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<?php
class Sanitizer {
public static function rewrite_relative($url, $rel_url) {
$rel_parts = parse_url($rel_url);
if (!empty($rel_parts['host']) && !empty($rel_parts['scheme'])) {
return self::validate($rel_url);
} else if (strpos($rel_url, "//") === 0) {
# protocol-relative URL (rare but they exist)
return self::validate("https:" . $rel_url);
} else if (strpos($rel_url, "magnet:") === 0) {
# allow magnet links
return $rel_url;
} else {
$parts = parse_url($url);
$rel_parts['host'] = $parts['host'];
$rel_parts['scheme'] = $parts['scheme'];
if (isset($rel_parts['path'])) {
if (strpos($rel_parts['path'], '/') !== 0)
$rel_parts['path'] = '/' . $rel_parts['path'];
$rel_parts['path'] = str_replace("/./", "/", $rel_parts['path']);
$rel_parts['path'] = str_replace("//", "/", $rel_parts['path']);
}
return self::validate(self::build_url($rel_parts));
}
}
public static function sanitize($str, $force_remove_images = false) {
$res = trim($str); if (!$res) return '';
$doc = new DOMDocument();
$doc->loadHTML('<?xml encoding="UTF-8">' . $res);
$xpath = new DOMXPath($doc);
// is it a good idea to possibly rewrite urls to our own prefix?
// $rewrite_base_url = $site_url ? $site_url : Config::get_self_url();
$rewrite_base_url = "http://domain.invalid/";
$entries = $xpath->query('(//a[@href]|//img[@src]|//source[@srcset|@src])');
foreach ($entries as $entry) {
if ($entry->hasAttribute('href')) {
$entry->setAttribute('href',
self::rewrite_relative($rewrite_base_url, $entry->getAttribute('href')));
$entry->setAttribute('rel', 'noopener noreferrer');
$entry->setAttribute("target", "_blank");
}
if ($entry->hasAttribute('src')) {
$entry->setAttribute('src',
self::rewrite_relative($rewrite_base_url, $entry->getAttribute('src')));
}
if ($entry->nodeName == 'img') {
$entry->setAttribute('referrerpolicy', 'no-referrer');
$entry->setAttribute('loading', 'lazy');
}
if ($entry->hasAttribute('srcset')) {
$entry->removeAttribute('srcset');
}
}
$allowed_elements = array('a', 'abbr', 'address', 'acronym', 'audio', 'article', 'aside',
'b', 'bdi', 'bdo', 'big', 'blockquote', 'body', 'br',
'caption', 'cite', 'center', 'code', 'col', 'colgroup',
'data', 'dd', 'del', 'details', 'description', 'dfn', 'div', 'dl', 'font',
'dt', 'em', 'footer', 'figure', 'figcaption',
'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'header', 'hr', 'html', 'i',
'img', 'ins', 'kbd', 'li', 'main', 'mark', 'nav', 'noscript',
'ol', 'p', 'picture', 'pre', 'q', 'ruby', 'rp', 'rt', 's', 'samp', 'section',
'small', 'source', 'span', 'strike', 'strong', 'sub', 'summary',
'sup', 'table', 'tbody', 'td', 'tfoot', 'th', 'thead', 'time',
'tr', 'track', 'tt', 'u', 'ul', 'var', 'wbr', 'video', 'xml:namespace' );
$disallowed_attributes = array('id', 'style', 'class', 'width', 'height', 'allow');
$doc->removeChild($doc->firstChild); //remove doctype
$doc = self::strip_harmful_tags($doc, $allowed_elements, $disallowed_attributes);
$res = $doc->saveHTML();
/* strip everything outside of <body>...</body> */
$res_frag = array();
if (preg_match('/<body>(.*)<\/body>/is', $res, $res_frag)) {
return $res_frag[1];
} else {
return $res;
}
}
private static function strip_harmful_tags($doc, $allowed_elements, $disallowed_attributes) {
$xpath = new DOMXPath($doc);
$entries = $xpath->query('//*');
foreach ($entries as $entry) {
if (!in_array($entry->nodeName, $allowed_elements)) {
$entry->parentNode->removeChild($entry);
}
