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<?php /** * htmlfilter.inc * --------------- * This set of functions allows you to filter html in order to remove * any malicious tags from it. Useful in cases when you need to filter * user input for any cross-site-scripting attempts. * * Copyright (C) 2002-2004 by Duke University * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA * * @Author Konstantin Riabitsev <icon@linux.duke.edu> * @Version 1.1 ($Date: 2011-07-04 14:02:23 -0400 (Mon, 04 Jul 2011) $) */ /** * @Author Jim Jagielski <jim@jaguNET.com / jimjag@gmail.com> */ /** * This function returns the final tag out of the tag name, an array * of attributes, and the type of the tag. This function is called by * tln_sanitize internally. * * @param $tagname the name of the tag. * @param $attary the array of attributes and their values * @param $tagtype The type of the tag (see in comments). * @return a string with the final tag representation. */ function tln_tagprint($tagname, $attary, $tagtype){ $me = 'tln_tagprint'; if ($tagtype == 2){ $fulltag = '</' . $tagname . '>'; } else { $fulltag = '<' . $tagname; if (is_array($attary) && sizeof($attary)){ $atts = Array(); while (list($attname, $attvalue) = each($attary)){ array_push($atts, "$attname=$attvalue"); } $fulltag .= ' ' . join(' ', $atts); } if ($tagtype == 3){ $fulltag .= ' /'; } $fulltag .= '>'; } return $fulltag; } /** * A small helper function to use with array_walk. Modifies a by-ref * value and makes it lowercase. * * @param $val a value passed by-ref. * @return void since it modifies a by-ref value. */ function tln_casenormalize(&$val){ $val = strtolower($val); } /** * This function skips any whitespace from the current position within * a string and to the next non-whitespace value. * * @param $body the string * @param $offset the offset within the string where we should start * looking for the next non-whitespace character. * @return the location within the $body where the next * non-whitespace char is located. */ function tln_skipspace($body, $offset){ $me = 'tln_skipspace'; preg_match('/^(\s*)/s', substr($body, $offset), $matches); if (sizeof($matches[1])){ $count = strlen($matches[1]); $offset += $count; } return $offset; } /** * This function looks for the next character within a string. It's * really just a glorified "strpos", except it catches the failures * nicely. * * @param $body The string to look for needle in. * @param $offset Start looking from this position. * @param $needle The character/string to look for. * @return location of the next occurance of the needle, or * strlen($body) if needle wasn't found. */ function tln_findnxstr($body, $offset, $needle){ $me = 'tln_findnxstr'; $pos = strpos($body, $needle, $offset); if ($pos === FALSE){ $pos = strlen($body); } return $pos; } /** * This function takes a PCRE-style regexp and tries to match it * within the string. * * @param $body The string to look for needle in. * @param $offset Start looking from here. * @param $reg A PCRE-style regex to match. * @return Returns a false if no matches found, or an array * with the following members: * - integer with the location of the match within $body * - string with whatever content between offset and the match * - string with whatever it is we matched */ function tln_findnxreg($body, $offset, $reg){ $me = 'tln_findnxreg'; $matches = Array(); $retarr = Array(); $preg_rule = '%^(.*?)