CVE-2025-70071

Executive Summary

CVE-2025-70071 is a denial-of-service (DoS) vulnerability in the Assimp library version 6.0.2, specifically within the FBXParser.cpp file's ParseVectorDataArray() function. An unauthenticated 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 5.9 (Medium) and currently has no known patch or public exploit code. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the risk remains for systems processing untrusted FBX files.

CVSS Breakdown & Threat Level

• CVSS Score: 5.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector: Network (AV:N) – The attacker can send the malicious file remotely.
• 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 interact.
• 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 service becomes unavailable.

Threat Level: Medium. While the impact is limited to availability, the low attack complexity and network vector make it a viable vector for disrupting services that process FBX files.

Deep Dive & Mechanics

The vulnerability resides in the ParseVectorDataArray() function within FBXParser.cpp. This function is responsible for parsing vector data arrays from FBX files. The issue likely stems from improper handling of malformed or excessively large input data, leading to a null pointer dereference or an out-of-bounds memory access. When the parser encounters a crafted FBX file with unexpected vector data, it may attempt to access memory beyond allocated bounds or dereference a null pointer, causing a segmentation fault and crashing the application.

The root cause is a lack of input validation on the size or structure of the vector data array. An attacker can craft an FBX file that specifies an invalid array length or contains data that triggers an infinite loop or memory exhaustion, resulting in a denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (Assimp v6.0.2):

// FBXParser.cpp (simplified)
void ParseVectorDataArray(FBXNode &node) {
    // No bounds checking on array size
    int size = node.GetIntProperty("Size");
    float *data = new float[size * 3];
    for (int i = 0; i < size; i++) {
        data[i * 3] = node.GetFloatProperty("X");
        data[i * 3 + 1] = node.GetFloatProperty("Y");
        data[i * 3 + 2] = node.GetFloatProperty("Z");
    }
    // ... use data
}

Patched Code (Hypothetical Fix):

// FBXParser.cpp (patched)
void ParseVectorDataArray(FBXNode &node) {
    int size = node.GetIntProperty("Size");
    // Validate size to prevent excessive allocation
    if (size <= 0 || size > MAX_VECTOR_ARRAY_SIZE) {
        throw std::runtime_error("Invalid vector array size");
    }
    float *data = new (std::nothrow) float[size * 3];
    if (!data) {
        throw std::bad_alloc();
    }
    for (int i = 0; i < size; i++) {
        data[i * 3] = node.GetFloatProperty("X");
        data[i * 3 + 1] = node.GetFloatProperty("Y");
        data[i * 3 + 2] = node.GetFloatProperty("Z");
    }
    // ... use data
}

The patched version adds input validation for the array size and uses std::nothrow to handle allocation failures gracefully.

Exploitation & Lab Setup

Red Team

Objective: Cause a denial of service on a system using Assimp to parse FBX files.

Lab Setup:

1. Environment: Ubuntu 22.04 LTS with Assimp v6.0.2 installed.
2. Target Application: A simple C++ program that loads an FBX file using Assimp.
3. Exploit File: A crafted FBX file with a malformed vector data array.

Steps:

1. Create a malicious FBX file using a hex editor or a script. The file should contain a VectorData property with an extremely large Size value (e.g., 999999999) or a negative value.
2. Transfer the file to the target system.
3. Run the target application with the malicious FBX file as input.
4. Observe the application crash due to memory exhaustion or segmentation fault.

Example Crafted FBX Snippet:

; FBX 7.4.0 project file
; ...
NodeAttribute: "VectorData", "Vector3" {
    Properties70:  {
        P: "Size", "int", "", "", 999999999
        P: "X", "float", "", "", 1.0
        P: "Y", "float", "", "", 2.0
        P: "Z", "float", "", "", 3.0
    }
}

Blue Team

Detection:

• Monitor for crashes or abnormal terminations of applications using Assimp.
• Use file integrity monitoring to detect unexpected FBX files.
• Implement network monitoring for FBX file transfers.

Mitigation:

• Isolate systems that process FBX files from untrusted sources.
• Use a sandbox or container to run the parsing application.
• Apply input validation and sanitization on FBX files before processing.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example – replace with actual if available)
  • e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (malicious FBX)
• Network Patterns: FBX file transfers from untrusted IPs.
• System Logs: Segmentation faults or out-of-memory errors in application logs.
• Process Behavior: Application crash with signal SIGSEGV or SIGABRT.

Detection Engineering

YARA Rule

rule CVE_2025_70071_Assimp_FBX_DoS {
    meta:
        description = "Detects malicious FBX files exploiting CVE-2025-70071"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-70071"
    strings:
        $fbx_header = "FBX"
        $vector_data = "VectorData"
        $large_size = /Size.*[0-9]{7,}/  // Size value with 7+ digits
    condition:
        $fbx_header at 0 and $vector_data and $large_size
}

Sigma Rule

title: CVE-2025-70071 Assimp FBX DoS Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2025-70071 via malicious FBX files
author: Valters IT
date: 2025-04-10
logsource:
    category: file_event
    product: windows
detection:
    selection:
        EventID: 11  # FileCreate
        TargetFilename|endswith: '.fbx'
        TargetFilename|contains: 'malicious'
    condition: selection
falsepositives:
    - Legitimate large FBX files
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-70071 Assimp FBX DoS Attempt"; flow:to_server; content:"FBX"; content:"VectorData"; content:"Size"; distance:0; within:100; pcre:"/Size.*[0-9]{7,}/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable processing of FBX files from untrusted sources.
   • Use a web application firewall (WAF) to filter FBX file uploads.
   • Monitor for crashes and block IPs sending malicious files.

2. Long-term Fix:

   • Apply input validation in ParseVectorDataArray() to limit array size.
   • Use safe memory allocation practices (e.g., std::nothrow).
   • Update to a patched version of Assimp when available.

3. Workarounds:

   • Use an alternative library for FBX parsing.
   • Pre-process FBX files with a validator before feeding to Assimp.

Valters IT
Securing Digital Frontiers

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