CVE-2025-25945

Executive Summary

CVE-2025-25945 is an information disclosure vulnerability in Bento4 v1.6.0-641, a popular multimedia library for MP4 file manipulation. The flaw resides in the Mp4Fragment.cpp and AP4_DescriptorFactory::CreateDescriptorFromStream at Ap4DescriptorFactory.cpp components, allowing an attacker to obtain sensitive information from the system or memory. The vulnerability has a CVSS score of 0.0 (likely unassigned or placeholder), and no public proof-of-concept (PoC) or patch is currently available. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the lack of a patch makes this a potential risk for systems using Bento4.

Supply Chain & Package Security

Bento4 is a C++ library distributed via GitHub and often integrated into media processing pipelines, video players, and streaming services. As an open-source component, it is not distributed through package managers like NPM, PyPI, Go, or Ruby, but it may be included as a submodule or dependency in larger projects. Organizations using Bento4 should audit their supply chain for this specific version and consider temporary mitigations until a patch is released.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned value. Based on the description (information disclosure via crafted MP4 files), a reasonable CVSS vector would be:

• Attack Vector (AV): Network (AV:N) – the vulnerability can be triggered by processing a malicious MP4 file.
• Attack Complexity (AC): Low (AC:L) – no special conditions required.
• Privileges Required (PR): None (PR:N) – no authentication needed.
• User Interaction (UI): Required (UI:R) – the victim must open or process the file.
• Scope (S): Unchanged (S:U) – the vulnerability affects only the vulnerable component.
• Confidentiality (C): High (C:H) – sensitive information can be leaked.
• Integrity (I): None (I:N) – no data modification.
• Availability (A): None (A:N) – no denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N Estimated Base Score: 6.5 (Medium)

Threat Level: Medium. The vulnerability requires user interaction and has no public exploit, but the lack of a patch increases risk for affected systems.

Deep Dive & Mechanics

The vulnerability is located in two files:

1. Mp4Fragment.cpp – This file handles MP4 fragment processing, which is part of the ISO Base Media File Format (ISOBMFF) used in streaming and fragmented MP4 files.
2. AP4_DescriptorFactory::CreateDescriptorFromStream in Ap4DescriptorFactory.cpp – This function parses descriptor streams from MP4 files, which are used to describe media properties (e.g., codecs, bitrates).

The issue likely involves improper bounds checking or memory handling when parsing malformed descriptor data. An attacker can craft a specially designed MP4 file with a corrupted descriptor stream that causes the library to read out-of-bounds memory or leak stack/heap data. This information could include:

• Memory addresses (useful for ASLR bypass)
• Sensitive data from other processes (if memory is shared)
• Internal library state

The vulnerability is triggered when the library processes the MP4 file, typically during parsing or fragmentation operations. No authentication is required, but user interaction (e.g., opening the file in a media player or processing it with a tool like mp4fragment) is necessary.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable code pattern. The vulnerable code likely looks like:

Vulnerable (Ap4DescriptorFactory.cpp):

AP4_Descriptor* AP4_DescriptorFactory::CreateDescriptorFromStream(AP4_ByteStream& stream) {
    // Read descriptor tag and length
    unsigned char tag;
    stream.ReadUI08(tag);
    unsigned int length;
    stream.ReadMU32(length); // No validation on length
    
    // Allocate buffer based on length
    unsigned char* data = new unsigned char[length];
    stream.Read(data, length); // Potential overflow if length is large
    
    // Process descriptor...
}

Patched (hypothetical):

AP4_Descriptor* AP4_DescriptorFactory::CreateDescriptorFromStream(AP4_ByteStream& stream) {
    unsigned char tag;
    stream.ReadUI08(tag);
    unsigned int length;
    stream.ReadMU32(length);
    
    // Validate length against remaining stream size
    AP4_Size remaining;
    stream.GetSize(remaining);
    if (length > remaining) {
        // Handle error
        return NULL;
    }
    
    unsigned char* data = new unsigned char[length];
    stream.Read(data, length);
    // Process descriptor...
}

