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# kses 0.2.1 - HTML/XHTML filter that only allows some elements and attributes
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# Copyright (C) 2002, 2003 Ulf Harnhammar
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# This program is free software and open source software; you can redistribute
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# it and/or modify it under the terms of the GNU General Public License as
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# published by the Free Software Foundation; either version 2 of the License,
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# or (at your option) any later version.
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# This program is distributed in the hope that it will be useful, but WITHOUT
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# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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# You should have received a copy of the GNU General Public License along
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# with this program; if not, write to the Free Software Foundation, Inc.,
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# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA or visit
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# http://www.gnu.org/licenses/gpl.html
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# *** CONTACT INFORMATION ***
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# E-mail: metaur at users dot sourceforge dot net
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# Web page: http://sourceforge.net/projects/kses
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# Paper mail: (not at the moment)
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# [kses strips evil scripts!]
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function kses($string, $allowed_html, $allowed_protocols =
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array('http', 'https', 'ftp', 'news', 'nntp', 'telnet',
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###############################################################################
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# This function makes sure that only the allowed HTML element names, attribute
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# names and attribute values plus only sane HTML entities will occur in
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# $string. You have to remove any slashes from PHP's magic quotes before you
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###############################################################################
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$string = kses_no_null($string);
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$string = kses_js_entities($string);
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$string = kses_normalize_entities($string);
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$string = kses_hook($string);
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$allowed_html_fixed = kses_array_lc($allowed_html);
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return kses_split($string, $allowed_html_fixed, $allowed_protocols);
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function kses_hook($string)
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###############################################################################
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# You add any kses hooks here.
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###############################################################################
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} # function kses_hook
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function kses_version()
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###############################################################################
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# This function returns kses' version number.
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###############################################################################
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} # function kses_version
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function kses_split($string, $allowed_html, $allowed_protocols)
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###############################################################################
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# This function searches for HTML tags, no matter how malformed. It also
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# matches stray ">" characters.
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###############################################################################
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return preg_replace('%(<'. # EITHER: <
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'[^>]*'. # things that aren't >
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'(>|$)'. # > or end of string
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'|>)%e', # OR: just a >
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"kses_split2('\\1', \$allowed_html, ".
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'$allowed_protocols)',
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} # function kses_split
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function kses_split2($string, $allowed_html, $allowed_protocols)
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###############################################################################
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# This function does a lot of work. It rejects some very malformed things
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# like <:::>. It returns an empty string, if the element isn't allowed (look
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# ma, no strip_tags()!). Otherwise it splits the tag into an element and an
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###############################################################################
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$string = kses_stripslashes($string);
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if (substr($string, 0, 1) != '<')
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# It matched a ">" character
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if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $string, $matches))
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# It's seriously malformed
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$slash = trim($matches[1]);
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$attrlist = $matches[3];
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if ( !is_array($allowed_html[strtolower($elem)]))
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# They are using a not allowed HTML element
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return kses_attr("$slash$elem", $attrlist, $allowed_html,
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} # function kses_split2
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function kses_attr($element, $attr, $allowed_html, $allowed_protocols)
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###############################################################################
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# This function removes all attributes, if none are allowed for this element.
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# If some are allowed it calls kses_hair() to split them further, and then it
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# builds up new HTML code from the data that kses_hair() returns. It also
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# removes "<" and ">" characters, if there are any left. One more thing it
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# does is to check if the tag has a closing XHTML slash, and if it does,
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# it puts one in the returned code as well.
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###############################################################################
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# Is there a closing XHTML slash at the end of the attributes?
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if (preg_match('%\s/\s*$%', $attr))
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# Are any attributes allowed at all for this element?
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if (count($allowed_html[strtolower($element)]) == 0)
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return "<$element$xhtml_slash>";
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$attrarr = kses_hair($attr, $allowed_protocols);
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# Go through $attrarr, and save the allowed attributes for this element
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foreach ($attrarr as $arreach)
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$current = $allowed_html[strtolower($element)]
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[strtolower($arreach['name'])];
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continue; # the attribute is not allowed
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if (!is_array($current))
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$attr2 .= ' '.$arreach['whole'];
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# there are no checks
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# there are some checks
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foreach ($current as $currkey => $currval)
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if (!kses_check_attr_val($arreach['value'], $arreach['vless'],
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{ $ok = false; break; }
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$attr2 .= ' '.$arreach['whole']; # it passed them
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} # if !is_array($current)
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# Remove any "<" or ">" characters
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$attr2 = preg_replace('/[<>]/', '', $attr2);
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return "<$element$attr2$xhtml_slash>";
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} # function kses_attr
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function kses_hair($attr, $allowed_protocols)
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###############################################################################
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# This function does a lot of work. It parses an attribute list into an array
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# with attribute data, and tries to do the right thing even if it gets weird
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# input. It will add quotes around attribute values that don't have any quotes
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# or apostrophes around them, to make it easier to produce HTML code that will
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# conform to W3C's HTML specification. It will also remove bad URL protocols
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# from attribute values.
