Provided by: libmojomojo-perl_1.10+dfsg-1_all bug

NAME

       MojoMojo::Declaw - Cleans HTML as well as CSS of scripting and other executable contents, and neutralises
       XSS attacks.  Derived from HTML::Defang version 1.01.

SYNOPSIS

         my $InputHtml = "<html><body></body></html>";

         my $Defang = MojoMojo::Declaw->new(
           context => $Self,
           fix_mismatched_tags => 1,
           tags_to_callback => [ br embed img ],
           tags_callback => \&DefangTagsCallback,
           url_callback => \&DefangUrlCallback,
           css_callback => \&DefangCssCallback,
           attribs_to_callback => [ qw(border src) ],
           attribs_callback => \&DefangAttribsCallback
         );

         my $SanitizedHtml = $Defang->defang($InputHtml);

         # Callback for custom handling specific HTML tags
         sub DefangTagsCallback {
           my ($Self, $Defang, $OpenAngle, $lcTag, $IsEndTag, $AttributeHash, $CloseAngle, $HtmlR, $OutR) = @_;
           return 1 if $lcTag eq 'br';    # Explicitly defang this tag, eventhough safe
           return 0 if $lcTag eq 'embed'; # Explicitly whitelist this tag, eventhough unsafe
           return 2 if $lcTag eq 'img';   # I am not sure what to do with this tag, so process as HTML::Defang normally would
         }

         # Callback for custom handling URLs in HTML attributes as well as style tag/attribute declarations
         sub DefangUrlCallback {
           my ($Self, $Defang, $lcTag, $lcAttrKey, $AttrValR, $AttributeHash, $HtmlR) = @_;
           return 0 if $$AttrValR =~ /safesite.com/i; # Explicitly allow this URL in tag attributes or stylesheets
           return 1 if $$AttrValR =~ /evilsite.com/i; # Explicitly defang this URL in tag attributes or stylesheets
         }

         # Callback for custom handling style tags/attributes
         sub DefangCssCallback {
           my ($Self, $Defang, $Selectors, $SelectorRules, $Tag, $IsAttr) = @_;
           my $i = 0;
           foreach (@$Selectors) {
             my $SelectorRule = $$SelectorRules[$i];
             foreach my $KeyValueRules (@$SelectorRule) {
               foreach my $KeyValueRule (@$KeyValueRules) {
                 my ($Key, $Value) = @$KeyValueRule;
                 $$KeyValueRule[2] = 1 if $Value =~ '!important';                  # Comment out any '!important' directive
                 $$KeyValueRule[2] = 1 if $Key =~ 'position' && $Value =~ 'fixed'; # Comment out any 'position=fixed;' declaration
               }
             }
             $i++;
           }
         }

         # Callback for custom handling HTML tag attributes
         sub DefangAttribsCallback {
           my ($Self, $Defang, $lcTag, $lcAttrKey, $AttrValR, $HtmlR) = @_;
           $$AttrValR = '0' if $lcAttrKey eq 'border';  # Change all 'border' attribute values to zero.
           return 1 if $lcAttrKey eq 'src';             # Defang all 'src' attributes
           return 0;
         }

DESCRIPTION

       This module accepts an input HTML and/or CSS string and removes any executable code including scripting,
       embedded objects, applets, etc., and neutralises any XSS attacks. A whitelist based approach is used
       which means only HTML known to be safe is allowed through.

       HTML::Defang uses a custom html tag parser. The parser has been designed and tested to work with nasty
       real world html and to try and emulate as close as possible what browsers actually do with strange
       looking constructs. The test suite has been built based on examples from a range of sources such as
       http://ha.ckers.org/xss.html and http://imfo.ru/csstest/css_hacks/import.php to ensure that as many as
       possible XSS attack scenarios have been dealt with.

       HTML::Defang can make callbacks to client code when it encounters the following:

       •   When a specified tag is parsed

       •   When a specified attribute is parsed

       •   When a URL is parsed as part of an HTML attribute, or CSS property value.

       •   When style data is parsed, as part of an HTML style attribute, or as part of an HTML <style> tag.

