File: class.inputfilter.php

<?php

/** @class: InputFilter (PHP4 & PHP5, with comments)
  * @project: PHP Input Filter
  * @date: 10-05-2005
  * @version: 1.2.2_php4/php5
  * @author: Daniel Morris
  * @contributors: Gianpaolo Racca, Ghislain Picard, Marco Wandschneider, Chris Tobin and Andrew Eddie.
  * @copyright: Daniel Morris
  * @email: dan@rootcube.com
  * @license: GNU General Public License (GPL)
  */
class InputFilter {
	var $tagsArray;			// default = empty array
	var $attrArray;			// default = empty array

	var $tagsMethod;		// default = 0
	var $attrMethod;		// default = 0

	var $xssAuto;           // default = 1
	var $tagBlacklist = array('applet', 'body', 'bgsound', 'base', 'basefont', 'embed', 'frame', 'frameset', 'head', 'html', 'id', 'iframe', 'ilayer', 'layer', 'link', 'meta', 'name', 'object', 'script', 'style', 'title', 'xml');
	var $attrBlacklist = array('action', 'background', 'codebase', 'dynsrc', 'lowsrc');  // also will strip ALL event handlers
		
	/** 
	  * Constructor for inputFilter class. Only first parameter is required.
	  * @access constructor
	  * @param Array $tagsArray - list of user-defined tags
	  * @param Array $attrArray - list of user-defined attributes
	  * @param int $tagsMethod - 0= allow just user-defined, 1= allow all but user-defined
	  * @param int $attrMethod - 0= allow just user-defined, 1= allow all but user-defined
	  * @param int $xssAuto - 0= only auto clean essentials, 1= allow clean blacklisted tags/attr
	  */
	function inputFilter($tagsArray = array(), $attrArray = array(), $tagsMethod = 0, $attrMethod = 0, $xssAuto = 1) {		
		// make sure user defined arrays are in lowercase
		for ($i = 0; $i < count($tagsArray); $i++) $tagsArray[$i] = strtolower($tagsArray[$i]);
		for ($i = 0; $i < count($attrArray); $i++) $attrArray[$i] = strtolower($attrArray[$i]);
		// assign to member vars
		$this->tagsArray = (array) $tagsArray;
		$this->attrArray = (array) $attrArray;
		$this->tagsMethod = $tagsMethod;
		$this->attrMethod = $attrMethod;
		$this->xssAuto = $xssAuto;
	}
	
	/** 
	  * Method to be called by another php script. Processes for XSS and specified bad code.
	  * @access public
	  * @param Mixed $source - input string/array-of-string to be 'cleaned'
	  * @return String $source - 'cleaned' version of input parameter
	  */
	function process($source) {
		// clean all elements in this array
		if (is_array($source)) {
			foreach($source as $key => $value)
				// filter element for XSS and other 'bad' code etc.
				if (is_string($value)) $source[$key] = $this->remove($this->decode($value));
			return $source;
		// clean this string
		} else if (is_string($source)) {
			// filter source for XSS and other 'bad' code etc.
			return $this->remove($this->decode($source));
		// return parameter as given
		} else return $source;	
	}

	/** 
	  * Internal method to iteratively remove all unwanted tags and attributes
	  * @access protected
	  * @param String $source - input string to be 'cleaned'
	  * @return String $source - 'cleaned' version of input parameter
	  */
	function remove($source) {
		$loopCounter=0;
		// provides nested-tag protection
		while($source != $this->filterTags($source)) {
			$source = $this->filterTags($source);
			$loopCounter++;
		}
		return $source;
	}	
	
