CVE-2025-70069

Executive Summary

CVE-2025-70069 is a denial-of-service (DoS) vulnerability discovered in the Assimp library (Open Asset Import Library) version 6.0.2. The flaw resides in the FBXConverter.cpp file, specifically within the ConvertMeshMultiMaterial() method. A remote attacker can trigger a null pointer dereference or an infinite loop by providing a specially crafted FBX file, leading to a crash or resource exhaustion. No patch or public proof-of-concept (PoC) is currently available. The vulnerability has a CVSS score of 0.0 due to incomplete scoring data, but based on the description, it is assessed as a high-severity DoS issue.

Supply Chain & Package Security

Assimp is a widely used library for importing 3D models in various formats (FBX, OBJ, COLLADA, etc.). It is integrated into numerous applications, game engines, and rendering pipelines. A DoS vulnerability in Assimp can affect any downstream software that processes user-supplied FBX files without proper validation. This includes desktop applications, web services, and cloud-based rendering platforms. The lack of a patch increases the risk for supply chain attacks, where an attacker could embed a malicious FBX file in a game mod, 3D asset repository, or web upload service.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which typically indicates incomplete or missing scoring data. Based on the vulnerability description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The attacker can send a malicious FBX file over the network.
• 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 click or interact beyond loading the file.
• Scope (S): Unchanged (U) – The vulnerability affects only the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – The service or application becomes unavailable.

Threat Level: High (7.5) – The vulnerability is remotely exploitable with low complexity and no user interaction, leading to a denial of service.

Deep Dive & Mechanics

The vulnerability is located in the FBXConverter.cpp file, in the ConvertMeshMultiMaterial() method. This method is responsible for converting FBX meshes that have multiple materials assigned to different faces. The flaw likely involves improper handling of null pointers or malformed data structures within the FBX file.

Technical Analysis:

1. Entry Point: When Assimp loads an FBX file, it parses the binary or ASCII FBX data and constructs internal geometry and material structures.
2. Vulnerable Function: ConvertMeshMultiMaterial() iterates over the faces of a mesh and groups them by material index. It then creates sub-meshes for each material.
3. Root Cause: A crafted FBX file can cause the function to dereference a null pointer or enter an infinite loop. This could be triggered by:
   • A material index that is out of bounds or negative.
   • A face that references a non-existent material.
   • A malformed geometry data structure that causes the loop to never terminate.
4. Impact: The application crashes (null pointer dereference) or hangs (infinite loop), resulting in a denial of service.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is in Assimp v.6.0.2. The following is a hypothetical comparison based on the vulnerability description.

Vulnerable Code (v.6.0.2):

// FBXConverter.cpp (simplified)
void FBXConverter::ConvertMeshMultiMaterial(const aiMesh* mesh) {
    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        const aiFace& face = mesh->mFaces[i];
        unsigned int matIndex = face.mMaterialIndex; // Could be out of bounds
        // No validation of matIndex
        // ...
        // Potential null pointer dereference if material array is not properly initialized
        const aiMaterial* mat = mMaterials[matIndex];
        // ...
    }
}

Patched Code (Hypothetical):

// FBXConverter.cpp (patched)
void FBXConverter::ConvertMeshMultiMaterial(const aiMesh* mesh) {
    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        const aiFace& face = mesh->mFaces[i];
        unsigned int matIndex = face.mMaterialIndex;
        // Validate material index
        if (matIndex >= mMaterials.size() || mMaterials[matIndex] == nullptr) {
            // Skip or handle error gracefully
            continue;
        }
        const aiMaterial* mat = mMaterials[matIndex];
        // ...
    }
}

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Cause a denial of service in an application using Assimp v.6.0.2 by providing a malicious FBX file.

Lab Setup:

1. Target Application: Any application that uses Assimp to load FBX files (e.g., a 3D viewer, game engine, or web service).
2. Attacker Machine: Kali Linux or any system with Python and a hex editor.

Steps:

1. Craft Malicious FBX File: Create a minimal FBX file with a malformed mesh that triggers the vulnerability. Since no public PoC exists, the attacker would need to reverse-engineer the vulnerable code to craft the file. A simple approach is to set a material index to a very large number or a negative value (if the parser allows it).
2. Deliver the File: Send the malicious FBX file to the target via email, web upload, or direct file transfer.
3. Trigger the Vulnerability: The target application loads the FBX file, causing a crash or hang.

Example Malicious FBX (Hex):

; FBX 7.4.0 project file
; (Simplified - actual FBX is binary)
; Set material index to 999999
Faces: *1 {
    a: 0, 1, 2, 999999
}

Blue Team (Defender)

Objective: Detect and block malicious FBX files targeting CVE-2025-70069.

Detection Strategy:

1. File Validation: Implement pre-processing validation of FBX files before passing them to Assimp. Check for out-of-bounds material indices, malformed geometry, and other anomalies.
2. Sandboxing: Run Assimp in a sandboxed environment with limited resources to prevent DoS from affecting the main application.
3. Monitoring: Monitor application logs for crashes or hangs related to FBX parsing.

Mitigation:

• Temporary Workaround: Disable FBX support or use an alternative library until a patch is released.
• Input Sanitization: Use a custom FBX parser to validate the file structure before passing it to Assimp.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): None available (no public PoC).
• Network Indicators: FBX files with unusually large material indices or malformed face data.
• Behavioral Indicators:
  • Application crash with a null pointer dereference in FBXConverter.cpp.
  • Application hang (infinite loop) when loading an FBX file.
  • High CPU usage during FBX parsing.

Detection Engineering

YARA Rule

rule CVE_2025_70069_Assimp_FBX_DoS {
    meta:
        description = "Detects malicious FBX files targeting CVE-2025-70069"
        author = "Valters IT"
        date = "2025-01-01"
        hash = "unknown"
    strings:
        $fbx_header = "Kaydara FBX Binary"
        $large_mat_index = /mMaterialIndex[^\x00]*\x{FF\xFF\xFF\xFF}/ // 4-byte large value
    condition:
        $fbx_header and $large_mat_index
}

Sigma Rule

title: CVE-2025-70069 Assimp FBX DoS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects application crashes or hangs caused by malicious FBX files
author: Valters IT
logsource:
    category: application
    product: assimp
detection:
    selection:
        EventID: 1000  # Application Error (Windows)
        Image: '*assimp*'
        ExceptionCode: 0xc0000005  # Access violation
    condition: selection
falsepositives:
    - Legitimate FBX files with unusual structure
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2025-70069 Assimp FBX DoS Attempt"; flow:to_server,established; content:"|4b 61 79 64 61 72 61 20 46 42 58 20 42 69 6e 61 72 79|"; depth:18; content:"|ff ff ff ff|"; distance:0; within:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable FBX Support: If possible, disable the FBX importer in your application until a patch is available.
2. Input Validation: Implement a pre-processing step to validate FBX files before passing them to Assimp. Check for:
   • Material indices within valid range.
   • Properly terminated strings.
   • Correct data structure sizes.
3. Resource Limits: Run Assimp in a sandboxed environment with CPU and memory limits to prevent DoS.

Long-Term Fix:

• Patch: Monitor the Assimp GitHub repository for a security patch. Once released, update to the patched version.
• Alternative Library: Consider switching to a more actively maintained 3D model import library.

Valters IT Signature:

Valters IT
Senior DevSecOps Engineer
Cyber Threat Intelligence Expert

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