

Exploiting this vulnerability can lead to out-of-bounds memory reads, which may cause application crashes (segmentation faults) or denial of service when processing malicious subtitle files. Since the attack requires local access and crafted subtitle files, it could disrupt the normal operation of multimedia applications like GPAC or MP4Box on your system.

Useful 0 Not Useful 0

Detection Guidance

This vulnerability involves an out-of-bounds read in the vobsub_read_idx function of GPAC's MP4Box component, triggered by a crafted subtitle (.idx) file with excessive or duplicate language entries.

Detection can focus on identifying usage of vulnerable GPAC versions processing suspicious or malformed .idx subtitle files that contain repeated 'id:' declarations exceeding 32 entries.

Since the attack requires local execution and malformed subtitle files, you can detect attempts by monitoring for crashes or segmentation faults in GPAC or MP4Box processes when opening subtitle files.

Suggested commands include:

• Use process monitoring tools (e.g., `ps`, `top`, `htop`) to watch for GPAC or MP4Box crashes.
• Check logs for segmentation faults or crashes related to GPAC or MP4Box.
• Manually inspect .idx subtitle files for repeated 'id:' entries exceeding 32 using commands like `grep -c '^id:' file.idx`.
• Run GPAC or MP4Box in a controlled environment with suspicious .idx files to observe abnormal behavior or crashes.

Useful 0 Not Useful 0

Mitigation Strategies

The primary mitigation step is to apply the official patches that fix the out-of-bounds read vulnerability in GPAC's MP4Box component.

The patches include boundary checks on the num_langs argument and improvements in VobSub parsing logic to prevent out-of-bounds memory access.

Additional immediate steps include:

• Avoid processing untrusted or malformed .idx subtitle files that may contain excessive or duplicate language entries.
• Restrict local access to systems running vulnerable GPAC versions to prevent local exploitation.
• Monitor for crashes or abnormal behavior in GPAC or MP4Box and investigate suspicious subtitle files.

Applying the patch identified by commit aa0fb77 (Resource 1) is the best practice to fully resolve this issue.

Useful 0 Not Useful 0