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Added better cleaning of HTML attributes, using kses library.

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Thanks to Eamon Costello for finding the library and writing the
wrapper functions.
This commit is contained in:
moodler 2004-08-21 04:34:06 +00:00
parent 65fa81403d
commit 3bd7ffec71
2 changed files with 597 additions and 6 deletions

545
lib/kses.php Normal file

@ -0,0 +1,545 @@
<?php
# kses 0.2.1 - HTML/XHTML filter that only allows some elements and attributes
# Copyright (C) 2002, 2003 Ulf Harnhammar
#
# This program is free software and open source software; you can redistribute
# it and/or modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of the License,
# or (at your option) any later version.
#
# This program 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 General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA or visit
# http://www.gnu.org/licenses/gpl.html
#
# *** CONTACT INFORMATION ***
#
# E-mail: metaur at users dot sourceforge dot net
# Web page: http://sourceforge.net/projects/kses
# Paper mail: (not at the moment)
#
# [kses strips evil scripts!]
function kses($string, $allowed_html, $allowed_protocols =
array('http', 'https', 'ftp', 'news', 'nntp', 'telnet',
'gopher', 'mailto'))
###############################################################################
# This function makes sure that only the allowed HTML element names, attribute
# names and attribute values plus only sane HTML entities will occur in
# $string. You have to remove any slashes from PHP's magic quotes before you
# call this function.
###############################################################################
{
$string = kses_no_null($string);
$string = kses_js_entities($string);
$string = kses_normalize_entities($string);
$string = kses_hook($string);
$allowed_html_fixed = kses_array_lc($allowed_html);
return kses_split($string, $allowed_html_fixed, $allowed_protocols);
} # function kses
function kses_hook($string)
###############################################################################
# You add any kses hooks here.
###############################################################################
{
return $string;
} # function kses_hook
function kses_version()
###############################################################################
# This function returns kses' version number.
###############################################################################
{
return '0.2.1';
} # function kses_version
function kses_split($string, $allowed_html, $allowed_protocols)
###############################################################################
# This function searches for HTML tags, no matter how malformed. It also
# matches stray ">" characters.
###############################################################################
{
return preg_replace('%(<'. # EITHER: <
'[^>]*'. # things that aren't >
'(>|$)'. # > or end of string
'|>)%e', # OR: just a >
"kses_split2('\\1', \$allowed_html, ".
'$allowed_protocols)',
$string);
} # function kses_split
function kses_split2($string, $allowed_html, $allowed_protocols)
###############################################################################
# This function does a lot of work. It rejects some very malformed things
# like <:::>. It returns an empty string, if the element isn't allowed (look
# ma, no strip_tags()!). Otherwise it splits the tag into an element and an
# attribute list.
###############################################################################
{
$string = kses_stripslashes($string);
if (substr($string, 0, 1) != '<')
return '&gt;';
# It matched a ">" character
if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $string, $matches))
return '';
# It's seriously malformed
$slash = trim($matches[1]);
$elem = $matches[2];
$attrlist = $matches[3];
if ( !is_array($allowed_html[strtolower($elem)]))
return '';
# They are using a not allowed HTML element
return kses_attr("$slash$elem", $attrlist, $allowed_html,
$allowed_protocols);
} # function kses_split2
function kses_attr($element, $attr, $allowed_html, $allowed_protocols)
###############################################################################
# This function removes all attributes, if none are allowed for this element.
# If some are allowed it calls kses_hair() to split them further, and then it
# builds up new HTML code from the data that kses_hair() returns. It also
# removes "<" and ">" characters, if there are any left. One more thing it
# does is to check if the tag has a closing XHTML slash, and if it does,
# it puts one in the returned code as well.
###############################################################################
{
# Is there a closing XHTML slash at the end of the attributes?
$xhtml_slash = '';
if (preg_match('%\s/\s*$%', $attr))
$xhtml_slash = ' /';
