CVE-2026-10230

Executive Summary

CVE-2026-10230 is a heap-based buffer overflow vulnerability identified in the Assimp library, specifically within the Half-Life 1 MDL Loader component. The flaw resides in the Assimp::MDL::HalfLife::HL1MDLLoader::read_animations function in HL1MDLLoader.cpp. An attacker can exploit this vulnerability by providing a specially crafted Half-Life 1 MDL file, leading to a heap-based buffer overflow. This can cause a denial of service (DoS) or potentially allow arbitrary code execution in the context of the application using the library. The attack vector is local, requiring user interaction to load the malicious file. The vulnerability affects Assimp up to version 6.0.4, and no official patch has been released at this time.

Supply Chain & Package Security

Assimp (Open Asset Import Library) is a widely used library for importing various 3D model formats into applications. It is a critical dependency in many game engines, 3D modeling tools, and rendering software. This vulnerability poses a significant supply chain risk, as any application that uses Assimp to load Half-Life 1 MDL files could be affected. The lack of a patch means that downstream projects must implement their own mitigations or wait for an upstream fix. The exploit is publicly available, increasing the urgency for remediation.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
• Attack Vector (AV): Local (L) - The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) - The attack does not require special conditions.
• Privileges Required (PR): None (N) - No privileges are needed to trigger the vulnerability.
• User Interaction (UI): Required (R) - The victim must load a malicious file.
• Scope (S): Unchanged (U) - The vulnerability does not affect other components.
• Confidentiality (C): None (N) - No data confidentiality impact.
• Integrity (I): None (N) - No data integrity impact.
• Availability (A): High (H) - The vulnerability can cause a complete denial of service.

Threat Level: Medium. The vulnerability requires local access and user interaction, but the exploit is publicly available and can lead to a denial of service. The lack of a patch increases the risk for unpatched systems.

Deep Dive & Mechanics

The vulnerability is a heap-based buffer overflow in the read_animations function of the Half-Life 1 MDL loader. The function reads animation data from a .mdl file and allocates memory on the heap. Due to insufficient bounds checking, an attacker can craft a file with malicious animation data that causes the function to write beyond the allocated buffer.

The root cause is likely an integer overflow or a missing validation of the number of animation frames or their sizes. When the function calculates the required buffer size, it may not properly account for the actual data being read, leading to a heap overflow when copying the animation data.

This type of vulnerability can be exploited to corrupt heap metadata, leading to a crash (DoS) or, in more sophisticated attacks, to arbitrary code execution by overwriting function pointers or other critical data structures.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is the current implementation in Assimp up to version 6.0.4. A hypothetical patch would involve adding proper bounds checking before copying data into the heap buffer.

Vulnerable Code (Conceptual):

void HL1MDLLoader::read_animations() {
    // Read number of animations from file
    int num_anims = read_int();
    // Allocate buffer based on num_anims (vulnerable to integer overflow)
    Animation* anims = new Animation[num_anims];
    for (int i = 0; i < num_anims; i++) {
        // Read animation data directly into buffer without size check
        read_animation_data(&anims[i]);
    }
}

Patched Code (Hypothetical):

void HL1MDLLoader::read_animations() {
    // Read number of animations from file
    int num_anims = read_int();
    // Validate the number of animations to prevent integer overflow
    if (num_anims <= 0 || num_anims > MAX_ANIMATIONS) {
        throw std::runtime_error("Invalid number of animations");
    }
    // Allocate buffer with safe size
    Animation* anims = new (std::nothrow) Animation[num_anims];
    if (!anims) {
        throw std::bad_alloc();
    }
    for (int i = 0; i < num_anims; i++) {
        // Read animation data with bounds checking
        if (!read_animation_data_safe(&anims[i], i)) {
            delete[] anims;
            throw std::runtime_error("Failed to read animation data");
        }
    }
}

Exploitation & Lab Setup

Red Team

Objective: Trigger a heap-based buffer overflow to cause a denial of service or achieve code execution.

Prerequisites:

• A system running an application that uses Assimp (version <= 6.0.4) to load Half-Life 1 MDL files.
• Ability to deliver a malicious .mdl file to the target (e.g., via email, download, or file share).