       The callbacks include details about the current tag/attribute that is being parsed, and also gives a
       scalar reference to the input HTML. Querying pos() on the input HTML should indicate where the module is
       with parsing. This gives the client code flexibility in working with HTML::Declaw.

       HTML::Declaw can defang whole tags, any attribute in a tag, any URL that appear as an attribute or style
       property, or any CSS declaration in a declaration block in a style rule. This helps one to precisely
       block the most specific unwanted elements in the contents(for example, block just an offending attribute
       instead of the whole tag), while retaining any safe HTML/CSS.

CONSTRUCTOR

       MojoMojo::Declaw->new(%Options)
           Constructs a new HTML::Declaw object. The following options are supported:

           Options
               tags_to_callback
                   Array reference of tags for which a call back should be made. If a tag in this array is
                   parsed, the subroutine tags_callback() is invoked.

               attribs_to_callback
                   Array reference of tag attributes for which a call back should be made. If an attribute in
                   this array is parsed, the subroutine attribs_callback() is invoked.

               tags_callback
                   Subroutine reference to be invoked when a tag listed in @$tags_to_callback is parsed.

               attribs_callback
                   Subroutine reference to be invoked when an attribute listed in @$attribs_to_callback is
                   parsed.

               url_callback
                   Subroutine reference to be invoked when a URL is detected in an HTML tag attribute or a CSS
                   property.

               css_callback
                   Subroutine reference to be invoked when CSS data is found either as the contents of a 'style'
                   attribute in an HTML tag, or as the contents of a <style> HTML tag.

               fix_mismatched_tags
                   This property, if set, fixes mismatched tags in the HTML input. By default, tags present in
                   the default %mismatched_tags_to_fix hash are fixed. This set of tags can be overridden by
                   passing in an array reference $mismatched_tags_to_fix to the constructor. Any opened tags in
                   the set are automatically closed if no corresponding closing tag is found. If an unbalanced
                   closing tag is found, that is commented out.

               mismatched_tags_to_fix
                   Array reference of tags for which the code would check for matching opening and closing tags.
                   See the property $fix_mismatched_tags.

               context
                   You can pass an arbitrary scalar as a 'context' value that's then passed as the first
                   parameter to all callback functions. Most commonly this is something like '$Self'

               Debug
                   If set, prints debugging output.

CALLBACK METHODS

       COMMON PARAMETERS
           A number of the callbacks share the same parameters. These common parameters are documented here.
           Certain variables may have specific meanings in certain callbacks, so be sure to check the
           documentation for that method first before referring this section.

           $context
               You can pass an arbitrary scalar as a 'context' value that's then passed as the first parameter
               to all callback functions. Most commonly this is something like '$Self'

           $Defang
               Current HTML::Declaw instance

           $OpenAngle
               Opening angle(<) sign of the current tag.

           $lcTag
               Lower case version of the HTML tag that is currently being parsed.

           $IsEndTag
               Has the value '/' if the current tag is a closing tag.

           $AttributeHash
               A reference to a hash containing the attributes of the current tag and their values. Each value
               is a scalar reference to the value, rather than just a scalar value. You can add attributes
               (remember to make it a scalar ref, eg $AttributeHash{"newattr"} = \"newval"), delete attributes,
               or modify attribute values in this hash, and any changes you make will be incorporated into the
               output HTML stream.

               The attribute values will have any entity references decoded before being passed to you, and any
               unsafe values we be re-encoded back into the HTML stream.

               So for instance, the tag:

                 <div title="&lt;&quot;Hi there &#x003C;">

               Will have the attribute hash:

                 { title => \q[<"Hi there <] }

               And will be turned back into the HTML on output:

                 <div title="&lt;&quot;Hi there &lt;">

           $CloseAngle
               Anything after the end of last attribute including the closing HTML angle(>)

           $HtmlR
               A scalar reference to the input HTML. The input HTML is parsed using m/\G$SomeRegex/c constructs,
               so to continue from where HTML:Defang left, clients can use m/\G$SomeRegex/c for further
               processing on the input. This will resume parsing from where HTML::Declaw left. One can also use
               the pos() function to determine where HTML::Declaw left off. This combined with the
               add_to_output() method should give reasonable flexibility for the client to process the input.