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###############################################################################
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# Loop through the whole attribute list
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while (strlen($attr) != 0)
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$working = 0; # Was the last operation successful?
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case 0: # attribute name, href for instance
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if (preg_match('/^([-a-zA-Z]+)/', $attr, $match))
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$attrname = $match[1];
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$working = $mode = 1;
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$attr = preg_replace('/^[-a-zA-Z]+/', '', $attr);
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case 1: # equals sign or valueless ("selected")
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if (preg_match('/^\s*=\s*/', $attr)) # equals sign
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$working = 1; $mode = 2;
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$attr = preg_replace('/^\s*=\s*/', '', $attr);
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if (preg_match('/^\s+/', $attr)) # valueless
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$working = 1; $mode = 0;
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('name' => $attrname,
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'whole' => $attrname,
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$attr = preg_replace('/^\s+/', '', $attr);
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case 2: # attribute value, a URL after href= for instance
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if (preg_match('/^"([^"]*)"(\s+|$)/', $attr, $match))
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$thisval = kses_bad_protocol($match[1], $allowed_protocols);
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('name' => $attrname,
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'whole' => "$attrname=\"$thisval\"",
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$working = 1; $mode = 0;
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$attr = preg_replace('/^"[^"]*"(\s+|$)/', '', $attr);
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if (preg_match("/^'([^']*)'(\s+|$)/", $attr, $match))
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$thisval = kses_bad_protocol($match[1], $allowed_protocols);
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('name' => $attrname,
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'whole' => "$attrname='$thisval'",
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$working = 1; $mode = 0;
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$attr = preg_replace("/^'[^']*'(\s+|$)/", '', $attr);
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if (preg_match("%^([^\s\"']+)(\s+|$)%", $attr, $match))
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$thisval = kses_bad_protocol($match[1], $allowed_protocols);
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('name' => $attrname,
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'whole' => "$attrname=\"$thisval\"",
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# We add quotes to conform to W3C's HTML spec.
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$working = 1; $mode = 0;
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$attr = preg_replace("%^[^\s\"']+(\s+|$)%", '', $attr);
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if ($working == 0) # not well formed, remove and try again
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$attr = kses_html_error($attr);
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# special case, for when the attribute list ends with a valueless
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# attribute like "selected"
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('name' => $attrname,
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'whole' => $attrname,
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} # function kses_hair
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function kses_check_attr_val($value, $vless, $checkname, $checkvalue)
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###############################################################################
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# This function performs different checks for attribute values. The currently
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# implemented checks are "maxlen", "minlen", "maxval", "minval" and "valueless"
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# with even more checks to come soon.
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###############################################################################
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switch (strtolower($checkname))
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# The maxlen check makes sure that the attribute value has a length not
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# greater than the given value. This can be used to avoid Buffer Overflows
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# in WWW clients and various Internet servers.
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if (strlen($value) > $checkvalue)
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# The minlen check makes sure that the attribute value has a length not
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# smaller than the given value.
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if (strlen($value) < $checkvalue)
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# The maxval check does two things: it checks that the attribute value is
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# an integer from 0 and up, without an excessive amount of zeroes or
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# whitespace (to avoid Buffer Overflows). It also checks that the attribute
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# value is not greater than the given value.
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# This check can be used to avoid Denial of Service attacks.
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if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
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if ($value > $checkvalue)
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# The minval check checks that the attribute value is a positive integer,
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# and that it is not smaller than the given value.
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if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
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if ($value < $checkvalue)
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# The valueless check checks if the attribute has a value
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# (like <a href="blah">) or not (<option selected>). If the given value
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# is a "y" or a "Y", the attribute must not have a value.
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# If the given value is an "n" or an "N", the attribute must have one.
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if (strtolower($checkvalue) != $vless)
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} # function kses_check_attr_val
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function kses_bad_protocol($string, $allowed_protocols)
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###############################################################################
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# This function removes all non-allowed protocols from the beginning of
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# $string. It ignores whitespace and the case of the letters, and it does
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# understand HTML entities. It does its work in a while loop, so it won't be
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# fooled by a string like "javascript:javascript:alert(57)".
