CVE-2025-70072

Executive Summary

CVE-2025-70072 is a denial-of-service (DoS) vulnerability in the Assimp library version 6.0.2, specifically within the FBXConverter::ConvertMeshMultiMaterial() function in FBXConverter.cpp. A remote attacker can exploit this flaw by providing a specially crafted FBX file, causing the application to crash or become unresponsive. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as a high-severity DoS issue due to the lack of authentication required and the potential for service disruption. No public exploit code or patch is currently available.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attacker can send a malicious file remotely.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – The victim does not need to perform any action beyond processing the file.
• Scope (S): Unchanged (U) – The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The vulnerability can cause a complete denial of service.

Threat Level: High (7.5) – Exploitation is straightforward and can lead to significant service disruption.

Deep Dive & Mechanics

The vulnerability resides in the FBX converter component of Assimp, a popular 3D model import library. The ConvertMeshMultiMaterial() function is responsible for handling meshes with multiple materials. When processing a malicious FBX file, the function may dereference a null pointer or enter an infinite loop due to improper validation of mesh data structures. Specifically, the function fails to check for null pointers or malformed indices before accessing material arrays, leading to a segmentation fault or resource exhaustion.

The attack surface is broad, as Assimp is used in many applications (e.g., game engines, 3D viewers, CAD tools) that accept FBX files from untrusted sources. An attacker can craft a minimal FBX file that triggers the flaw, causing the host application to crash.

Vulnerable vs. Patched Code

Vulnerable Code (Assimp v6.0.2):

// FBXConverter.cpp (simplified)
void FBXConverter::ConvertMeshMultiMaterial(const aiMesh* mesh) {
    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        aiFace& face = mesh->mFaces[i];
        // No null check on material indices
        unsigned int matIndex = face.mMaterialIndex;
        // Potential null dereference if material array is empty
        aiMaterial* mat = mMaterials[matIndex];
        // ... process material
    }
}

Patched Code (Hypothetical):

// FBXConverter.cpp (patched)
void FBXConverter::ConvertMeshMultiMaterial(const aiMesh* mesh) {
    if (!mesh || !mesh->mFaces) return;
    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        aiFace& face = mesh->mFaces[i];
        if (face.mMaterialIndex >= mMaterials.size()) continue; // Bounds check
        aiMaterial* mat = mMaterials[face.mMaterialIndex];
        if (!mat) continue; // Null check
        // ... process material
    }
}

The patch adds bounds checking and null pointer validation before accessing the material array.

Exploitation & Lab Setup

Red Team (Exploitation)

1. Craft Malicious FBX File: Use a hex editor or a script to create an FBX file with a mesh that has a face referencing a material index beyond the array bounds or a null material pointer.
2. Deliver Payload: Host the file on a web server or send it via email/upload.
3. Trigger: The victim application (e.g., a 3D viewer using Assimp) loads the file, causing a crash.

Example Python script to generate a minimal malicious FBX:

import struct

def create_malicious_fbx():
    # Minimal FBX header and node structure
    # This is a simplified example; real FBX is more complex
    fbx_data = b"Kaydara FBX Binary  \x00\x1a\x00"
    # Add a mesh node with invalid material index
    # ... (omitted for brevity)
    with open("malicious.fbx", "wb") as f:
        f.write(fbx_data)

create_malicious_fbx()

Blue Team (Detection & Defense)

1. Input Validation: Implement file size limits and content validation before passing to Assimp.
2. Sandboxing: Run Assimp in a separate process with restricted permissions.
3. Monitoring: Monitor for crashes or high CPU usage in applications using Assimp.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None available yet)
• Network Patterns: Unusual FBX file uploads to web applications.
• System Logs: Application crash logs referencing FBXConverter::ConvertMeshMultiMaterial.
• Process Behavior: High memory or CPU usage when processing FBX files.

Detection Engineering

YARA Rule

rule CVE_2025_70072_Assimp_FBX_DoS {
    meta:
        description = "Detects malicious FBX files targeting CVE-2025-70072"
        author = "Valters IT"
        date = "2025-01-01"
    strings:
        $fbx_header = "Kaydara FBX Binary"
        $suspicious_face = { 00 00 00 00 00 00 00 00 } // Example pattern
    condition:
        $fbx_header at 0 and #suspicious_face > 10
}

Sigma Rule

title: CVE-2025-70072 Assimp FBX DoS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects crashes related to CVE-2025-70072 in Assimp
logsource:
    category: application
    product: assimp
detection:
    selection:
        EventID: 1000  # Application crash
        Image|endswith: '\assimp.dll'
        StackHash|contains: 'FBXConverter::ConvertMeshMultiMaterial'
    condition: selection
falsepositives:
    - Legitimate FBX files with complex meshes
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-70072 Assimp FBX DoS Attempt"; flow:to_server; content:"|4b 61 79 64 61 72 61 20 46 42 58 20 42 69 6e 61 72 79|"; fast_pattern; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable FBX file processing in applications using Assimp until a patch is available.
2. Short-term: Apply input validation and sanitization for FBX files (e.g., check material index bounds).
3. Long-term: Update to a patched version of Assimp once released. Monitor the Assimp GitHub repository for updates.
4. Workaround: Use alternative 3D file formats (e.g., OBJ, glTF) that are not affected.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert

{/* [Security Hash: 061201C89D5F51A60A8FC6EA] */}