# Are any attributes allowed at all for this element?
if (count($allowed_html[strtolower($element)]) == 0)
return "<$element$xhtml_slash>";
# Split it
$attrarr = kses_hair($attr, $allowed_protocols);
# Go through $attrarr, and save the allowed attributes for this element
# in $attr2
$attr2 = '';
foreach ($attrarr as $arreach)
{
$current = $allowed_html[strtolower($element)]
[strtolower($arreach['name'])];
if ($current == '')
continue; # the attribute is not allowed
if (!is_array($current))
$attr2 .= ' '.$arreach['whole'];
# there are no checks
else
{
# there are some checks
$ok = true;
foreach ($current as $currkey => $currval)
if (!kses_check_attr_val($arreach['value'], $arreach['vless'],
$currkey, $currval))
{ $ok = false; break; }
if ($ok)
$attr2 .= ' '.$arreach['whole']; # it passed them
} # if !is_array($current)
} # foreach
# Remove any "<" or ">" characters
$attr2 = preg_replace('/[<>]/', '', $attr2);
return "<$element$attr2$xhtml_slash>";
} # function kses_attr
function kses_hair($attr, $allowed_protocols)
###############################################################################
# This function does a lot of work. It parses an attribute list into an array
# with attribute data, and tries to do the right thing even if it gets weird
# input. It will add quotes around attribute values that don't have any quotes
# or apostrophes around them, to make it easier to produce HTML code that will
# conform to W3C's HTML specification. It will also remove bad URL protocols
# from attribute values.
###############################################################################
{
$attrarr = array();
$mode = 0;
$attrname = '';
# Loop through the whole attribute list
while (strlen($attr) != 0)
{
$working = 0; # Was the last operation successful?
switch ($mode)
{
case 0: # attribute name, href for instance
if (preg_match('/^([-a-zA-Z]+)/', $attr, $match))
{
$attrname = $match[1];
$working = $mode = 1;
$attr = preg_replace('/^[-a-zA-Z]+/', '', $attr);
}
break;
case 1: # equals sign or valueless ("selected")
if (preg_match('/^\s*=\s*/', $attr)) # equals sign
{
$working = 1; $mode = 2;
$attr = preg_replace('/^\s*=\s*/', '', $attr);
break;
}
if (preg_match('/^\s+/', $attr)) # valueless
{
$working = 1; $mode = 0;
$attrarr[] = array
('name' => $attrname,
'value' => '',
'whole' => $attrname,
'vless' => 'y');
$attr = preg_replace('/^\s+/', '', $attr);
}
break;
case 2: # attribute value, a URL after href= for instance
if (preg_match('/^"([^"]*)"(\s+|$)/', $attr, $match))
# "value"
{
$thisval = kses_bad_protocol($match[1], $allowed_protocols);
$attrarr[] = array
('name' => $attrname,
'value' => $thisval,
'whole' => "$attrname=\"$thisval\"",
'vless' => 'n');
$working = 1; $mode = 0;
$attr = preg_replace('/^"[^"]*"(\s+|$)/', '', $attr);
break;
}
if (preg_match("/^'([^']*)'(\s+|$)/", $attr, $match))
# 'value'
{
$thisval = kses_bad_protocol($match[1], $allowed_protocols);
$attrarr[] = array
('name' => $attrname,
'value' => $thisval,
'whole' => "$attrname='$thisval'",
'vless' => 'n');
$working = 1; $mode = 0;
$attr = preg_replace("/^'[^']*'(\s+|$)/", '', $attr);
break;
}
if (preg_match("%^([^\s\"']+)(\s+|$)%", $attr, $match))
# value
{
$thisval = kses_bad_protocol($match[1], $allowed_protocols);
$attrarr[] = array
('name' => $attrname,
'value' => $thisval,
'whole' => "$attrname=\"$thisval\"",
'vless' => 'n');
# We add quotes to conform to W3C's HTML spec.
$working = 1; $mode = 0;
$attr = preg_replace("%^[^\s\"']+(\s+|$)%", '', $attr);
}
break;
} # switch
if ($working == 0) # not well formed, remove and try again
{
$attr = kses_html_error($attr);
$mode = 0;
}
} # while
if ($mode == 1)
# special case, for when the attribute list ends with a valueless
# attribute like "selected"
$attrarr[] = array
('name' => $attrname,
'value' => '',
'whole' => $attrname,
'vless' => 'y');
return $attrarr;
} # function kses_hair
function kses_check_attr_val($value, $vless, $checkname, $checkvalue)
###############################################################################
# This function performs different checks for attribute values. The currently
# implemented checks are "maxlen", "minlen", "maxval", "minval" and "valueless"
# with even more checks to come soon.
###############################################################################
{
$ok = true;
switch (strtolower($checkname))
{
case 'maxlen':
# The maxlen check makes sure that the attribute value has a length not
# greater than the given value. This can be used to avoid Buffer Overflows
# in WWW clients and various Internet servers.
if (strlen($value) > $checkvalue)
$ok = false;
break;
case 'minlen':
# The minlen check makes sure that the attribute value has a length not
# smaller than the given value.
if (strlen($value) < $checkvalue)
$ok = false;
break;
case 'maxval':
