103 lines
3.6 KiB
PHP
103 lines
3.6 KiB
PHP
<?php
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namespace BookStack\Util;
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use DOMAttr;
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use DOMElement;
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use DOMNodeList;
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class HtmlContentFilter
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{
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/**
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* Remove all the script elements from the given HTML document.
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*/
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public static function removeScriptsFromDocument(HtmlDocument $doc)
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{
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// Remove standard script tags
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$scriptElems = $doc->queryXPath('//script');
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static::removeNodes($scriptElems);
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// Remove clickable links to JavaScript URI
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$badLinks = $doc->queryXPath('//*[' . static::xpathContains('@href', 'javascript:') . ']');
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static::removeNodes($badLinks);
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// Remove forms with calls to JavaScript URI
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$badForms = $doc->queryXPath('//*[' . static::xpathContains('@action', 'javascript:') . '] | //*[' . static::xpathContains('@formaction', 'javascript:') . ']');
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static::removeNodes($badForms);
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// Remove meta tag to prevent external redirects
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$metaTags = $doc->queryXPath('//meta[' . static::xpathContains('@content', 'url') . ']');
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static::removeNodes($metaTags);
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// Remove data or JavaScript iFrames
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$badIframes = $doc->queryXPath('//*[' . static::xpathContains('@src', 'data:') . '] | //*[' . static::xpathContains('@src', 'javascript:') . '] | //*[@srcdoc]');
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static::removeNodes($badIframes);
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// Remove attributes, within svg children, hiding JavaScript or data uris.
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// A bunch of svg element and attribute combinations expose xss possibilities.
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// For example, SVG animate tag can exploit javascript in values.
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$badValuesAttrs = $doc->queryXPath('//svg//@*[' . static::xpathContains('.', 'data:') . '] | //svg//@*[' . static::xpathContains('.', 'javascript:') . ']');
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static::removeAttributes($badValuesAttrs);
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// Remove elements with a xlink:href attribute
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// Used in SVG but deprecated anyway, so we'll be a bit more heavy-handed here.
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$xlinkHrefAttributes = $doc->queryXPath('//@*[contains(name(), \'xlink:href\')]');
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static::removeAttributes($xlinkHrefAttributes);
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// Remove 'on*' attributes
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$onAttributes = $doc->queryXPath('//@*[starts-with(name(), \'on\')]');
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static::removeAttributes($onAttributes);
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}
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/**
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* Remove scripts from the given HTML string.
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*/
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public static function removeScriptsFromHtmlString(string $html): string
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{
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if (empty($html)) {
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return $html;
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}
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$doc = new HtmlDocument($html);
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static::removeScriptsFromDocument($doc);
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return $doc->getBodyInnerHtml();
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}
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/**
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* Create a xpath contains statement with a translation automatically built within
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* to affectively search in a cases-insensitive manner.
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*/
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protected static function xpathContains(string $property, string $value): string
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{
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$value = strtolower($value);
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$upperVal = strtoupper($value);
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return 'contains(translate(' . $property . ', \'' . $upperVal . '\', \'' . $value . '\'), \'' . $value . '\')';
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}
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/**
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* Remove all the given DOMNodes.
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*/
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protected static function removeNodes(DOMNodeList $nodes): void
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{
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foreach ($nodes as $node) {
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$node->parentNode->removeChild($node);
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}
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}
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/**
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* Remove all the given attribute nodes.
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*/
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protected static function removeAttributes(DOMNodeList $attrs): void
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{
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/** @var DOMAttr $attr */
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foreach ($attrs as $attr) {
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$attrName = $attr->nodeName;
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/** @var DOMElement $parentNode */
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$parentNode = $attr->parentNode;
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$parentNode->removeAttribute($attrName);
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}
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}
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}
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