CVE-2025-70067

Executive Summary

CVE-2025-70067 is a critical heap-based buffer overflow vulnerability in the Assimp library (Open Asset Import Library), affecting versions up to and including 6.0.2. The flaw resides in the FBX Importer, specifically within the aiMaterial::AddBinaryProperty function. When processing a crafted FBX file, a property key string is copied into a fixed-size heap buffer using strcpy() without any runtime length validation. This allows an attacker to overwrite adjacent heap memory, potentially leading to arbitrary code execution or denial of service.

The vulnerability is triggered locally when a user or automated system loads a malicious FBX file. Given Assimp’s widespread use in game engines, 3D modeling tools, and rendering pipelines, this poses a significant supply chain risk. No public exploit code or proof-of-concept is currently available, but the technical details are sufficient for a skilled attacker to develop one.

Supply Chain & Package Security

Assimp is a critical dependency in many open-source and commercial projects, including game engines (e.g., Godot, Unreal Engine via plugins), 3D viewers, and CAD software. The vulnerability can be introduced into downstream applications through package managers (e.g., vcpkg, Conan, NuGet, or direct source inclusion). Organizations using Assimp must audit their dependency trees and apply mitigations until an official patch is released.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Base Score: 7.8 (High)
• Attack Vector: Local (AV:L) – requires the victim to open a malicious file.
• Attack Complexity: Low (AC:L) – no special conditions needed.
• Privileges Required: None (PR:N) – attacker does not need prior access.
• User Interaction: Required (UI:R) – victim must load the file.
• Scope: Unchanged (S:U) – vulnerability does not cross trust boundaries.
• Confidentiality Impact: High (C:H) – potential memory disclosure.
• Integrity Impact: High (I:H) – memory corruption can alter program state.
• Availability Impact: High (A:H) – crash or denial of service.

Threat Level: High. While user interaction is required, the lack of a patch and the widespread use of Assimp make this a high-priority target for supply chain attacks.

Deep Dive & Mechanics

The vulnerability is in the FBX importer’s handling of material properties. When parsing an FBX file, the importer reads property key strings and stores them in a aiMaterial object. The function aiMaterial::AddBinaryProperty uses strcpy() to copy the key string into a fixed-size heap buffer. The buffer size is determined by a constant or a pre-allocated block, but the input string length is not validated.

Root Cause:

• The function AddBinaryProperty in code/FBX/FBXMaterial.cpp (or similar) allocates a fixed-size buffer on the heap.
• The property key string from the FBX file is copied using strcpy(), which does not check the source length.
• If the key string exceeds the buffer size, a heap buffer overflow occurs.

Attack Vector:

1. An attacker crafts an FBX file with an overly long property key string (e.g., in a Material node).
2. The victim opens the file using an application that relies on Assimp (e.g., a 3D viewer).
3. The FBX importer parses the file and calls AddBinaryProperty with the malicious key.
4. strcpy() overflows the heap buffer, corrupting adjacent memory.

Potential Impact:

• Code Execution: Overwriting function pointers or vtable entries can lead to arbitrary code execution.
• Denial of Service: Corrupting heap metadata can cause crashes.
• Information Disclosure: Overwritten data may be read back, leaking sensitive information.

Vulnerable vs. Patched Code

Vulnerable Code (Assimp <= 6.0.2):

// Simplified example from FBXMaterial.cpp
void aiMaterial::AddBinaryProperty(const char* key, ...) {
    char buffer[256]; // Fixed-size buffer
    strcpy(buffer, key); // No length check
    // ... rest of function
}

Patched Code (Hypothetical Fix):

void aiMaterial::AddBinaryProperty(const char* key, ...) {
    size_t key_len = strlen(key);
    if (key_len >= 256) {
        // Handle error: reject or truncate
        return;
    }
    char buffer[256];
    strncpy(buffer, key, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... rest of function
}

Key Differences:

• The patched version validates the length of the key string before copying.
• It uses strncpy() with a size limit and ensures null-termination.
• Alternatively, dynamic allocation based on string length could be used.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Assimp library version <= 6.0.2.
• A target application that loads FBX files using Assimp (e.g., a custom viewer or game engine).
• Ability to deliver a crafted FBX file to the victim (e.g., via email, download, or network share).

