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washtml.php
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washtml.php
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<?php
/* Washtml, a HTML sanityzer.
*
* Copyright (c) 2007 Frederic Motte <fmotte@ubixis.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/* Please send me your comments about this code if you have some, thanks, Fred. */
/* OVERVIEW:
*
* Wahstml take an untrusted HTML and return a safe html string.
*
* SYNOPSIS:
*
* $washer = new washtml($config);
* $washer->wash($html);
* It return a sanityzed string of the $html parameter without html and head tags.
* $html is a string containing the html code to wash.
* $config is an array containing options:
* $config['allow_remote'] is a boolean to allow link to remote images.
* $config['blocked_src'] string with image-src to be used for blocked remote images
* $config['show_washed'] is a boolean to include washed out attributes as x-washed
* $config['cid_map'] is an array where cid urls index urls to replace them.
* $config['charset'] is a string containing the charset of the HTML document if it is not defined in it.
* $washer->extlinks is a reference to a boolean that is set to true if remote images were removed. (FE: show remote images link)
*
* INTERNALS:
*
* Only tags and attributes in the static lists $html_elements and $html_attributes
* are kept, inline styles are also filtered: all style identifiers matching
* /[a-z\-]/i are allowed. Values matching colors, sizes, /[a-z\-]/i and safe
* urls if allowed and cid urls if mapped are kept.
*
* BUGS: It MUST be safe !
* - Check regexp
* - urlencode URLs instead of htmlspecials
* - Check is a 3 bytes utf8 first char can eat '">'
* - Update PCRE: CVE-2007-1659 - CVE-2007-1660 - CVE-2007-1661 - CVE-2007-1662
* CVE-2007-4766 - CVE-2007-4767 - CVE-2007-4768
* http://lists.debian.org/debian-security-announce/debian-security-announce-2007/msg00177.html
* - ...
*
* MISSING:
* - relative links, can be implemented by prefixing an absolute path, ask me
* if you need it...
* - ...
*
* Dont be a fool:
* - Dont alter data on a GET: '<img src="http://yourhost/mail?action=delete&uid=3267" />'
* - ...
*
* Roundcube Changes:
* - added $block_elements
* - changed $ignore_elements behaviour
* - added RFC2397 support
* - base URL support
* - invalid HTML comments removal before parsing
*/
class washtml
{
/* Allowed HTML elements (default) */
static $html_elements = array('a', 'abbr', 'acronym', 'address', 'area', 'b', 'basefont', 'bdo', 'big', 'blockquote', 'br', 'caption', 'center', 'cite', 'code', 'col', 'colgroup', 'dd', 'del', 'dfn', 'dir', 'div', 'dl', 'dt', 'em', 'fieldset', 'font', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'hr', 'i', 'ins', 'label', 'legend', 'li', 'map', 'menu', 'nobr', 'ol', 'p', 'pre', 'q', 's', 'samp', 'small', 'span', 'strike', 'strong', 'sub', 'sup', 'table', 'tbody', 'td', 'tfoot', 'th', 'thead', 'tr', 'tt', 'u', 'ul', 'var', 'wbr', 'img');
/* Ignore these HTML tags and their content */
static $ignore_elements = array('script', 'applet', 'embed', 'object', 'style');
/* Allowed HTML attributes */
static $html_attribs = array('name', 'class', 'title', 'alt', 'width', 'height', 'align', 'nowrap', 'col', 'row', 'id', 'rowspan', 'colspan', 'cellspacing', 'cellpadding', 'valign', 'bgcolor', 'color', 'border', 'bordercolorlight', 'bordercolordark', 'face', 'marginwidth', 'marginheight', 'axis', 'border', 'abbr', 'char', 'charoff', 'clear', 'compact', 'coords', 'vspace', 'hspace', 'cellborder', 'size', 'lang', 'dir');
/* Block elements which could be empty but cannot be returned in short form (<tag />) */
static $block_elements = array('div', 'p', 'pre', 'blockquote', 'a', 'font', 'center', 'table', 'ul', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ol', 'dl', 'strong', 'i', 'b');
/* State for linked objects in HTML */
public $extlinks = false;
/* Current settings */
private $config = array();
/* Registered callback functions for tags */
private $handlers = array();
/* Allowed HTML elements */
private $_html_elements = array();
/* Ignore these HTML tags but process their content */
private $_ignore_elements = array();
/* Block elements which could be empty but cannot be returned in short form (<tag />) */
private $_block_elements = array();
/* Allowed HTML attributes */
private $_html_attribs = array();
/* Constructor */
public function __construct($p = array()) {
$this->_html_elements = array_flip((array)$p['html_elements']) + array_flip(self::$html_elements) ;
$this->_html_attribs = array_flip((array)$p['html_attribs']) + array_flip(self::$html_attribs);
$this->_ignore_elements = array_flip((array)$p['ignore_elements']) + array_flip(self::$ignore_elements);
$this->_block_elements = array_flip((array)$p['block_elements']) + array_flip(self::$block_elements);
unset($p['html_elements'], $p['html_attribs'], $p['ignore_elements'], $p['block_elements']);
$this->config = $p + array('show_washed'=>true, 'allow_remote'=>false, 'cid_map'=>array());
}
/* Register a callback function for a certain tag */
public function add_callback($tagName, $callback)
{
$this->handlers[$tagName] = $callback;
}
/* Check CSS style */
private function wash_style($style) {
$s = '';
foreach (explode(';', $style) as $declaration) {
if (preg_match('/^\s*([a-z\-]+)\s*:\s*(.*)\s*$/i', $declaration, $match)) {
$cssid = $match[1];
$str = $match[2];
$value = '';
while (sizeof($str) > 0 &&
preg_match('/^(url\(\s*[\'"]?([^\'"\)]*)[\'"]?\s*\)'./*1,2*/
'|rgb\(\s*[0-9]+\s*,\s*[0-9]+\s*,\s*[0-9]+\s*\)'.