           $OutR
               A scalar reference to the processed output HTML so far.

       tags_callback($context, $Defang, $OpenAngle, $lcTag, $IsEndTag, $AttributeHash, $CloseAngle, $HtmlR,
       $OutR)
           If $Defang->{tags_callback} exists, and HTML::Declaw has parsed a tag preset in
           $Defang->{tags_to_callback}, the above callback is made to the client code. The return value of this
           method determines whether the tag is defanged or not. More details below.

           Return values
               0   The current tag will not be defanged.

               1   The current tag will be defanged.

               2   The current tag will be processed normally by HTML:Defang as if there was no callback method
                   specified.

       attribs_callback($context, $Defang, $lcTag, $lcAttrKey, $AttrVal, $HtmlR, $OutR)
           If $Defang->{attribs_callback} exists, and HTML::Declaw has parsed an attribute present in
           $Defang->{attribs_to_callback}, the above callback is made to the client code. The return value of
           this method determines whether the attribute is defanged or not. More details below.

           Method parameters
               $lcAttrKey
                   Lower case version of the HTML attribute that is currently being parsed.

               $AttrVal
                   Reference to the HTML attribute value that is currently being parsed.

                   See $AttributeHash for details of decoding.

           Return values
               0   The current attribute will not be defanged.

               1   The current attribute will be defanged.

               2   The current attribute will be processed normally by HTML:Defang as if there was no callback
                   method specified.

       url_callback($context, $Defang, $lcTag, $lcAttrKey, $AttrVal, $AttributeHash, $HtmlR, $OutR)
           If $Defang->{url_callback} exists, and HTML::Declaw has parsed a URL, the above callback is made to
           the client code. The return value of this method determines whether the attribute containing the URL
           is defanged or not. URL callbacks can be made from <style> tags as well style attributes, in which
           case the particular style declaration will be commented out. More details below.

           Method parameters
               $lcAttrKey
                   Lower case version of the HTML attribute that is currently being parsed. However if this
                   callback is made as a result of parsing a URL in a style attribute, $lcAttrKey will be set to
                   the string style, or will be set to undef if this callback is made as a result of parsing a
                   URL inside a style tag.

               $AttrVal
                   Reference to the URL value that is currently being parsed.

               $AttributeHash
                   A reference to a hash containing the attributes of the current tag and their values. Each
                   value is a scalar reference to the value, rather than just a scalar value. You can add
                   attributes (remember to make it a scalar ref, eg $AttributeHash{"newattr"} = \"newval"),
                   delete attributes, or modify attribute values in this hash, and any changes you make will be
                   incorporated into the output HTML stream. Will be set to undef if the callback is made due to
                   URL in a <style> tag or attribute.

           Return values
               0   The current URL will not be defanged.

               1   The current URL will be defanged.

               2   The current URL will be processed normally by HTML:Defang as if there was no callback method
                   specified.

       css_callback($context, $Defang, $Selectors, $SelectorRules, $lcTag, $IsAttr, $OutR)
           If $Defang->{css_callback} exists, and HTML::Declaw has parsed a <style> tag or style attribtue, the
           above callback is made to the client code. The return value of this method determines whether a
           particular declaration in the style rules is defanged or not. More details below.

           Method parameters
               $Selectors
                   Reference to an array containing the selectors in a style tag or attribute.

               $SelectorRules
                   Reference to an array containing the style declaration blocks of all selectors in a style tag
                   or attribute. Consider the below CSS:

                     a { b:c; d:e}
                     j { k:l; m:n}

                   The declaration blocks will get parsed into the following data structure:

                     [
                       [
                         [ "b", "c", 2],
                         [ "d", "e", 2]
                       ],
                       [
                         [ "k", "l", 2],
                         [ "m", "n", 2]
                       ]
                     ]

                   So, generally each property:value pair in a declaration is parsed into an array of the form

                     ["property", "value", X]

                   where X can be 0, 1 or 2, and 2 the default value. A client can manipulate this value to
                   instruct HTML::Declaw to defang this property:value pair.