if ($entry->hasAttributes()) {
$attrs_to_remove = array();
foreach ($entry->attributes as $attr) {
if (strpos($attr->nodeName, 'on') === 0) {
array_push($attrs_to_remove, $attr);
}
if (strpos($attr->nodeName, "data-") === 0) {
array_push($attrs_to_remove, $attr);
}
if ($attr->nodeName == 'href' && stripos($attr->value, 'javascript:') === 0) {
array_push($attrs_to_remove, $attr);
}
if (in_array($attr->nodeName, $disallowed_attributes)) {
array_push($attrs_to_remove, $attr);
}
}
foreach ($attrs_to_remove as $attr) {
$entry->removeAttributeNode($attr);
}
}
}
return $doc;
}
// extended filtering involves validation for safe ports and loopback
static function validate($url, $extended_filtering = false) {
$url = trim($url);
# fix protocol-relative URLs
if (strpos($url, "//") === 0)
$url = "https:" . $url;
$tokens = parse_url($url);
// this isn't really necessary because filter_var(... FILTER_VALIDATE_URL) requires host and scheme
// as per https://php.watch/versions/7.3/filter-var-flag-deprecation but it might save time
if (empty($tokens['host']))
return false;
if (!in_array(strtolower($tokens['scheme']), ['http', 'https']))
return false;
//convert IDNA hostname to punycode if possible
if (function_exists("idn_to_ascii")) {
if (mb_detect_encoding($tokens['host']) != 'ASCII') {
if (defined('IDNA_NONTRANSITIONAL_TO_ASCII') && defined('INTL_IDNA_VARIANT_UTS46')) {
$tokens['host'] = idn_to_ascii($tokens['host'], IDNA_NONTRANSITIONAL_TO_ASCII, INTL_IDNA_VARIANT_UTS46);
} else {
$tokens['host'] = idn_to_ascii($tokens['host']);
}
}
}
// separate set of tokens with urlencoded 'path' because filter_var() rightfully fails on non-latin characters
// (used for validation only, we actually request the original URL, in case of urlencode breaking it)
$tokens_filter_var = $tokens;
if ($tokens['path'] ?? false) {
$tokens_filter_var['path'] = implode("/",
array_map("rawurlencode",
array_map("rawurldecode",
explode("/", $tokens['path']))));
}
$url = self::build_url($tokens);
$url_filter_var = self::build_url($tokens_filter_var);
if (filter_var($url_filter_var, FILTER_VALIDATE_URL) === false)
return false;
if ($extended_filtering) {
if (!in_array($tokens['port'] ?? '', [80, 443, '']))
return false;
if (strtolower($tokens['host']) == 'localhost' || $tokens['host'] == '::1' || strpos($tokens['host'], '127.') === 0)
return false;
}
return $url;
}
static function build_url($parts) {
$tmp = $parts['scheme'] . "://" . $parts['host'];
if (isset($parts['path'])) $tmp .= $parts['path'];
if (isset($parts['query'])) $tmp .= '?' . $parts['query'];
if (isset($parts['fragment'])) $tmp .= '#' . $parts['fragment'];
return $tmp;
}
static function resolve_redirects($url, $timeout, $nest = 0) {
// too many redirects
if ($nest > 10)
return false;
if (version_compare(PHP_VERSION, '7.1.0', '>=')) {
$context_options = array(
'http' => array(
'header' => array(
'Connection: close'
),
'method' => 'HEAD',
'timeout' => $timeout,
'protocol_version'=> 1.1)
);
$context = stream_context_create($context_options);
$headers = get_headers($url, 0, $context);
} else {
$headers = get_headers($url, 0);
}
if (is_array($headers)) {
$headers = array_reverse($headers); // last one is the correct one
foreach($headers as $header) {
if (stripos($header, 'Location:') === 0) {
$url = self::rewrite_relative($url, trim(substr($header, strlen('Location:'))));
return self::resolve_redirects($url, $timeout, $nest + 1);
}
}
return $url;
}
// request failed?
return false;
}
}
|