(' . $reg . ')%s'; preg_match($preg_rule, substr($body, $offset), $matches); if (!isset($matches[0])){ $retarr = false; } else { $retarr[0] = $offset + strlen($matches[1]); $retarr[1] = $matches[1]; $retarr[2] = $matches[2]; } return $retarr; } /** * This function looks for the next tag. * * @param $body String where to look for the next tag. * @param $offset Start looking from here. * @return false if no more tags exist in the body, or * an array with the following members: * - string with the name of the tag * - array with attributes and their values * - integer with tag type (1, 2, or 3) * - integer where the tag starts (starting "<") * - integer where the tag ends (ending ">") * first three members will be false, if the tag is invalid. */ function tln_getnxtag($body, $offset){ $me = 'tln_getnxtag'; if ($offset > strlen($body)){ return false; } $lt = tln_findnxstr($body, $offset, '<'); if ($lt == strlen($body)){ return false; } /** * We are here: * blah blah <tag attribute="value"> * \---------^ */ $pos = tln_skipspace($body, $lt + 1); if ($pos >= strlen($body)){ return Array(false, false, false, $lt, strlen($body)); } /** * There are 3 kinds of tags: * 1. Opening tag, e.g.: * <a href="blah"> * 2. Closing tag, e.g.: * </a> * 3. XHTML-style content-less tag, e.g.: * <img src="blah"/> */ $tagtype = false; switch (substr($body, $pos, 1)){ case '/': $tagtype = 2; $pos++; break; case '!': /** * A comment or an SGML declaration. */ if (substr($body, $pos+1, 2) == '--'){ $gt = strpos($body, '-->', $pos); if ($gt === false){ $gt = strlen($body); } else { $gt += 2; } return Array(false, false, false, $lt, $gt); } else { $gt = tln_findnxstr($body, $pos, '>'); return Array(false, false, false, $lt, $gt); } break; default: /** * Assume tagtype 1 for now. If it's type 3, we'll switch values * later. */ $tagtype = 1; break; } $tag_start = $pos; $tagname = ''; /** * Look for next [\W-_], which will indicate the end of the tag name. */ $regary = tln_findnxreg($body, $pos, '[^\w\-_]'); if ($regary == false){ return Array(false, false, false, $lt, strlen($body)); } list($pos, $tagname, $match) = $regary; $tagname = strtolower($tagname); /** * $match can be either of these: * '>' indicating the end of the tag entirely. * '\s' indicating the end of the tag name. * '/' indicating that this is type-3 xhtml tag. * * Whatever else we find there indicates an invalid tag. */ switch ($match){ case '/': /** * This is an xhtml-style tag with a closing / at the * end, like so: <img src="blah"/>. Check if it's followed * by the closing bracket. If not, then this tag is invalid */ if (substr($body, $pos, 2) == '/>'){ $pos++; $tagtype = 3; } else { $gt = tln_findnxstr($body, $pos, '>'); $retary = Array(false, false, false, $lt, $gt); return $retary; } case '>': return Array($tagname, false, $tagtype, $lt, $pos); break; default: /** * Check if it's whitespace */ if (preg_match('/\s/', $match)){ } else { /** * This is an invalid tag! Look for the next closing ">". */ $gt = tln_findnxstr($body, $lt, '>'); return Array(false, false, false, $lt, $gt); } } /** * At this point we're here: * <tagname attribute='blah'> * \-------^ * * At this point we loop in order to find all attributes. */ $attname = ''; $atttype = false; $attary = Array(); while ($pos <= strlen($body)){ $pos = tln_skipspace($body, $pos); if ($pos == strlen($body)){ /** * Non-closed tag. */ return Array(false, false, false, $lt, $pos); } /** * See if we arrived at a ">" or "/>", which means that we reached * the end of the tag. */ $matches = Array(); preg_match('%^(\s*)(>|/>)%s', substr($body, $pos), $matches); if (isset($matches[0]) && $matches[0]){ /** * Yep. So we did. */ $pos += strlen($matches[1]); if ($matches[2] == '/>'){ $tagtype = 3; $pos++; } return Array($tagname, $attary, $tagtype, $lt, $pos); } /** * There are several types of attributes, with optional * [:space:] between members. * Type 1: * attrname[:space:]=[:space:]'CDATA' * Type 2: * attrname[:space:]=[:space:]"CDATA" * Type 3: * attr[:space:]=[:space:]CDATA * Type 4: * attrname * * We leave types 1 and 2 the same, type 3 we check for * '"' and convert to """ if needed, then wrap in * double quotes. Type 4 we convert into: * attrname="yes". */ $regary = tln_findnxreg($body, $pos, '[^\w\-_]'); if ($regary == false){ /** * Looks like body ended before the end of tag. */ return Array(false, false, false, $lt, strlen($body)); } list($pos, $attname, $match) = $regary; $attname = strtolower($attname); /** * We arrived at the end of attribute name. Several things possible * here: * '>' means the end of the tag and this is attribute type 4 * '/' if followed by '>' means the same thing as above * '\s' means a lot of things -- look what it's followed by. * anything else means the attribute is invalid. */ switch($match){ case '/': /** * This is an xhtml-style tag with a closing / at the * end, like so: <img src="blah"/>. Check if it's followed * by the closing bracket. If not, then this tag is invalid */ if (substr($body, $pos, 2) == '/>'){ $pos++; $tagtype = 3; } else { $gt = tln_findnxstr($body, $pos, '>'); $retary = Array(false, false, false, $lt, $gt); return $retary; } case '>': $attary{$attname} = '"yes"'; return Array($tagname, $attary, $tagtype, $lt, $pos); break; default: /** * Skip whitespace and see what we arrive at. */ $pos = tln_skipspace($body, $pos); $char = substr($body, $pos, 1); /** * Two things are valid here: * '=' means this is attribute type 1 2 or 3. * \w means this was attribute type 4. * anything else we ignore and re-loop. End of tag and * invalid stuff will be caught by our checks at the beginning * of the loop. */ if ($char == '='){ $pos++; $pos = tln_skipspace($body, $pos); /** * Here are 3 possibilities: * "'" attribute type 1 * '"' attribute type 2 * everything else is the content of tag type 3 */ $quot = substr($body, $pos, 1); if ($quot == '\''){ $regary = tln_findnxreg($body, $pos+1, '\''); if ($regary == false){ return Array(false, false, false, $lt, strlen($body)); } list($pos, $attval, $match) = $regary; $pos++; $attary{$attname} = '\'' . $attval . '\''; } else if ($quot == '"'){ $regary = tln_findnxreg($body, $pos+1, '\"'); if ($regary == false){ return Array(false, false, false, $lt, strlen($body)); } list($pos, $attval, $match) = $regary; $pos++; $attary{$attname} = '"' . $attval . '"'; } else { /** * These are hateful. Look for \s, or >. */ $regary = tln_findnxreg($body, $pos, '[\s>]'); if ($regary == false){ return Array(false, false, false, $lt, strlen($body)); } list($pos, $attval, $match) = $regary; /** * If it's ">" it will be caught at the top. */ $attval = preg_replace('/\"/s', '"', $attval); $attary{$attname} = '"' . $attval . '"'; } } else if (preg_match('|[\w/>]|', $char)) { /** * That was attribute type 4. */ $attary{$attname} = '"yes"'; } else { /** * An illegal character. Find next '>' and return. */ $gt = tln_findnxstr($body, $pos, '>'); return Array(false, false, false, $lt, $gt); } } } /** * The fact that we got here indicates that the tag end was never * found. Return invalid tag indication so it gets stripped. */ return Array(false, false, false, $lt, strlen($body)); } /** * Translates entities into literal values so they can be checked. * * @param $attvalue the by-ref value to check. * @param $regex the regular expression to check against. * @param $hex whether the entites are hexadecimal. * @return True or False depending on whether there were matches. */ function tln_deent(&$attvalue, $regex, $hex=false){ $me = 'tln_deent'; $ret_match = false; preg_match_all($regex, $attvalue, $matches); if (is_array($matches) && sizeof($matches[0]) > 0){ $repl = Array(); for ($i = 0; $i < sizeof($matches[0]); $i++){ $numval = $matches[1][$i]; if ($hex){ $numval = hexdec($numval); } $repl{$matches[0][$i]} = chr($numval); } $attvalue = strtr($attvalue, $repl); return true; } else { return false; } } /** * This function checks attribute values for entity-encoded values * and returns them translated into 8-bit strings so we can run * checks on them. * * @param $attvalue A string to run entity check against. * @return Nothing, modifies a reference value. */ function tln_defang(&$attvalue){ $me = 'tln_defang'; /** * Skip this if there aren't ampersands or backslashes. */ if (strpos($attvalue, '&') === false && strpos($attvalue, '\\') === false){ return; } $m = false; do { $m = false; $m = $m || tln_deent($attvalue, '/\�*(\d+);*/s'); $m = $m || tln_deent($attvalue, '/\�*((\d|[a-f])+);*/si', true); $m = $m || tln_deent($attvalue, '/\\\\(\d+)/s', true); } while ($m == true); $attvalue = stripslashes($attvalue); } /** * Kill any tabs, newlines, or carriage returns. Our friends the * makers of the browser with 95% market value decided that it'd * be funny to make "java[tab]script" be just as good as "javascript". * * @param attvalue The attribute value before extraneous spaces removed. * @return attvalue Nothing, modifies a reference value. */ function tln_unspace(&$attvalue){ $me = 'tln_unspace'; if (strcspn($attvalue, "\t\r\n\0 ") != strlen($attvalue)){ $attvalue = str_replace(Array("\t", "\r", "\n", "\0", " "), Array('', '', '', '', ''), $attvalue); } } /** * This function runs various checks against the attributes. * * @param $tagname String with the name of the tag. * @param $attary Array with all tag attributes. * @param $rm_attnames See description for tln_sanitize * @param $bad_attvals See description for tln_sanitize * @param $add_attr_to_tag See description for tln_sanitize * @return Array with modified attributes. */ function tln_fixatts($tagname, $attary, $rm_attnames, $bad_attvals, $add_attr_to_tag ){ $me = 'tln_fixatts'; while (list($attname, $attvalue) = each($attary)){ /** * See if this attribute should be removed. */ foreach ($rm_attnames as $matchtag=>$matchattrs){ if (preg_match($matchtag, $tagname)){ foreach ($matchattrs as $matchattr){ if (preg_match($matchattr, $attname)){ unset($attary{$attname}); continue; } } } } /** * Remove any backslashes, entities, or extraneous whitespace. */ tln_defang($attvalue); tln_unspace($attvalue); /** * Now let's run checks on the attvalues. * I don't expect anyone to comprehend this. If you do, * get in touch with me so I can drive to where you live and * shake your hand personally. :) */ foreach ($bad_attvals as $matchtag=>$matchattrs){ if (preg_match($matchtag, $tagname)){ foreach ($matchattrs as $matchattr=>$valary){ if (preg_match($matchattr, $attname)){ /** * There are two arrays in valary. * First is matches. * Second one is replacements */ list($valmatch, $valrepl) = $valary; $newvalue = preg_replace($valmatch,$valrepl,$attvalue); if ($newvalue != $attvalue){ $attary{$attname} = $newvalue; } } } } } } /** * See if we need to append any attributes to this tag. */ foreach ($add_attr_to_tag as $matchtag=>$addattary){ if (preg_match($matchtag, $tagname)){ $attary = array_merge($attary, $addattary); } } return $attary; } /** * * @param $body the string with HTML you wish to filter * @param $tag_list see description above * @param $rm_tags_with_content see description above * @param $self_closing_tags see description above * @param $force_tag_closing see description above * @param $rm_attnames see description above * @param $bad_attvals see description above * @param $add_attr_to_tag see description above * @return tln_sanitized html safe to show on your pages. */ function tln_sanitize($body, $tag_list, $rm_tags_with_content, $self_closing_tags, $force_tag_closing, $rm_attnames, $bad_attvals, $add_attr_to_tag ) { $me = 'tln_sanitize'; /** * Normalize rm_tags and rm_tags_with_content. */ $rm_tags = array_shift($tag_list); @array_walk($tag_list, 'tln_casenormalize'); @array_walk($rm_tags_with_content, 'tln_casenormalize'); @array_walk($self_closing_tags, 'tln_casenormalize'); /** * See if tag_list is of tags to remove or tags to allow. * false means remove these tags * true means allow these tags */ $curpos = 0; $open_tags = Array(); $trusted = "<!-- begin tln_sanitized html -->\n"; $skip_content = false; /** * Take care of netscape's stupid javascript entities like * &{alert('boo')}; */ $body = preg_replace('/&(\{.*?\};)/si', '&\\1', $body); while (($curtag = tln_getnxtag($body, $curpos)) != FALSE){ list($tagname, $attary, $tagtype, $lt, $gt) = $curtag; $free_content = substr($body, $curpos, $lt - $curpos); if ($skip_content == false){ $trusted .