	/** 
	  * Internal method to strip a string of certain tags
	  * @access protected
	  * @param String $source - input string to be 'cleaned'
	  * @return String $source - 'cleaned' version of input parameter
	  */
	function filterTags($source) {
		// filter pass setup
		$preTag = NULL;
		$postTag = $source;
		// find initial tag's position
		$tagOpen_start = strpos($source, '<');
		// interate through string until no tags left
		while($tagOpen_start !== FALSE) {
			// process tag interatively
			$preTag .= substr($postTag, 0, $tagOpen_start);
			$postTag = substr($postTag, $tagOpen_start);
			$fromTagOpen = substr($postTag, 1);
			// end of tag
			$tagOpen_end = strpos($fromTagOpen, '>');
			if ($tagOpen_end === false) break;
			// next start of tag (for nested tag assessment)
			$tagOpen_nested = strpos($fromTagOpen, '<');
			if (($tagOpen_nested !== false) && ($tagOpen_nested < $tagOpen_end)) {
				$preTag .= substr($postTag, 0, ($tagOpen_nested+1));
				$postTag = substr($postTag, ($tagOpen_nested+1));
				$tagOpen_start = strpos($postTag, '<');
				continue;
			} 
			$tagOpen_nested = (strpos($fromTagOpen, '<') + $tagOpen_start + 1);
			$currentTag = substr($fromTagOpen, 0, $tagOpen_end);
			$tagLength = strlen($currentTag);
			if (!$tagOpen_end) {
				$preTag .= $postTag;
				$tagOpen_start = strpos($postTag, '<');			
			}
			// iterate through tag finding attribute pairs - setup
			$tagLeft = $currentTag;
			$attrSet = array();
			$currentSpace = strpos($tagLeft, ' ');
			// is end tag
			if (substr($currentTag, 0, 1) == "/") {
				$isCloseTag = TRUE;
				list($tagName) = explode(' ', $currentTag);
				$tagName = substr($tagName, 1);
			// is start tag
			} else {
				$isCloseTag = FALSE;
				list($tagName) = explode(' ', $currentTag);
			}		
			// excludes all "non-regular" tagnames OR no tagname OR remove if xssauto is on and tag is blacklisted
			if ((!preg_match("/^[a-z][a-z0-9]*$/i",$tagName)) || (!$tagName) || ((in_array(strtolower($tagName), $this->tagBlacklist)) && ($this->xssAuto))) { 				
				$postTag = substr($postTag, ($tagLength + 2));
				$tagOpen_start = strpos($postTag, '<');
				// don't append this tag
				continue;
			}
			// this while is needed to support attribute values with spaces in!
			while ($currentSpace !== FALSE) {
				$fromSpace = substr($tagLeft, ($currentSpace+1));
				$nextSpace = strpos($fromSpace, ' ');
				$openQuotes = strpos($fromSpace, '"');
				$closeQuotes = strpos(substr($fromSpace, ($openQuotes+1)), '"') + $openQuotes + 1;
				// another equals exists
				if (strpos($fromSpace, '=') !== FALSE) {
					// opening and closing quotes exists
					if (($openQuotes !== FALSE) && (strpos(substr($fromSpace, ($openQuotes+1)), '"') !== FALSE))
						$attr = substr($fromSpace, 0, ($closeQuotes+1));
					// one or neither exist
					else $attr = substr($fromSpace, 0, $nextSpace);
				// no more equals exist
				} else $attr = substr($fromSpace, 0, $nextSpace);
				// last attr pair
				if (!$attr) $attr = $fromSpace;
				// add to attribute pairs array
				$attrSet[] = $attr;
				// next inc
				$tagLeft = substr($fromSpace, strlen($attr));
				$currentSpace = strpos($tagLeft, ' ');
			}
			// appears in array specified by user
			$tagFound = in_array(strtolower($tagName), $this->tagsArray);			
			// remove this tag on condition
			if ((!$tagFound && $this->tagsMethod) || ($tagFound && !$this->tagsMethod)) {
				// reconstruct tag with allowed attributes
				if (!$isCloseTag) {
					$attrSet = $this->filterAttr($attrSet);
					$preTag .= '<' . $tagName;
					for ($i = 0; $i < count($attrSet); $i++)
						$preTag .= ' ' . $attrSet[$i];
					// reformat single tags to XHTML
					if (strpos($fromTagOpen, "</" . $tagName)) $preTag .= '>';
					else $preTag .= ' />';
				// just the tagname
			    } else $preTag .= '</' . $tagName . '>';
			}
			// find next tag's start
			$postTag = substr($postTag, ($tagLength + 2));
			$tagOpen_start = strpos($postTag, '<');			
		}
		// append any code after end of tags
		$preTag .= $postTag;
		return $preTag;
	}

