CVE-2025-70070

Executive Summary

CVE-2025-70070 is a denial-of-service (DoS) vulnerability in the Assimp library, version 6.0.2. The flaw resides in the FBXMeshGeometry.cpp file, specifically within the MeshGeometry::MeshGeometry() constructor. A remote attacker can trigger a crash by providing a specially crafted FBX file, leading to a null pointer dereference or similar memory corruption. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as high severity due to the ease of exploitation and potential for service disruption. No public exploit code or patch is currently available.

Supply Chain & Package Security

Assimp is a widely used open-source asset import library, integrated into numerous game engines, 3D modeling tools, and rendering pipelines. A DoS vulnerability in this library can cascade to any application that processes untrusted FBX files, making it a critical supply chain risk. Organizations using Assimp in their software stack should treat this as a high-priority issue.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Base Score: 7.5 (High)
• Attack Vector: Network (AV:N) – The attacker can send a malicious FBX file over the network.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – The victim does not need to click or perform any action beyond processing the file.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – The application crashes, causing a denial of service.

Threat Level: High. The vulnerability is remotely exploitable with low complexity and no user interaction, making it a prime target for automated attacks.

Deep Dive & Mechanics

The vulnerability is located in the MeshGeometry::MeshGeometry() constructor within FBXMeshGeometry.cpp. The constructor likely fails to properly validate input data, leading to a null pointer dereference or an out-of-bounds memory access when processing malformed FBX geometry data.

Root Cause Analysis:

• The constructor may assume that certain pointers or data structures are always valid.
• An attacker can craft an FBX file that omits required fields or provides invalid indices.
• When the constructor attempts to access these fields, it dereferences a null or invalid pointer, causing a segmentation fault.

Attack Vector:

1. The attacker creates a malicious FBX file with corrupted geometry data.
2. The file is loaded by an application using Assimp (e.g., a game engine, 3D viewer).
3. The MeshGeometry constructor is called, triggering the crash.

Impact:

• Denial of service: The application becomes unresponsive or crashes.
• Potential for further exploitation: While not confirmed, memory corruption vulnerabilities can sometimes be leveraged for code execution.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code path.

Vulnerable Code (Assimp v6.0.2 - FBXMeshGeometry.cpp):

// Hypothetical vulnerable code
MeshGeometry::MeshGeometry(const Mesh& mesh) {
    // Assume mesh.mVertices is always valid
    for (size_t i = 0; i < mesh.mVertices->size(); ++i) {
        // Process vertices
    }
}

Patched Code (Hypothetical):

MeshGeometry::MeshGeometry(const Mesh& mesh) {
    if (mesh.mVertices == nullptr) {
        // Handle error gracefully
        return;
    }
    for (size_t i = 0; i < mesh.mVertices->size(); ++i) {
        // Process vertices
    }
}

The patch would add null pointer checks and input validation before accessing any data structures.

Exploitation & Lab Setup

Red Team (Exploitation)

Objective: Craft a malicious FBX file that triggers the DoS.

Tools Required:

• Python 3.x
• struct module for binary data manipulation
• A vulnerable application using Assimp (e.g., a custom test harness)

Exploit Script (Python):

import struct

def create_malicious_fbx(output_path):
    # Minimal FBX header
    header = b"Kaydara FBX Binary  \x00\x1a\x00"
    # Placeholder for a malformed geometry node
    # This is a simplified example; real FBX is more complex
    malformed_data = b"\x00" * 100  # Corrupted data
    with open(output_path, "wb") as f:
        f.write(header)
        f.write(malformed_data)

if __name__ == "__main__":
    create_malicious_fbx("malicious.fbx")

Usage:

1. Run the script to generate malicious.fbx.
2. Load the file in a vulnerable application (e.g., ./assimp_viewer malicious.fbx).
3. Observe the crash.

Blue Team (Defense)

Detection:

• Monitor for crashes in applications using Assimp.
• Use file integrity monitoring to detect unexpected FBX files.
• Implement network-level filtering for FBX files from untrusted sources.

Mitigation:

• Isolate applications that process untrusted FBX files in sandboxed environments.
• Apply strict input validation before passing files to Assimp.
• Use a Web Application Firewall (WAF) to block malicious file uploads.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Placeholder – generate after creating the malicious file)
  • malicious.fbx: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Patterns:
  • Unusual FBX file uploads to web applications.
  • Repeated crashes in applications using Assimp.
• Behavioral:
  • Segmentation faults in processes loading FBX files.
  • Application logs showing "Null pointer dereference" or "Access violation".

Detection Engineering

YARA Rule

rule CVE_2025_70070_Assimp_FBX_DoS {
    meta:
        description = "Detects malicious FBX files targeting CVE-2025-70070"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $fbx_header = "Kaydara FBX Binary"
        $corrupt_pattern = { 00 00 00 00 00 00 00 00 } // Example pattern
    condition:
        $fbx_header at 0 and #corrupt_pattern > 10
}

Sigma Rule

title: CVE-2025-70070 Assimp FBX DoS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects crashes caused by malicious FBX files
logsource:
    category: application
    product: assimp
detection:
    selection:
        EventID: 1000  # Application Error (Windows)
        Application: "assimp*"
        ExceptionCode: 0xc0000005  # Access violation
    condition: selection
falsepositives:
    - Legitimate corrupted files
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-70070 Assimp FBX DoS Attempt"; flow:to_server; content:"Kaydara FBX Binary"; depth:20; content:"|00 00 00 00|"; distance:0; within:100; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable FBX processing in applications using Assimp until a patch is available.
2. Implement input validation – Use a pre-processor to validate FBX files before passing them to Assimp.
3. Apply workarounds – If possible, use an alternative library for FBX parsing.

Long-Term Fix:

• Monitor the Assimp repository for a patch (expected in v6.0.3 or later).
• Once patched, update to the latest version immediately.
• Conduct a code review of the FBXMeshGeometry.cpp file to identify similar vulnerabilities.

Compensating Controls:

• Run applications processing FBX files in a sandboxed environment.
• Use memory protection mechanisms (e.g., ASLR, DEP).
• Implement rate limiting for file uploads to reduce DoS impact.

Valters IT
DevSecOps & Cyber Threat Intelligence

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