SVGBlacklistPreProcessor.php

Go to the documentation of this file.

<?php
 
namespace ILIAS\FileUpload\Processor;
 
use ILIAS\FileUpload\DTO\Metadata;
use ILIAS\Filesystem\Stream\FileStream;
use ILIAS\FileUpload\DTO\ProcessingStatus;
 
final class SVGBlacklistPreProcessor implements PreProcessor
{
    use IsMimeTypeOrExtension;
 
    private const SVG_MIME_TYPE = 'image/svg+xml';
    private const REGEX_SCRIPT = '/<script/m';
    private const REGEX_BASE64 = '/data:.*;base64/m';
    private const SVG = 'svg';
    private $rejection_message = 'The SVG file contains possibily malicious code.';
    private $ok_message = 'SVG OK';
    private $svg_event_lists = [
        "onbegin",
        "onend",
        "onrepeat",
        "onabort",
        "onerror",
        "onresize",
        "onscroll",
        "onunload",
        "onabort",
        "onerror",
        "onresize",
        "onscroll",
        "onunload",
        "oncancel",
        "oncanplay",
        "oncanplaythrough",
        "onchange",
        "onclick",
        "onclose",
        "oncuechange",
        "ondblclick",
        "ondrag",
        "ondragend",
        "ondragenter",
        "ondragleave",
        "ondragover",
        "ondragstart",
        "ondrop",
        "ondurationchange",
        "onemptied",
        "onended",
        "onerror",
        "onfocus",
        "oninput",
        "oninvalid",
        "onkeydown",
        "onkeypress",
        "onkeyup",
        "onload",
        "onloadeddata",
        "onloadedmetadata",
        "onloadstart",
        "onmousedown",
        "onmouseenter",
        "onmouseleave",
        "onmousemove",
        "onmouseout",
        "onmouseover",
        "onmouseup",
        "onmousewheel",
        "onpause",
        "onplay",
        "onplaying",
        "onprogress",
        "onratechange",
        "onreset",
        "onresize",
        "onscroll",
        "onseeked",
        "onseeking",
        "onselect",
        "onshow",
        "onstalled",
        "onsubmit",
        "onsuspend",
        "ontimeupdate",
        "ontoggle",
        "onvolumechange",
        "onwaiting",
        "onactivate",
        "onfocusin",
        "onfocusout"
    ];
 
    public function __construct(?string $rejection_message = null)
    {
        $this->rejection_message = $rejection_message ?? $this->rejection_message;
    }
 
    private function isSVG(Metadata $metadata) : bool
    {
        return $this->isMimeTypeOrExtension(
            $metadata,
            self::SVG,
            [self::SVG_MIME_TYPE]
        );
    }
 
    public function process(FileStream $stream, Metadata $metadata) : ProcessingStatus
    {
        if ($this->isSVG($metadata) && !$this->checkStream($stream)) {
            return new ProcessingStatus(ProcessingStatus::DENIED, $this->rejection_message);
        }
        return new ProcessingStatus(ProcessingStatus::OK, $this->ok_message);
    }
 
    public function getDomDocument(string $raw_svg_content) : ?\DOMDocument
    {
        $dom = new \DOMDocument();
        try {
            $dom->loadXML($raw_svg_content, LIBXML_NOWARNING | LIBXML_NOERROR);
        } catch (\Exception $e) {
            return null;
        }
        $errors = libxml_get_errors();
        if ($errors !== []) {
            return null;
        }
        return $dom;
    }
 
    protected function checkStream(FileStream $stream) : bool
    {
        $raw_svg_content = (string) $stream;
        if (false === $raw_svg_content) {
            return false;
        }
 
        // Check for script tags directly
        if ($this->hasContentScriptTag($raw_svg_content)) {
            return false;
        }
 
        // Analyze the SVG
        $dom = $this->getDomDocument($raw_svg_content);
        if ($dom === null) {
            return false;
        }
 
        // loop through all attributes of elements recursively and check for event attributes
        $looper = $this->getDOMAttributesLooper();
        $prohibited_attributes = function (string $name) : bool {
            return in_array(strtolower($name), $this->svg_event_lists, true);
        };
        if ($looper($dom, $prohibited_attributes) === false) {
            return false;
        }
 
        return true;
    }
 
    private function hasContentScriptTag(string $raw_svg_content) : bool
    {
        // Check for Base64 encoded Content
        if (preg_match(self::REGEX_BASE64, $raw_svg_content)) {
            $this->rejection_message = $this->rejection_message
                . ' (base64).';
            return true;
        }
 
        // Check for script tags directly
        if (preg_match(self::REGEX_SCRIPT, $raw_svg_content)) {
            $this->rejection_message = $this->rejection_message
                . ' (script).';
            return true;
        }
 
        return false;
    }
 
    protected function getDOMAttributesLooper() : \Closure
    {
        return function (\DOMDocument $dom, \Closure $closure) : bool {
            $attributes_looper = function (\DOMNode $node, \Closure $closure) use (&$attributes_looper) : bool {
                foreach ($node->attributes as $attribute) {
                    if ($closure($attribute->name)) {
                        $this->rejection_message = sprintf(
                            'The SVG file contains malicious code. (%s).',
                            $attribute->name
                        );
                        return false;
                    }
                }
                foreach ($node->childNodes as $child) {
                    if ($child instanceof \DOMElement) {
                        $attributes_looper($child, $closure);
                    }
                }
                return true;
            };
            foreach ($dom->getElementsByTagName("*") as $i => $element) {
                if ($attributes_looper($element, $closure) === false) {
                    return false;
                }
            }
            return true;
        };
    }
}