'|-?[0-9.]+\s*(em|ex|px|cm|mm|in|pt|pc|deg|rad|grad|ms|s|hz|khz|%)?'.
'|#[0-9a-f]{3,6}|[a-z0-9\-]+'.
')\s*/i', $str, $match)) {
if ($match[2]) {
if (($src = $this->config['cid_map'][$match[2]])
|| ($src = $this->config['cid_map'][$this->config['base_url'].$match[2]])) {
$value .= ' url('.htmlspecialchars($src, ENT_QUOTES) . ')';
}
else if (preg_match('/^(http|https|ftp):.*$/i', $match[2], $url)) {
if ($this->config['allow_remote'])
$value .= ' url('.htmlspecialchars($url[0], ENT_QUOTES).')';
else
$this->extlinks = true;
}
else if (preg_match('/^data:.+/i', $match[2])) { // RFC2397
$value .= ' url('.htmlspecialchars($match[2], ENT_QUOTES).')';
}
}
else if ($match[0] != 'url' && $match[0] != 'rbg') //whitelist ?
$value .= ' ' . $match[0];
$str = substr($str, strlen($match[0]));
}
if ($value)
$s .= ($s?' ':'') . $cssid . ':' . $value . ';';
}
}
return $s;
}
/* Take a node and return allowed attributes and check values */
private function wash_attribs($node) {
$t = '';
$washed;
foreach ($node->attributes as $key => $plop) {
$key = strtolower($key);
$value = $node->getAttribute($key);
if (isset($this->_html_attribs[$key]) ||
($key == 'href' && preg_match('/^(http:|https:|ftp:|mailto:|#).+/i', $value)))
$t .= ' ' . $key . '="' . htmlspecialchars($value, ENT_QUOTES) . '"';
else if ($key == 'style' && ($style = $this->wash_style($value)))
$t .= ' style="' . $style . '"';
else if ($key == 'background' || ($key == 'src' && strtolower($node->tagName) == 'img')) { //check tagName anyway
if (($src = $this->config['cid_map'][$value])
|| ($src = $this->config['cid_map'][$this->config['base_url'].$value])) {
$t .= ' ' . $key . '="' . htmlspecialchars($src, ENT_QUOTES) . '"';
}
else if (preg_match('/^(http|https|ftp):.+/i', $value)) {
if ($this->config['allow_remote'])
$t .= ' ' . $key . '="' . htmlspecialchars($value, ENT_QUOTES) . '"';
else {
$this->extlinks = true;
if ($this->config['blocked_src'])
$t .= ' ' . $key . '="' . htmlspecialchars($this->config['blocked_src'], ENT_QUOTES) . '"';
}
}
else if (preg_match('/^data:.+/i', $value)) { // RFC2397
$t .= ' ' . $key . '="' . htmlspecialchars($value, ENT_QUOTES) . '"';
}
} else
$washed .= ($washed?' ':'') . $key;
}
return $t . ($washed && $this->config['show_washed']?' x-washed="'.$washed.'"':'');
}
/* The main loop that recurse on a node tree.
* It output only allowed tags with allowed attributes
* and allowed inline styles */
private function dumpHtml($node) {
if(!$node->hasChildNodes())
return '';
$node = $node->firstChild;
$dump = '';
do {
switch($node->nodeType) {
case XML_ELEMENT_NODE: //Check element
$tagName = strtolower($node->tagName);
if ($callback = $this->handlers[$tagName]) {
$dump .= call_user_func($callback, $tagName, $this->wash_attribs($node), $this->dumpHtml($node));
}
else if (isset($this->_html_elements[$tagName])) {
$content = $this->dumpHtml($node);
$dump .= '<' . $tagName . $this->wash_attribs($node) .
// create closing tag for block elements, but also for elements
// with content or with some attributes (eg. style, class) (#1486812)
($content != '' || $node->hasAttributes() || isset($this->_block_elements[$tagName]) ? ">$content</$tagName>" : ' />');
}
else if (isset($this->_ignore_elements[$tagName])) {
$dump .= '<!-- ' . htmlspecialchars($tagName, ENT_QUOTES) . ' not allowed -->';
}
else {
$dump .= '<!-- ' . htmlspecialchars($tagName, ENT_QUOTES) . ' ignored -->';
$dump .= $this->dumpHtml($node); // ignore tags not its content
}
break;
case XML_CDATA_SECTION_NODE:
$dump .= $node->nodeValue;
break;
case XML_TEXT_NODE:
$dump .= htmlspecialchars($node->nodeValue);
break;
case XML_HTML_DOCUMENT_NODE:
$dump .= $this->dumpHtml($node);
break;
case XML_DOCUMENT_TYPE_NODE:
break;
default:
$dump . '<!-- node type ' . $node->nodeType . ' -->';
}
} while($node = $node->nextSibling);
return $dump;
}
/* Main function, give it untrusted HTML, tell it if you allow loading
* remote images and give it a map to convert "cid:" urls. */
public function wash($html)
{
// Charset seems to be ignored (probably if defined in the HTML document)
$node = new DOMDocument('1.0', $this->config['charset']);
$this->extlinks = false;
// Find base URL for images
if (preg_match('/<base\s+href=[\'"]*([^\'"]+)/is', $html, $matches))
$this->config['base_url'] = $matches[1];
else
$this->config['base_url'] = '';
// Remove invalid HTML comments (#1487759)
$html = preg_replace('/<!--[^->]*>/', '', $html);
@$node->loadHTML($html);
return $this->dumpHtml($node);
}
}
?>

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