LykanShield protection layer

MimeType Filter

Trust file contents, not the MIME type claimed by the browser.

Read integration guide View source on GitHub →

Overview

Server-side content identification

The filter reads the temporary upload with PHP Fileinfo and compares the detected MIME type with the current LykanShield allowlist. Client-provided MIME metadata is retained only for diagnostics and never drives the security decision.

Request lifecycle

How it works

  1. 01

    Read safely

    LykanShield verifies that the temporary upload exists and is readable.

  2. 02

    Detect MIME

    finfo with FILEINFO_MIME_TYPE identifies the content on the server.

  3. 03

    Apply allowlist

    Unknown or disallowed types are blocked and recorded as MIME_FILE_UPLOAD.

Implementation

Technical details

  • Requires the PHP Fileinfo extension.
  • Normalizes detected and configured MIME values to lowercase.
  • Supports monitor or block behavior when the remote allowlist is unavailable.
  • Reports both the detected type and the client claim for investigation.

Relevant configuration

<?php
lykan_config::$config['filter_active']['mime_types'] = true;
lykan_config::$config['rules_unavailable_action'] = 'monitor';
require __DIR__ . '/includes/lykan.class.php';
lykan::run(__DIR__);