# The maxval check does two things: it checks that the attribute value is
# an integer from 0 and up, without an excessive amount of zeroes or
# whitespace (to avoid Buffer Overflows). It also checks that the attribute
# value is not greater than the given value.
# This check can be used to avoid Denial of Service attacks.
if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
$ok = false;
if ($value > $checkvalue)
$ok = false;
break;
case 'minval':
# The minval check checks that the attribute value is a positive integer,
# and that it is not smaller than the given value.
if (!preg_match('/^\s{0,6}[0-9]{1,6}\s{0,6}$/', $value))
$ok = false;
if ($value < $checkvalue)
$ok = false;
break;
case 'valueless':
# The valueless check checks if the attribute has a value
# (like <a href="blah">) or not (<option selected>). If the given value
# is a "y" or a "Y", the attribute must not have a value.
# If the given value is an "n" or an "N", the attribute must have one.
if (strtolower($checkvalue) != $vless)
$ok = false;
break;
} # switch
return $ok;
} # function kses_check_attr_val
function kses_bad_protocol($string, $allowed_protocols)
###############################################################################
# This function removes all non-allowed protocols from the beginning of
# $string. It ignores whitespace and the case of the letters, and it does
# understand HTML entities. It does its work in a while loop, so it won't be
# fooled by a string like "javascript:javascript:alert(57)".
###############################################################################
{
$string = kses_no_null($string);
$string2 = $string.'a';
while ($string != $string2)
{
$string2 = $string;
$string = kses_bad_protocol_once($string, $allowed_protocols);
} # while
return $string;
} # function kses_bad_protocol
function kses_no_null($string)
###############################################################################
# This function removes any NULL or chr(173) characters in $string.
###############################################################################
{
$string = preg_replace('/\0+/', '', $string);
$string = preg_replace('/(\\\\0)+/', '', $string);
$string = preg_replace('/\xad+/', '', $string); # deals with Opera "feature"
return $string;
} # function kses_no_null
function kses_stripslashes($string)
###############################################################################
# This function changes the character sequence \" to just "
# It leaves all other slashes alone. It's really weird, but the quoting from
# preg_replace(//e) seems to require this.
###############################################################################
{
return preg_replace('%\\\\"%', '"', $string);
} # function kses_stripslashes
function kses_array_lc($inarray)
###############################################################################
# This function goes through an array, and changes the keys to all lower case.
###############################################################################
{
$outarray = array();
foreach ($inarray as $inkey => $inval)
{
$outkey = strtolower($inkey);
$outarray[$outkey] = array();
foreach ($inval as $inkey2 => $inval2)
{
$outkey2 = strtolower($inkey2);
$outarray[$outkey][$outkey2] = $inval2;
} # foreach $inval
} # foreach $inarray
return $outarray;
} # function kses_array_lc
function kses_js_entities($string)
###############################################################################
# This function removes the HTML JavaScript entities found in early versions of
# Netscape 4.
###############################################################################
{
return preg_replace('%&\s*\{[^}]*(\}\s*;?|$)%', '', $string);
} # function kses_js_entities
function kses_html_error($string)
###############################################################################
# This function deals with parsing errors in kses_hair(). The general plan is
# to remove everything to and including some whitespace, but it deals with
# quotes and apostrophes as well.
###############################################################################
{
return preg_replace('/^("[^"]*("|$)|\'[^\']*(\'|$)|\S)*\s*/', '', $string);
} # function kses_html_error
function kses_bad_protocol_once($string, $allowed_protocols)
###############################################################################
# This function searches for URL protocols at the beginning of $string, while
# handling whitespace and HTML entities.
###############################################################################
{
return preg_replace('/^((&[^;]*;|[\sA-Za-z0-9])*)'.
'(:|&#58;|&#[Xx]3[Aa];)\s*/e',
'kses_bad_protocol_once2("\\1", $allowed_protocols)',
$string);
} # function kses_bad_protocol_once
function kses_bad_protocol_once2($string, $allowed_protocols)
###############################################################################
# This function processes URL protocols, checks to see if they're in the white-
# list or not, and returns different data depending on the answer.
###############################################################################
{
$string2 = kses_decode_entities($string);
$string2 = preg_replace('/\s/', '', $string2);
$string2 = kses_no_null($string2);
$string2 = strtolower($string2);
$allowed = false;
foreach ($allowed_protocols as $one_protocol)
if (strtolower($one_protocol) == $string2)
{
$allowed = true;
break;
}
if ($allowed)
return "$string2:";
else
return '';
} # function kses_bad_protocol_once2
function kses_normalize_entities($string)
