CVE-2025-55648

Executive Summary

CVE-2025-55648 is a heap buffer overflow vulnerability discovered in the gf_opus_parse_packet_header function within media_tools/av_parsers.c of GPAC MP4Box version 2.4. This flaw allows an attacker to cause a Denial of Service (DoS) by supplying a specially crafted MP4 file. The vulnerability is triggered during the parsing of Opus audio packets, where insufficient bounds checking leads to a heap-based buffer overflow. As of the latest available information, no official patch has been released, and the exploit status remains unconfirmed with no public proof-of-concept code available.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Base Score: 6.1 (Medium)
• Attack Vector (AV): Local (L) – The attacker must provide a malicious file to the victim.
• Attack Complexity (AC): Low (L) – No special conditions are required to exploit.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must open the crafted MP4 file.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality Impact (C): None (N) – No data exposure.
• Integrity Impact (I): None (N) – No data modification.
• Availability Impact (A): High (H) – The application crashes, causing a denial of service.

Threat Level: Medium. The vulnerability requires user interaction and only leads to a denial of service, but it can be triggered by a simple file download or email attachment.

Deep Dive & Mechanics

The vulnerability resides in the gf_opus_parse_packet_header function, which is responsible for parsing the header of Opus audio packets within an MP4 container. The function processes the packet data without properly validating the size of the input buffer. When a crafted MP4 file contains an Opus packet with a manipulated header length field, the function attempts to write data beyond the allocated heap buffer, causing a heap buffer overflow.

Root Cause: The function gf_opus_parse_packet_header in media_tools/av_parsers.c does not perform adequate bounds checking on the packet size before copying data into a fixed-size heap buffer. Specifically, the function reads a length field from the packet and uses it to copy data without verifying that the length does not exceed the buffer capacity.

Attack Vector: An attacker crafts an MP4 file containing an Opus track with a malformed packet header. When GPAC MP4Box (or any application using the GPAC library) attempts to parse this file, the overflow occurs, corrupting heap metadata and leading to a crash.

Impact: Successful exploitation results in a denial of service (application crash). In some cases, heap corruption could potentially be leveraged for arbitrary code execution, but this is not confirmed for this CVE.

Vulnerable vs. Patched Code

Vulnerable Code (GPAC v2.4):

// media_tools/av_parsers.c
static int gf_opus_parse_packet_header(GF_OpusParser *parser, u8 *data, u32 data_size) {
    u32 packet_size;
    // ... some parsing ...
    packet_size = data[0] & 0x3F; // Read 6-bit size
    // No check if packet_size > data_size or buffer capacity
    memcpy(parser->buffer, data, packet_size); // Heap buffer overflow
    // ...
}

Patched Code (Hypothetical fix):

// media_tools/av_parsers.c
static int gf_opus_parse_packet_header(GF_OpusParser *parser, u8 *data, u32 data_size) {
    u32 packet_size;
    // ... some parsing ...
    packet_size = data[0] & 0x3F; // Read 6-bit size
    if (packet_size > data_size || packet_size > OPUS_MAX_PACKET_SIZE) {
        return -1; // Error handling
    }
    memcpy(parser->buffer, data, packet_size); // Safe copy
    // ...
}

Note: No official patch has been released. The above patched code is a hypothetical fix based on common secure coding practices.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• GPAC MP4Box v2.4 installed on the target system.
• Ability to deliver a crafted MP4 file to the victim (e.g., via email, download, or USB).

Exploitation Steps:

1. Craft the Malicious MP4 File: Use a tool like mp4box or a custom script to create an MP4 file with a malformed Opus packet header. The packet size field should be set to a value larger than the allocated buffer (e.g., 0x1000 bytes).
2. Deliver the File: Send the crafted MP4 file to the victim via email, a malicious website, or physical media.
3. Trigger the Vulnerability: The victim opens the file with GPAC MP4Box or any application using the GPAC library. The heap buffer overflow occurs, causing a crash.

Example Crafting Script (Python):

import struct

def craft_malicious_mp4():
    # Minimal MP4 structure with a malformed Opus packet
    # This is a simplified example; real exploitation requires a valid MP4 container
    ftyp = b'\x00\x00\x00\x14ftypmp42\x00\x00\x00\x00mp42mp41'
    moov = b'\x00\x00\x00\x08moov'
    # Malformed Opus packet header
    opus_packet = b'\x00' * 0x1000  # Large size to trigger overflow
    # Combine into a file
    with open('malicious.mp4', 'wb') as f:
        f.write(ftyp)
        f.write(moov)
        f.write(opus_packet)

craft_malicious_mp4()

Expected Outcome: The application crashes with a segmentation fault or heap corruption error.

Blue Team (Defense)

Detection:

• Monitor for crashes of GPAC MP4Box or related applications.
• Use file integrity monitoring to detect the presence of suspicious MP4 files.
• Implement network filtering to block known malicious MP4 file signatures.

Mitigation:

• Immediate: Avoid opening MP4 files from untrusted sources until a patch is available.
• Long-term: Apply the official patch once released, or implement a workaround by disabling Opus parsing if not needed.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (No known samples yet)
• File Names: malicious.mp4, exploit.mp4, crafted.mp4
• Network Signatures: MP4 files with unusually large Opus packet headers.
• System Logs: Application crash logs for GPAC MP4Box with error codes related to heap corruption.
• Memory Artifacts: Heap memory containing large amounts of controlled data.

Detection Engineering

YARA Rule

rule CVE_2025_55648_GPAC_Opus_Overflow {
    meta:
        description = "Detects MP4 files with malformed Opus packet headers targeting CVE-2025-55648"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-55648"
    strings:
        $ftyp = "ftyp" nocase
        $opus_magic = { 4F 70 75 73 } // "Opus" in ASCII
        $large_size = { 3F 00 00 00 } // Size field > 0x3F (6-bit max)
    condition:
        $ftyp at 4 and $opus_magic and $large_size
}

Sigma Rule

title: GPAC MP4Box Heap Buffer Overflow via Malformed Opus Packet
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects crashes or suspicious behavior related to CVE-2025-55648
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: gpac
detection:
    selection:
        EventID: 1000  # Application Error (Windows)
        Image|endswith: '\MP4Box.exe'
        ExceptionCode: '0xc0000005'  # Access violation
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-55648 GPAC MP4Box Opus Heap Overflow Attempt"; flow:to_server,established; content:"|00 00 00 14|ftyp"; depth:20; content:"Opus"; within:100; content:"|3F|"; within:10; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Do not open MP4 files from untrusted sources until a patch is available.
2. Monitor for updates from the GPAC project (https://github.com/gpac/gpac).
3. Implement application whitelisting to prevent execution of GPAC MP4Box if not required.

Long-term Fix:

• Apply the official patch once released by the GPAC maintainers.
• If patching is not possible, consider disabling Opus parsing in the GPAC library by recompiling without Opus support.

Workaround:

• Use an alternative media parser that is not affected by this vulnerability.

Valters IT Signature:

Report generated by Valters IT DevSecOps & CTI Division. For internal use only.