= $free_content; } else { } if ($tagname != FALSE){ if ($tagtype == 2){ if ($skip_content == $tagname){ /** * Got to the end of tag we needed to remove. */ $tagname = false; $skip_content = false; } else { if ($skip_content == false){ if (isset($open_tags{$tagname}) && $open_tags{$tagname} > 0){ $open_tags{$tagname}--; } else { $tagname = false; } } else { } } } else { /** * $rm_tags_with_content */ if ($skip_content == false){ /** * See if this is a self-closing type and change * tagtype appropriately. */ if ($tagtype == 1 && in_array($tagname, $self_closing_tags)){ $tagtype = 3; } /** * See if we should skip this tag and any content * inside it. */ if ($tagtype == 1 && in_array($tagname, $rm_tags_with_content)){ $skip_content = $tagname; } else { if (($rm_tags == false && in_array($tagname, $tag_list)) || ($rm_tags == true && !in_array($tagname, $tag_list))){ $tagname = false; } else { if ($tagtype == 1){ if (isset($open_tags{$tagname})){ $open_tags{$tagname}++; } else { $open_tags{$tagname} = 1; } } /** * This is where we run other checks. */ if (is_array($attary) && sizeof($attary) > 0){ $attary = tln_fixatts($tagname, $attary, $rm_attnames, $bad_attvals, $add_attr_to_tag); } } } } else { } } if ($tagname != false && $skip_content == false){ $trusted .= tln_tagprint($tagname, $attary, $tagtype); } } else { } $curpos = $gt + 1; } $trusted .= substr($body, $curpos, strlen($body) - $curpos); if ($force_tag_closing == true){ foreach ($open_tags as $tagname=>$opentimes){ while ($opentimes > 0){ $trusted .= '</' . $tagname . '>'; $opentimes--; } } $trusted .= "\n"; } $trusted .= "<!-- end tln_sanitized html -->\n"; return $trusted; } // // Use the nifty htmlfilter library // function HTMLFilter($body, $trans_image_path, $block_external_images = false) { $tag_list = Array( false, "object", "meta", "html", "head", "base", "link", "frame", "iframe", "plaintext", "marquee" ); $rm_tags_with_content = Array( "script", "applet", "embed", "title", "frameset", "xmp", "xml" ); $self_closing_tags = Array( "img", "br", "hr", "input", "outbind" ); $force_tag_closing = true; $rm_attnames = Array( "/.*/" => Array( // "/target/i", "/^on.*/i", "/^dynsrc/i", "/^data.*/i", "/^lowsrc.*/i" ) ); $bad_attvals = Array( "/.*/" => Array( "/^src|background/i" => Array( Array( "/^([\'\"])\s*\S+script\s*:.*([\'\"])/si", "/^([\'\"])\s*mocha\s*:*.*([\'\"])/si", "/^([\'\"])\s*about\s*:.*([\'\"])/si" ), Array( "\\1$trans_image_path\\2", "\\1$trans_image_path\\2", "\\1$trans_image_path\\2", "\\1$trans_image_path\\2" ) ), "/^href|action/i" => Array( Array( "/^([\'\"])\s*\S+script\s*:.*([\'\"])/si", "/^([\'\"])\s*mocha\s*:*.*([\'\"])/si", "/^([\'\"])\s*about\s*:.*([\'\"])/si" ), Array( "\\1#\\1", "\\1#\\1", "\\1#\\1", "\\1#\\1" ) ), "/^style/i" => Array( Array( "/expression/i", "/binding/i", "/behaviou*r/i", "/include-source/i", "/position\s*:\s*absolute/i", "/url\s*\(\s*([\'\"])\s*\S+script\s*:.*([\'\"])\s*\)/si", "/url\s*\(\s*([\'\"])\s*mocha\s*:.*([\'\"])\s*\)/si", "/url\s*\(\s*([\'\"])\s*about\s*:.*([\'\"])\s*\)/si", "/(.*)\s*:\s*url\s*\(\s*([\'\"]*)\s*\S+script\s*:.*([\'\"]*)\s*\)/si" ), Array( "idiocy", "idiocy", "idiocy", "idiocy", "", "url(\\1#\\1)", "url(\\1#\\1)", "url(\\1#\\1)", "url(\\1#\\1)", "url(\\1#\\1)", "\\1:url(\\2#\\3)" ) ) ) ); if ($block_external_images){ array_push($bad_attvals{'/.*/'}{'/^src|background/i'}[0], '/^([\'\"])\s*https*:.*([\'\"])/si'); array_push($bad_attvals{'/.*/'}{'/^src|background/i'}[1], "\\1$trans_image_path\\1"); array_push($bad_attvals{'/.*/'}{'/^style/i'}[0], '/url\(([\'\"])\s*https*:.*([\'\"])\)/si'); array_push($bad_attvals{'/.*/'}{'/^style/i'}[1], "url(\\1$trans_image_path\\1)"); } $add_attr_to_tag = Array( "/^a$/i" => Array('target'=>'"_blank"') ); $trusted = tln_sanitize($body, $tag_list, $rm_tags_with_content, $self_closing_tags, $force_tag_closing, $rm_attnames, $bad_attvals, $add_attr_to_tag ); return $trusted; } ?>