CVE-2024-53425

Executive Summary

CVE-2024-53425 is a heap-buffer-overflow vulnerability discovered in the Assimp library version 5.4.3. The flaw resides in the SkipSpacesAndLineEnd function, which is used during the parsing of MD5 model files. When processing a specially crafted, malformed MD5 file, the function performs an out-of-bounds read, leading to a potential application crash. This is a denial-of-service (DoS) vulnerability that can be triggered by a local user or remotely if an application using Assimp loads a malicious file. The vulnerability has a CVSS score of 0.0 (pending analysis), but based on the description, it is a high-severity DoS issue. No public exploit code or patch is currently available.

Supply Chain & Package Security

Assimp (Open Asset Import Library) is a widely used library for importing various 3D model formats. It is a dependency for many applications in game development, 3D modeling, and rendering. This vulnerability affects the supply chain of any software that bundles or dynamically links to the vulnerable version of Assimp. Users of such software are at risk of application crashes when loading untrusted MD5 model files.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (AV:L) - The attacker must have the ability to provide a malicious file to the victim.
• Attack Complexity (AC): Low (AC:L) - No special conditions are required to trigger the vulnerability.
• Privileges Required (PR): None (PR:N) - No authentication is needed.
• User Interaction (UI): Required (UI:R) - The victim must open the malicious file.
• Scope (S): Unchanged (S:U) - The vulnerability does not affect other components.
• Confidentiality (C): None (C:N) - No data is exposed.
• Integrity (I): None (I:N) - No data is modified.
• Availability (A): High (A:H) - The application crashes, causing a denial of service.

Threat Level: High (Denial of Service)

Deep Dive & Mechanics

The vulnerability is a classic heap-buffer-overflow. The SkipSpacesAndLineEnd function in Assimp is responsible for parsing whitespace and line endings in MD5 model files. When a malformed file is provided, the function fails to properly validate the bounds of the input buffer. This leads to reading memory beyond the allocated heap buffer.

The root cause is likely an off-by-one error or a missing length check in the loop that iterates through the input string. The function may continue reading past the null terminator or the end of the allocated buffer, causing an out-of-bounds read. This can corrupt heap metadata or cause a segmentation fault.

The attack vector is simple: an attacker crafts a malicious MD5 file that triggers the overflow. The victim loads this file using an application that relies on Assimp (e.g., a 3D viewer, game engine, or converter). The application then crashes.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, the vulnerable code is in the SkipSpacesAndLineEnd function within the MD5 loader of Assimp 5.4.3. A hypothetical patch would add a bounds check before accessing the input buffer.

Vulnerable Code (Conceptual):

void SkipSpacesAndLineEnd(const char*& pCur) {
    while (*pCur == ' ' || *pCur == '\t' || *pCur == '\r' || *pCur == '\n') {
        ++pCur;
    }
}

Patched Code (Conceptual):

void SkipSpacesAndLineEnd(const char*& pCur, const char* pEnd) {
    while (pCur < pEnd && (*pCur == ' ' || *pCur == '\t' || *pCur == '\r' || *pCur == '\n')) {
        ++pCur;
    }
}

Exploitation & Lab Setup

Red Team

Objective: Trigger a denial of service by crafting a malicious MD5 file.

Lab Setup:

1. Install Assimp 5.4.3 on a test system (e.g., Ubuntu 22.04).
2. Create a simple C++ program that loads an MD5 file using Assimp.
3. Craft a malformed MD5 file that triggers the overflow.

Crafting the Malicious File: The exact payload is unknown, but the file should contain a long sequence of whitespace characters (spaces, tabs, newlines) without a null terminator, or a string that causes the parser to read beyond the buffer.

Example Malformed MD5 File (conceptual):

MD5Version 10
commandline ""

numJoints 0
numMeshes 0

joints {
}

mesh {
    // Very long whitespace line to trigger overflow
                                                                                                   
}

Execution:

g++ -o load_md5 load_md5.cpp -lassimp
./load_md5 malicious.md5

Expected Result: The application crashes with a segmentation fault.

Blue Team

Detection:

• Monitor for crashes in applications that use Assimp.
• Use file integrity monitoring to detect the introduction of suspicious MD5 files.
• Implement application whitelisting to prevent untrusted applications from loading MD5 files.

Mitigation:

• Update Assimp to a patched version when available.
• Use a sandbox or container to isolate applications that process untrusted 3D models.
• Validate MD5 files before loading them (e.g., check file size, structure).

Indicators of Compromise (IOCs)

• File Hashes: (None available, but any MD5 file that causes a crash is suspicious)
• Process Behavior: Application crash (segmentation fault) in a process using libassimp.so.
• Network Traffic: None (local file-based attack).
• Logs: System logs showing a segfault in an application using Assimp.

Detection Engineering

YARA Rule

rule CVE_2024_53425_Assimp_Heap_Overflow {
    meta:
        description = "Detects malformed MD5 files that may trigger CVE-2024-53425"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-53425"
    strings:
        $md5_header = "MD5Version"
        $long_whitespace = /[ \t\r\n]{1000,}/  // Very long whitespace sequence
    condition:
        $md5_header at 0 and #long_whitespace > 0
}

Sigma Rule

title: CVE-2024-53425 Assimp Heap Buffer Overflow
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects application crashes caused by CVE-2024-53425
author: Valters IT
date: 2024-01-01
logsource:
    category: application
    product: linux
detection:
    selection:
        EventID: 11  # Linux crash event (e.g., segfault)
        Image|endswith: '/assimp'  # Or any application using libassimp
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-53425 Assimp MD5 Heap Overflow"; flow:to_server,established; content:"MD5Version"; nocase; pcre:"/[ \t\r\n]{1000,}/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Avoid loading untrusted MD5 model files in applications that use Assimp 5.4.3.
2. Short-term: Monitor the Assimp project for a patch. Apply it as soon as it is released.
3. Long-term: Implement input validation for all 3D model files before processing them with Assimp. Consider using a sandboxed environment for parsing untrusted files.
4. Workaround: If patching is not possible, modify the source code of the application to add bounds checking before calling SkipSpacesAndLineEnd.

Valters IT
DevSecOps & Cyber Threat Intelligence