Steps:

1. Craft a Malicious MDL File: Use a hex editor or a custom script to modify a valid Half-Life 1 MDL file. The exploit targets the animation data section. Increase the number of animations or the size of animation data beyond the allocated buffer.
2. Deliver the File: Send the malicious file to the target user.
3. Trigger the Vulnerability: The user must open the file with an application that uses Assimp (e.g., a 3D model viewer, game engine editor).
4. Observe the Impact: The application may crash (DoS) or exhibit unexpected behavior. For code execution, further heap manipulation is required.

Example Exploit Code (Conceptual):

import struct

def create_malicious_mdl():
    # This is a simplified example; actual MDL format is more complex
    header = b'\x00' * 64  # Placeholder header
    # Set number of animations to a large value to cause overflow
    num_anims = 0x7FFFFFFF
    anim_data = struct.pack('<I', num_anims)
    # Add padding to trigger overflow
    anim_data += b'A' * 0x1000
    return header + anim_data

with open('malicious.mdl', 'wb') as f:
    f.write(create_malicious_mdl())

Blue Team

Objective: Detect and prevent exploitation of CVE-2026-10230.

Detection:

• Monitor for crashes in applications using Assimp when loading MDL files.
• Use file integrity monitoring to detect the presence of suspicious MDL files.
• Implement behavioral analysis to detect heap corruption.

Prevention:

• Sandboxing: Run applications that use Assimp in a sandboxed environment.
• Input Validation: Implement additional validation of MDL files before passing them to Assimp.
• Memory Protection: Use Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP) to mitigate exploitation.
• Update: Monitor for patches from the Assimp project and apply them as soon as available.

Indicators of Compromise (IOCs)

• File Hashes (MD5): e99a18c428cb38d5f260853678922e03 (example, replace with actual)
• File Names: malicious.mdl, exploit.mdl, or any .mdl file from untrusted sources.
• Network Traffic: None (local attack).
• Process Behavior: Application crashes with heap corruption errors (e.g., HEAP CORRUPTION DETECTED in debug builds).
• Registry/File System: Unusual .mdl files in temporary directories or download folders.

Detection Engineering

YARA Rule

rule CVE_2026_10230_Assimp_HL1_MDL_Overflow {
    meta:
        description = "Detects malicious Half-Life 1 MDL files targeting CVE-2026-10230"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-10230"
    strings:
        $mdl_header = "IDST"  // Half-Life MDL magic bytes
        $large_anim_count = { FF FF FF 7F }  // Large animation count (0x7FFFFFFF)
    condition:
        $mdl_header at 0 and $large_anim_count
}

Sigma Rule

title: CVE-2026-10230 - Assimp Half-Life 1 MDL Heap Overflow
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit a heap-based buffer overflow in Assimp via malicious MDL files.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-10230
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\assimp.dll'
        CommandLine|contains: '.mdl'
    condition: selection
falsepositives:
    - Legitimate use of Assimp with valid MDL files
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-10230 - Assimp MDL Heap Overflow Attempt"; flow:to_server; content:"IDST"; offset:0; depth:4; content:"|FF FF FF 7F|"; within:64; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Half-Life 1 MDL Loading: If possible, configure applications using Assimp to not load Half-Life 1 MDL files.
2. Input Validation: Implement a pre-processor that validates MDL files before passing them to Assimp. Check for reasonable animation counts and data sizes.
3. Sandboxing: Run applications that use Assimp in a sandboxed environment with limited privileges.

Long-Term Fix:

• Patch: Await an official patch from the Assimp project. Monitor the project's GitHub repository for updates.
• Upgrade: Once a patched version is released (e.g., > 6.0.4), upgrade immediately.
• Fork: If the project is unresponsive, consider forking the repository and applying a custom patch.

Workarounds:

• Use Alternative Libraries: If feasible, switch to a different 3D model import library that does not have this vulnerability.
• File Scanning: Use antivirus or endpoint detection and response (EDR) solutions to scan for malicious MDL files.

Valters IT
DevSecOps & Cyber Threat Intelligence