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5f7cd735ea
Case would be blocked by CSP but adding for cases where CSP may not be active when content taken externally. For #3636
107 lines
3.7 KiB
PHP
107 lines
3.7 KiB
PHP
<?php
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namespace BookStack\Util;
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use DOMAttr;
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use DOMDocument;
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use DOMElement;
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use DOMNodeList;
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use DOMXPath;
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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.
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*/
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public static function removeScripts(string $html): string
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{
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if (empty($html)) {
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return $html;
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}
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$html = '<body>' . $html . '</body>';
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libxml_use_internal_errors(true);
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$doc = new DOMDocument();
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$doc->loadHTML(mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8'));
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$xPath = new DOMXPath($doc);
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// Remove standard script tags
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$scriptElems = $xPath->query('//script');
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static::removeNodes($scriptElems);
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// Remove clickable links to JavaScript URI
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$badLinks = $xPath->query('//*[' . static::xpathContains('@href', 'javascript:') . ']');
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static::removeNodes($badLinks);
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// Remove forms with calls to JavaScript URI
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$badForms = $xPath->query('//*[' . static::xpathContains('@action', 'javascript:') . '] | //*[' . static::xpathContains('@formaction', 'javascript:') . ']');
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static::removeNodes($badForms);
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// Remove meta tag to prevent external redirects
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$metaTags = $xPath->query('//meta[' . static::xpathContains('@content', 'url') . ']');
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static::removeNodes($metaTags);
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// Remove data or JavaScript iFrames
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$badIframes = $xPath->query('//*[' . static::xpathContains('@src', 'data:') . '] | //*[' . static::xpathContains('@src', 'javascript:') . '] | //*[@srcdoc]');
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static::removeNodes($badIframes);
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// Remove tags hiding JavaScript or data uris in values attribute.
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// For example, SVG animate tag can exploit javascript in values.
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$badValuesTags = $xPath->query('//*[' . static::xpathContains('@values', 'data:') . '] | //*[' . static::xpathContains('@values', 'javascript:') . ']');
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static::removeNodes($badValuesTags);
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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 = $xPath->query('//@*[contains(name(), \'xlink:href\')]');
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static::removeAttributes($xlinkHrefAttributes);
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// Remove 'on*' attributes
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$onAttributes = $xPath->query('//@*[starts-with(name(), \'on\')]');
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static::removeAttributes($onAttributes);
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$html = '';
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$topElems = $doc->documentElement->childNodes->item(0)->childNodes;
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foreach ($topElems as $child) {
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$html .= $doc->saveHTML($child);
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}
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return $html;
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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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