FileSanitizer

Pure PHP file sanitizer and scanner for uploaded files. It strips metadata where practical, rewrites selected file types into safer forms, and detects suspicious or malicious content such as XSS-style payloads, risky embedded markup, active PDF content, and dangerous archive entries.

Features

• Re-encodes supported image formats to remove metadata and ancillary chunks
• Sanitizes HTML and SVG using strict policy-based cleanup
• Scans PDFs for active content and applies best-effort cleanup
• Scans OOXML documents for risky content such as macros, ActiveX, and external relationships
• Recursively scans ZIP archives, including nested archives, with configurable safety limits
• Scans audio files for suspicious embedded payloads and removes metadata where practical
• Scans video files for suspicious embedded payloads and applies best-effort metadata cleanup
• Supports sanitize-always mode for best-effort cleaning even when risky content is detected
• Pure PHP implementation with no shell access, SSH, or external binaries required

Installation

composer require sytxlabs/filesanitizer

For development and tests:

composer install
composer test

Quick start

<?php

require __DIR__ . '/vendor/autoload.php';

use SytxLabs\FileSanitizer\FileSanitizer;

$sanitizer = new FileSanitizer();

$result = $sanitizer->process(__DIR__ . '/upload.svg');

if (!$result['scan']->safe) {
    foreach ($result['scan']->issues as $issue) {
        echo $issue->code . ': ' . $issue->message . PHP_EOL;
    }

    exit(1);
}

echo 'Sanitized file written to: ' . $result['sanitize']->outputPath . PHP_EOL;

sanitizeAlways mode

When sanitizeAlways is enabled, FileSanitizer will attempt best-effort sanitization even if risky content is detected during scanning.

This is useful when you want to:

• always strip metadata where possible
• always rewrite supported files where possible
• keep findings for review without immediately rejecting the upload

<?php

use SytxLabs\FileSanitizer\FileSanitizer;

$sanitizer = new FileSanitizer();

$result = $sanitizer->process(__DIR__ . '/upload.pdf', null, true);

Best-effort sanitization does not guarantee a full structural rebuild for complex formats such as PDF, audio, or video containers.

Supported file types

FileSanitizer currently supports scanning and/or sanitizing the following file types.

• Images
  • JPEG
  • PNG
  • GIF
  • WebP
• Documents and markup
  • HTML
  • SVG
  • PDF
  • TXT and text-like files
  • DOCX
  • XLSX
  • PPTX
• Archives
  • ZIP
  • Nested ZIP archives
• Audio
  • MP3
  • WAV
  • OGG
  • FLAC
  • M4A
  • AAC
• Video
  • MP4
  • MOV
  • WebM
  • MKV
  • AVI

How it works

FileSanitizer combines format-aware scanning with best-effort sanitization.

Scanning

The scanner looks for suspicious patterns and risky structures such as:

• inline JavaScript-style payloads
• dangerous HTML or SVG constructs
• active PDF actions
• suspicious archive paths and nested archive abuse
• risky embedded strings in audio and video containers
• macros, ActiveX, and external relationships in OOXML files

Sanitizing

Supported sanitizers attempt to reduce risk by:

• re-encoding images
• removing unsafe HTML and SVG elements and attributes
• stripping metadata where practical
• rewriting selected file formats into safer forms
• applying best-effort cleanup to complex containers

Archive scanning

ZIP scanning is recursive and designed to detect suspicious content without using shell extraction.

Current guards:

• maximum nesting depth: 3
• maximum scanned entries per archive: 1000
• maximum expanded bytes scanned: 25 MB
• suspicious path detection for entries such as ../evil.txt or absolute paths

HTML and SVG policy

HTML and SVG sanitization is policy-based and removes risky constructs instead of relying on simple tag stripping.

Highlights:

• removes script, iframe, object, embed, form, and other disallowed elements
• removes all on* event handlers
• removes javascript:, vbscript:, file:, and unsafe data: URLs
• removes hostile CSS such as expression(), @import, url(), behavior:, and -moz-binding
• removes SVG active content such as script, foreignObject, animation elements, external media, image, and use

Audio support

FileSanitizer includes best-effort support for common audio formats.

What it does

• Detects suspicious embedded payloads such as:

  • <script
  • javascript:
  • inline event handler patterns like onclick=
  • <iframe
  • data:text/html
  • embedded PHP tags

• Removes metadata where practical:

  • MP3: ID3v1 and ID3v2 tags
  • WAV: selected metadata chunks such as LIST, INFO, and ID3
  • OGG, FLAC, M4A, and AAC: conservative best-effort textual payload cleanup

Notes

Audio sanitization is best-effort and does not transcode or fully rebuild complex media containers. No shell tools, SSH access, or external binaries are required.

Video support

FileSanitizer includes best-effort support for common video containers.

What it does

• Detects suspicious embedded payloads such as:

  • <script
  • javascript:
  • inline event handler patterns like onload=
  • <iframe
  • data:text/html
  • embedded PHP tags

• Applies conservative container cleanup where practical:

  • MP4 and MOV: attempts to remove selected metadata atoms such as udta, meta, and ilst
  • AVI: removes selected metadata chunks such as INFO, JUNK, and IDIT
  • WebM and MKV: applies conservative best-effort textual payload cleanup

Notes

Video sanitization is best-effort and does not transcode or fully rebuild media containers. Without external tools such as FFmpeg, full structural video rewriting is intentionally out of scope.

Test coverage

Included PHPUnit coverage exercises:

• nested ZIP detection
• path traversal detection inside ZIPs
• HTML sanitization rules
• SVG sanitization rules
• PDF action detection
• audio metadata stripping
• video file scanning for embedded payloads and metadata stripping

Limitations

FileSanitizer is a pure PHP package focused on safe, practical, best-effort sanitization.

Important limitations

• PDF sanitization is a best-effort and not a full PDF rebuild
• OOXML files are scanned for risky content but are not fully rewritten
• audio sanitization removes metadata where practical but does not transcode files
• video sanitization is best-effort and does not perform full re-encoding or container rebuilding
• complex media formats may still require deeper inspection in high-security environments