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###############################################################################
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$string = kses_no_null($string);
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$string2 = $string.'a';
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while ($string != $string2)
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$string = kses_bad_protocol_once($string, $allowed_protocols);
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} # function kses_bad_protocol
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function kses_no_null($string)
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###############################################################################
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# This function removes any NULL or chr(173) characters in $string.
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###############################################################################
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$string = preg_replace('/\0+/', '', $string);
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$string = preg_replace('/(\\\\0)+/', '', $string);
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$string = preg_replace('/\xad+/', '', $string); # deals with Opera "feature"
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} # function kses_no_null
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function kses_stripslashes($string)
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###############################################################################
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# This function changes the character sequence \" to just "
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# It leaves all other slashes alone. It's really weird, but the quoting from
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# preg_replace(//e) seems to require this.
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###############################################################################
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return preg_replace('%\\\\"%', '"', $string);
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} # function kses_stripslashes
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function kses_array_lc($inarray)
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###############################################################################
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# This function goes through an array, and changes the keys to all lower case.
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###############################################################################
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foreach ($inarray as $inkey => $inval)
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$outkey = strtolower($inkey);
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$outarray[$outkey] = array();
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foreach ($inval as $inkey2 => $inval2)
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$outkey2 = strtolower($inkey2);
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$outarray[$outkey][$outkey2] = $inval2;
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} # function kses_array_lc
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function kses_js_entities($string)
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###############################################################################
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# This function removes the HTML JavaScript entities found in early versions of
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###############################################################################
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return preg_replace('%&\s*\{[^}]*(\}\s*;?|$)%', '', $string);
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} # function kses_js_entities
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function kses_html_error($string)
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###############################################################################
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# This function deals with parsing errors in kses_hair(). The general plan is
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# to remove everything to and including some whitespace, but it deals with
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# quotes and apostrophes as well.
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###############################################################################
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return preg_replace('/^("[^"]*("|$)|\'[^\']*(\'|$)|\S)*\s*/', '', $string);
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} # function kses_html_error
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function kses_bad_protocol_once($string, $allowed_protocols)
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###############################################################################
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# This function searches for URL protocols at the beginning of $string, while
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# handling whitespace and HTML entities.
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###############################################################################
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return preg_replace('/^((&[^;]*;|[\sA-Za-z0-9])*)'.
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'(:|:|&#[Xx]3[Aa];)\s*/e',
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'kses_bad_protocol_once2("\\1", $allowed_protocols)',
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} # function kses_bad_protocol_once
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function kses_bad_protocol_once2($string, $allowed_protocols)
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###############################################################################
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# This function processes URL protocols, checks to see if they're in the white-
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# list or not, and returns different data depending on the answer.
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###############################################################################
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$string2 = kses_decode_entities($string);
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$string2 = preg_replace('/\s/', '', $string2);
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$string2 = kses_no_null($string2);
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$string2 = strtolower($string2);
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foreach ($allowed_protocols as $one_protocol)
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if (strtolower($one_protocol) == $string2)
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} # function kses_bad_protocol_once2
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function kses_normalize_entities($string)
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###############################################################################
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# This function normalizes HTML entities. It will convert "AT&T" to the correct
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# "AT&T", ":" to ":", "&#XYZZY;" to "&#XYZZY;" and so on.
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###############################################################################
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# Disarm all entities by converting & to &
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$string = str_replace('&', '&', $string);
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# Change back the allowed entities in our entity whitelist
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$string = preg_replace('/&([A-Za-z][A-Za-z0-9]{0,19});/',
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$string = preg_replace('/&#0*([0-9]{1,5});/e',
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'kses_normalize_entities2("\\1")', $string);
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$string = preg_replace('/&#([Xx])0*(([0-9A-Fa-f]{2}){1,2});/',
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'&#\\1\\2;', $string);
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} # function kses_normalize_entities
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function kses_normalize_entities2($i)
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###############################################################################
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# This function helps kses_normalize_entities() to only accept 16 bit values
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# and nothing more for &#number; entities.
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###############################################################################
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return (($i > 65535) ? "&#$i;" : "&#$i;");
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} # function kses_normalize_entities2
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function kses_decode_entities($string)
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###############################################################################
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# This function decodes numeric HTML entities (A and A). It doesn't
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# do anything with other entities like ä, but we don't need them in the
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# URL protocol whitelisting system anyway.
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###############################################################################
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$string = preg_replace('/&#([0-9]+);/e', 'chr("\\1")', $string);
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$string = preg_replace('/&#[Xx]([0-9A-Fa-f]+);/e', 'chr(hexdec("\\1"))',
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} # function kses_decode_entities
added
removed
lib/kses.php