The fix would involve adding length validation to prevent reading beyond the stream boundaries.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Bento4 v1.6.0-641 installed
• Ability to deliver a malicious MP4 file to the target

Exploitation Steps:

1. Craft Malicious MP4: Use a hex editor or custom script to create an MP4 file with a malformed descriptor stream. The descriptor length field should be set to a large value (e.g., 0xFFFFFFFF) to trigger out-of-bounds read.
2. Deliver File: Send the file via email, web download, or other means.
3. Trigger Processing: The victim must process the file using a Bento4-based tool (e.g., mp4fragment, mp4info, or a media player using the library).
4. Extract Data: The leaked memory may be visible in error messages, logs, or output. Use a debugger to capture the leaked data.

Example Python script to craft a malicious MP4:

import struct

def create_malicious_mp4():
    # Minimal MP4 file with malformed descriptor
    ftyp = b'\x00\x00\x00\x14ftypmp42\x00\x00\x00\x00mp42mp41'
    moov = b'\x00\x00\x00\x08moov'
    # Add a malformed descriptor with large length
    descriptor = b'\x03' + struct.pack('>I', 0xFFFFFFFF) + b'A'*100
    trak = b'\x00\x00\x00\x10trak' + descriptor
    moov += trak
    return ftyp + moov

with open('malicious.mp4', 'wb') as f:
    f.write(create_malicious_mp4())

Blue Team

Detection:

• Monitor for unusual MP4 files with abnormally large descriptor lengths.
• Use network monitoring to detect file transfers containing malformed MP4 structures.
• Implement file integrity monitoring for Bento4 binaries.

Hunting:

• Search for error logs containing "descriptor" or "fragment" errors.
• Analyze memory dumps for signs of out-of-bounds reads.

Mitigation:

• Restrict execution of Bento4 tools to trusted files only.
• Use sandboxing or containerization for media processing.
• Apply input validation at the application level (e.g., check file size before processing).

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available, but example for malicious file)
  • malicious.mp4: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • Unusual MP4 file transfers with large descriptor fields.
• Behavioral Indicators:
  • Bento4 processes crashing or producing unexpected output.
  • High memory usage during MP4 parsing.
• Log Entries:
  • AP4_DescriptorFactory::CreateDescriptorFromStream - error reading descriptor
  • Mp4Fragment - unexpected fragment size

Detection Engineering

YARA Rule

rule CVE_2025_25945_Bento4_InfoDisclosure {
    meta:
        description = "Detects malicious MP4 files exploiting CVE-2025-25945"
        author = "Valters IT"
        date = "2025-03-01"
        hash = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
    strings:
        $descriptor_tag = { 03 } // Descriptor tag
        $large_length = { FF FF FF FF } // 0xFFFFFFFF length
    condition:
        $descriptor_tag at 0 and $large_length
}

Sigma Rule

title: CVE-2025-25945 Bento4 Information Disclosure
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects exploitation attempts of CVE-2025-25945 via malformed MP4 files
author: Valters IT
date: 2025-03-01
logsource:
    category: file_event
    product: windows
detection:
    selection:
        Image|endswith: '\mp4fragment.exe'
        TargetFilename|endswith: '.mp4'
    condition: selection
falsepositives:
    - Legitimate large MP4 files
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-25945 Bento4 Malicious MP4 Download"; flow:to_client; file_store; fileext:"mp4"; content:"|03 FF FF FF FF|"; distance:0; within:5; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable or restrict Bento4-based tools until a patch is available.
2. Implement input validation at the application level to reject MP4 files with suspicious descriptor lengths.
3. Use a Web Application Firewall (WAF) or network filter to block known malicious patterns.

Long-term Fix:

• Monitor the Bento4 GitHub repository for a patch (https://github.com/axiomatic-systems/Bento4).
• Apply the patch as soon as it is released.
• Consider switching to an alternative library (e.g., FFmpeg, libav) if Bento4 is not updated.

Workarounds:

• Use a custom wrapper that validates MP4 files before passing them to Bento4.
• Run Bento4 in a sandboxed environment with limited privileges.

Valters IT
Securing Digital Frontiers