CVE-2024-48425

Executive Summary

CVE-2024-48425 is a denial-of-service vulnerability in the Assimp library, specifically in the Assimp::SplitLargeMeshesProcess_Triangle::UpdateNode function. During fuzz testing with AddressSanitizer, a segmentation fault (SEGV) was triggered due to a null pointer dereference. The crash occurs when the code attempts to read from memory address 0x000000000460, which is on the zero page, indicating an invalid pointer access. This vulnerability can be exploited by providing a crafted 3D model file (e.g., OBJ, FBX, or COLLADA) that causes the library to crash, leading to a denial of service in applications that use Assimp for asset import. No public exploit code or proof-of-concept is available, and the vendor has not released a patch.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector (AV): Network (likely, as crafted files can be delivered remotely)
• Attack Complexity (AC): Low (no special conditions required)
• Privileges Required (PR): None
• User Interaction (UI): Required (victim must open the malicious file)
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High (crash leads to denial of service)
• Threat Level: Medium (denial of service only, no code execution)

Deep Dive & Mechanics

The vulnerability resides in the SplitLargeMeshesProcess_Triangle::UpdateNode function within the Assimp library. This function is part of the post-processing pipeline that splits large meshes into smaller ones to improve rendering performance. The crash occurs when the function attempts to dereference a pointer that has not been properly initialized or has been corrupted.

During fuzz testing, a crafted input file caused the function to access memory at address 0x000000000460, which is in the zero page (typically unmapped). This indicates a null pointer dereference or an out-of-bounds read from a null-like pointer. The root cause is likely a missing null check on a node pointer or an array index that becomes negative or too large, leading to an invalid memory access.

The vulnerability is triggered during the import of a 3D model file. The attacker can craft a file that, when parsed, creates a malformed scene graph where a node has an invalid parent or child pointer. The UpdateNode function then tries to traverse this graph and crashes.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the SplitLargeMeshesProcess_Triangle::UpdateNode function. A hypothetical fix would involve adding null pointer checks before dereferencing node pointers and validating array indices.

Vulnerable code (pseudocode):

void SplitLargeMeshesProcess_Triangle::UpdateNode(aiNode* node) {
    // No null check on node
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        UpdateNode(node->mChildren[i]); // Could be null
    }
    // Process mesh data...
}

Patched code (hypothetical):

void SplitLargeMeshesProcess_Triangle::UpdateNode(aiNode* node) {
    if (node == nullptr) return; // Added null check
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        if (node->mChildren[i] != nullptr) {
            UpdateNode(node->mChildren[i]);
        }
    }
    // Process mesh data...
}

Exploitation & Lab Setup

Red Team

No public exploit code is available. To reproduce the crash, an attacker would need to craft a malformed 3D model file (e.g., OBJ, FBX, or COLLADA) that triggers the null pointer dereference. This can be done by fuzzing the Assimp library with a tool like AFL++ or libFuzzer.

Lab Setup:

1. Install Assimp (v5.2.5 or earlier) on a Linux system.
2. Compile with AddressSanitizer: cmake -DCMAKE_CXX_FLAGS="-fsanitize=address -g" ..
3. Create a fuzzing harness that calls Assimp::Importer::ReadFile().
4. Use a fuzzer to generate inputs that cause the crash.
5. The crash will manifest as a SEGV with AddressSanitizer output.

Blue Team

Detection of exploitation attempts relies on monitoring for crashes in applications that use Assimp. Since no code execution is possible, the primary risk is denial of service.

Detection Steps:

• Monitor application logs for segmentation faults or crashes when processing 3D model files.
• Use AddressSanitizer in development environments to catch null pointer dereferences.
• Implement input validation for 3D model files before passing them to Assimp.

Indicators of Compromise (IOCs)

• File Hashes: No specific hashes available; any crafted 3D model file that triggers the crash.
• Process Behavior: Application crash (segmentation fault) when importing a 3D model file.
• Memory Access: Read access violation at address 0x000000000460.
• Error Logs: AddressSanitizer output indicating a heap-buffer-overflow or null pointer dereference in Assimp::SplitLargeMeshesProcess_Triangle::UpdateNode.

Detection Engineering

YARA Rule

rule CVE_2024_48425_Assimp_Null_Deref {
    meta:
        description = "Detects crafted 3D model files that may trigger CVE-2024-48425 in Assimp"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $magic_ob = { 4F 42 4A } // OBJ magic bytes
        $magic_fbx = { 46 42 58 } // FBX magic bytes
        $crash_pattern = { 00 00 00 00 00 00 04 60 } // Address 0x460 in little-endian
    condition:
        ($magic_ob or $magic_fbx) and $crash_pattern
}

Sigma Rule

title: Assimp Null Pointer Dereference Crash
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects crashes in Assimp library due to null pointer dereference (CVE-2024-48425)
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: assimp
detection:
    selection:
        EventID: 1000 (Application Error)
        Application: "assimp*"
        ExceptionCode: 0xc0000005 (Access Violation)
        FaultAddress: "0x000000000460"
    condition: selection
falsepositives:
    - Unknown
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-48425 Assimp Null Pointer Dereference"; flow:to_server; content:"|4F 42 4A|"; depth:3; content:"|00 00 00 00 00 00 04 60|"; distance:0; within:8; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable the SplitLargeMeshesProcess post-processing step if not required. This can be done by not passing the aiProcess_SplitLargeMeshes flag to Assimp::Importer::ReadFile().
• Short-term: Implement input validation for 3D model files. Use a sandbox or separate process to handle file imports to contain crashes.
• Long-term: Apply a patch from the vendor when available. Monitor the Assimp GitHub repository for updates.
• Workaround: Use an alternative library for 3D model parsing until a fix is released.

Valters IT
DevSecOps & Cyber Threat Intelligence