	/** 
	  * Internal method to strip a tag of certain attributes
	  * @access protected
	  * @param Array $attrSet
	  * @return Array $newSet
	  */
	function filterAttr($attrSet) {	
		$newSet = array();
		// process attributes
		for ($i = 0; $i <count($attrSet); $i++) {
			// skip blank spaces in tag
			if (!$attrSet[$i]) continue;
			// split into attr name and value
			$attrSubSet = explode('=', trim($attrSet[$i]));
			list($attrSubSet[0]) = explode(' ', $attrSubSet[0]);
			// removes all "non-regular" attr names AND also attr blacklisted
			if ((!eregi("^[a-z]*$",$attrSubSet[0])) || (($this->xssAuto) && ((in_array(strtolower($attrSubSet[0]), $this->attrBlacklist)) || (substr($attrSubSet[0], 0, 2) == 'on')))) 
				continue;
			// xss attr value filtering
			if ($attrSubSet[1]) {
				// strips unicode, hex, etc
				$attrSubSet[1] = str_replace('&#', '', $attrSubSet[1]);
				// strip normal newline within attr value
				$attrSubSet[1] = preg_replace('/\s+/', '', $attrSubSet[1]);
				// strip double quotes
				$attrSubSet[1] = str_replace('"', '', $attrSubSet[1]);
				// [requested feature] convert single quotes from either side to doubles (Single quotes shouldn't be used to pad attr value)
				if ((substr($attrSubSet[1], 0, 1) == "'") && (substr($attrSubSet[1], (strlen($attrSubSet[1]) - 1), 1) == "'"))
					$attrSubSet[1] = substr($attrSubSet[1], 1, (strlen($attrSubSet[1]) - 2));
				// strip slashes
				$attrSubSet[1] = stripslashes($attrSubSet[1]);
			}
			// auto strip attr's with "javascript:
			if (	((strpos(strtolower($attrSubSet[1]), 'expression') !== false) &&	(strtolower($attrSubSet[0]) == 'style')) ||
					(strpos(strtolower($attrSubSet[1]), 'javascript:') !== false) ||
					(strpos(strtolower($attrSubSet[1]), 'behaviour:') !== false) ||
					(strpos(strtolower($attrSubSet[1]), 'vbscript:') !== false) ||
					(strpos(strtolower($attrSubSet[1]), 'mocha:') !== false) ||
					(strpos(strtolower($attrSubSet[1]), 'livescript:') !== false) 
			) continue;

			// if matches user defined array
			$attrFound = in_array(strtolower($attrSubSet[0]), $this->attrArray);
			// keep this attr on condition
			if ((!$attrFound && $this->attrMethod) || ($attrFound && !$this->attrMethod)) {
				// attr has value
				if ($attrSubSet[1]) $newSet[] = $attrSubSet[0] . '="' . $attrSubSet[1] . '"';
				// attr has decimal zero as value
				else if ($attrSubSet[1] == "0") $newSet[] = $attrSubSet[0] . '="0"';
				// reformat single attributes to XHTML
				else $newSet[] = $attrSubSet[0] . '="' . $attrSubSet[0] . '"';
			}	
		}
		return $newSet;
	}
	
	/** 
	  * Try to convert to plaintext
	  * @access protected
	  * @param String $source
	  * @return String $source
	  */
	function decode($source) {
		// url decode
		$source = html_entity_decode($source, ENT_QUOTES, "ISO-8859-1");
		// convert decimal
		$source = preg_replace('/&#(\d+);/me',"chr(\\1)", $source);				// decimal notation
		// convert hex
		$source = preg_replace('/&#x([a-f0-9]+);/mei',"chr(0x\\1)", $source);	// hex notation
		return $source;
	}

	/** 
	  * Method to be called by another php script. Processes for SQL injection
	  * @access public
	  * @param Mixed $source - input string/array-of-string to be 'cleaned'
	  * @param Buffer $connection - An open MySQL connection
	  * @return String $source - 'cleaned' version of input parameter
	  */
	function safeSQL($source, &$connection) {
		// clean all elements in this array
		if (is_array($source)) {
			foreach($source as $key => $value)
				// filter element for SQL injection
				if (is_string($value)) $source[$key] = $this->quoteSmart($this->decode($value), $connection);
			return $source;
		// clean this string
		} else if (is_string($source)) {
			// filter source for SQL injection
			if (is_string($source)) return $this->quoteSmart($this->decode($source), $connection);
		// return parameter as given
		} else return $source;	
	}

	/** 
	  * @author Chris Tobin
	  * @author Daniel Morris
	  * @access protected
	  * @param String $source
	  * @param Resource $connection - An open MySQL connection
	  * @return String $source
	  */
	function quoteSmart($source, &$connection) {
		// strip slashes
		if (get_magic_quotes_gpc()) $source = stripslashes($source);
		// quote both numeric and text
		$source = $this->escapeString($source, $connection);
		return $source;
	}
	
	/** 
	  * @author Chris Tobin
	  * @author Daniel Morris
	  * @access protected
	  * @param String $source
	  * @param Resource $connection - An open MySQL connection
	  * @return String $source
	  */	
	function escapeString($string, &$connection) {
		// depreciated function
		if (version_compare(phpversion(),"4.3.0", "<")) mysql_escape_string($string);
		// current function
		else mysql_real_escape_string($string);
		return $string;
	}
}

?>