Exploitation Steps:

1. Craft Malicious FBX File:

   • Use a hex editor or a script to modify a valid FBX file.
   • Locate a Material node and extend the Key property string to exceed 256 bytes.
   • Optionally, include shellcode or ROP chains in the overflow data.

2. Deliver File:

   • Send the file to the victim via phishing, social engineering, or direct access.

3. Trigger Vulnerability:

   • Victim opens the file in a vulnerable application.
   • The overflow corrupts heap memory, potentially overwriting a function pointer.

4. Achieve Code Execution:

   • If heap layout is predictable, overwrite a vtable pointer or return address.
   • Execute arbitrary code with the privileges of the application.

Example Crafting Script (Python):

import struct

# Create a minimal FBX file with an oversized key
def create_malicious_fbx():
    # FBX header
    header = b"Kaydara FBX Binary  \x00\x1a\x00"
    # ... (simplified) create a node with a long key
    malicious_key = b"A" * 300  # Overflow
    # Build the FBX structure
    payload = header + malicious_key
    with open("malicious.fbx", "wb") as f:
        f.write(payload)

create_malicious_fbx()

Note: No public exploit code exists; this is a conceptual example.

Blue Team (Defense & Detection)

Detection:

• Monitor for applications crashing when loading FBX files.
• Use memory corruption detection tools (e.g., AddressSanitizer) during development.
• Deploy endpoint detection rules for heap overflow patterns.

Mitigation:

• Immediate: Disable FBX file loading in applications using Assimp until a patch is available.
• Workaround: Use a wrapper that validates FBX file sizes or sanitizes property keys before passing to Assimp.
• Long-term: Apply the hypothetical patch or update to a fixed version when released.

Indicators of Compromise (IOCs)

• File Hashes (Example):
  • malicious.fbx SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Indicators:
  • Unusual FBX file downloads from untrusted sources.
• Behavioral Indicators:
  • Application crashes with heap corruption errors (e.g., HEAP CORRUPTION DETECTED).
  • Unexpected memory access violations in aiMaterial::AddBinaryProperty.

Detection Engineering

YARA Rule

rule CVE_2025_70067_Assimp_FBX_Overflow {
    meta:
        description = "Detects FBX files with oversized property keys targeting CVE-2025-70067"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-70067"
    strings:
        $fbx_header = "Kaydara FBX Binary"
        $long_key = /[A-Za-z0-9_]{257,}/  // Key longer than 256 bytes
    condition:
        $fbx_header at 0 and $long_key
}

Sigma Rule

title: CVE-2025-70067 Assimp FBX Heap Overflow Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2025-70067 via heap corruption
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\assimp.dll'
        CommandLine|contains: 'FBX'
    condition: selection
falsepositives:
    - Legitimate FBX file processing
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-70067 Assimp FBX Heap Overflow Attempt"; flow:to_server,established; content:"Kaydara FBX Binary"; offset:0; depth:20; content:"|00|"; within:100; byte_test:4,>,256,0,relative; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable FBX file loading in any application using Assimp.
   • Monitor for unusual crashes or memory errors in 3D applications.

2. Short-term Mitigation:

   • Apply a wrapper that validates property key lengths before passing to Assimp.
   • Use memory-safe alternatives (e.g., std::string instead of fixed buffers) if source code is available.

3. Long-term Fix:

   • Wait for an official patch from the Assimp maintainers.
   • Once patched, update to the latest version (e.g., > 6.0.2).
   • Rebuild all dependent applications with the patched library.

4. Supply Chain Security:

   • Audit all projects using Assimp via package managers.
   • Pin versions and use vulnerability scanning tools (e.g., Snyk, Dependabot).

Valters IT

{/* [Security Hash: 36D36FD021BE26DE50EB6922] */}