###############################################################################
# This function normalizes HTML entities. It will convert "AT&T" to the correct
# "AT&amp;T", "&#00058;" to "&#58;", "&#XYZZY;" to "&amp;#XYZZY;" and so on.
###############################################################################
{
# Disarm all entities by converting & to &amp;
$string = str_replace('&', '&amp;', $string);
# Change back the allowed entities in our entity whitelist
$string = preg_replace('/&amp;([A-Za-z][A-Za-z0-9]{0,19});/',
'&\\1;', $string);
$string = preg_replace('/&amp;#0*([0-9]{1,5});/e',
'kses_normalize_entities2("\\1")', $string);
$string = preg_replace('/&amp;#([Xx])0*(([0-9A-Fa-f]{2}){1,2});/',
'&#\\1\\2;', $string);
return $string;
} # function kses_normalize_entities
function kses_normalize_entities2($i)
###############################################################################
# This function helps kses_normalize_entities() to only accept 16 bit values
# and nothing more for &#number; entities.
###############################################################################
{
return (($i > 65535) ? "&amp;#$i;" : "&#$i;");
} # function kses_normalize_entities2
function kses_decode_entities($string)
###############################################################################
# This function decodes numeric HTML entities (&#65; and &#x41;). It doesn't
# do anything with other entities like &auml;, but we don't need them in the
# URL protocol whitelisting system anyway.
###############################################################################
{
$string = preg_replace('/&#([0-9]+);/e', 'chr("\\1")', $string);
$string = preg_replace('/&#[Xx]([0-9A-Fa-f]+);/e', 'chr(hexdec("\\1"))',
$string);
return $string;
} # function kses_decode_entities
?>

58
lib/weblib.php

@ -744,22 +744,68 @@ function clean_text($text, $format=FORMAT_MOODLE) {
/// Remove tags that are not allowed
$text = strip_tags($text, $ALLOWED_TAGS);
/// Munge javascript: label
$text = str_ireplace("javascript:", "Xjavascript:", $text);
$text = str_ireplace("vbscript:", "Xvbscript:", $text);
/// Remove script events
$text = eregi_replace("([^a-z])language([[:space:]]*)=", "\\1Xlanguage=", $text);
$text = eregi_replace("([^a-z])on([a-z]+)([[:space:]]*)=", "\\1Xon\\2=", $text);
/// Remove Javascript entities
$text = eregi_replace('&\{([^};]*)\};', '\1', $text);
/// Clean up embedded scripts and , using kses
$text = cleanAttributes($text);
return $text;
}
}
function cleanAttributes($str){
/// This function takes a string and examines it for html tags.
/// If tags are detected it passes the string to a helper function cleanAttributes2
/// which checks for attributes and filters them for malicious content
/// 17/08/2004 :: Eamon DOT Costello AT dcu DOT ie
$result = preg_replace(
'%(<[^>]*(>|$)|>)%me', #search for html tags
"cleanAttributes2('\\1')",
$str
);
return $result;
}
function cleanAttributes2($htmlTag){
/// This function takes a string with an html tag and strips out any unallowed
/// protocols e.g. javascript:
/// It calls ancillary functions in kses which are prefixed by kses
/// 17/08/2004 :: Eamon DOT Costello AT dcu DOT ie
global $CFG;
require_once("$CFG->libdir/kses.php");
$htmlTag = kses_stripslashes($htmlTag);
if (substr($htmlTag, 0, 1) != '<'){
return '&gt;'; //a single character ">" detected
}
if (!preg_match('%^<\s*(/\s*)?([a-zA-Z0-9]+)([^>]*)>?$%', $htmlTag, $matches)){
return ''; // It's seriously malformed
}
$slash = trim($matches[1]); //trailing xhtml slash
$elem = $matches[2]; //the element name
$attrlist = $matches[3]; // the list of attributes as a string
$allowed_protocols = array('http', 'https', 'ftp', 'news', 'mailto');
$attrArray = kses_hair($attrlist, $allowed_protocols) ;
$attStr = '';
foreach ($attrArray as $arreach)
{
$attStr .= ' '.strtolower($arreach['name']).'="'.strtolower($arreach['value']).'" ';
}
$xhtml_slash = '';
if (preg_match('%/\s*$%', $attrlist)){
$xhtml_slash = ' /';
}
return "<$slash$elem$attStr$xhtml_slash>";
}
function replace_smilies(&$text) {
/// Replaces all known smileys in the text with image equivalents
global $CFG;