                   0 - Do not defang

                   1 - Defang the style:property value

                   2 - Process this as if there is no callback specified

               $IsAttr
                   True if the currently processed item is a style attribute. False if the currently processed
                   item is a style tag.

METHODS

       PUBLIC METHODS
           defang($InputHtml)
               Cleans up $InputHtml of any executable code including scripting, embedded objects, applets, etc.,
               and defang any XSS attacks.

               Method parameters
                   $InputHtml
                       The input HTML string that needs to be sanitized.

               Returns the cleaned HTML. If fix_mismatched_tags is set, any tags that appear in
               @$mismatched_tags_to_fix that are unbalanced are automatically commented or closed.

           add_to_output($String)
               Appends $String to the output after the current parsed tag ends. Can be used by client code in
               callback methods to add HTML text to the processed output. If the HTML text needs to be defanged,
               client code can safely call HTML::Declaw->defang() recursively from within the callback.

               Method parameters
                   $String
                       The string that is added after the current parsed tag ends.

       defang_and_add_to_output
           defang and add result to output

       INTERNAL METHODS
           Generally these methods never need to be called by users of the class, because they'll be called
           internally as the appropriate tags are encountered, but they may be useful for some users in some
           cases.

           defang_script($OutR, $HtmlR, $TagOps, $OpenAngle, $IsEndTag, $Tag, $TagTrail, $Attributes,
           $CloseAngle)
               This method is invoked when a <script> tag is parsed. Defangs the <script> opening tag, and any
               closing tag. Any scripting content is also commented out, so browsers don't display them.

               Returns 1 to indicate that the <script> tag must be defanged.

               Method parameters
                   $OutR
                       A reference to the processed output HTML before the tag that is currently being parsed.

                   $HtmlR
                       A scalar reference to the input HTML.

                   $TagOps
                       Indicates what operation should be done on a tag. Can be undefined, integer or code
                       reference. Undefined indicates an unknown tag to HTML::Declaw, 1 indicates a known safe
                       tag, 0 indicates a known unsafe tag, and a code reference indicates a subroutine that
                       should be called to parse the current tag. For example, <style> and <script> tags are
                       parsed by dedicated subroutines.

                   $OpenAngle
                       Opening angle(<) sign of the current tag.

                   $IsEndTag
                       Has the value '/' if the current tag is a closing tag.

                   $Tag
                       The HTML tag that is currently being parsed.

                   $TagTrail
                       Any space after the tag, but before attributes.

                   $Attributes
                       A reference to an array of the attributes and their values, including any surrouding
                       spaces. Each element of the array is added by 'push' calls like below.

                         push @$Attributes, [ $AttributeName, $SpaceBeforeEquals, $EqualsAndSubsequentSpace, $QuoteChar, $AttributeValue, $QuoteChar, $SpaceAfterAtributeValue ];

                   $CloseAngle
                       Anything after the end of last attribute including the closing HTML angle(>)

           defang_style($OutR, $HtmlR, $TagOps, $OpenAngle, $IsEndTag, $Tag, $TagTrail, $Attributes,
           $CloseAngle, $IsAttr)
               Builds a list of selectors and declarations from HTML style tags as well as style attributes in
               HTML tags and calls defang_stylerule() to do the actual defanging.

               Returns 0 to indicate that style tags must not be defanged.

               Method parameters
                   $IsAttr
                       Whether we are currently parsing a style attribute or style tag. $IsAttr will be true if
                       we are currently parsing a style attribute.

                   For a description of other parameters, see documentation of defang_script() method

           cleanup_style($StyleString)
               Helper function to clean up CSS data. This function directly operates on the input string without
               taking a copy.

               Method parameters
                   $StyleString
                       The input style string that is cleaned.

           defang_stylerule($SelectorsIn, $StyleRules, $lcTag, $IsAttr, $HtmlR, $OutR)
               Defangs style data.

               Method parameters
                   $SelectorsIn
                       An array reference to the selectors in the style tag/attribute contents.

                   $StyleRules
                       An array reference to the declaration blocks in the style tag/attribute contents.

                   $lcTag
                       Lower case version of the HTML tag that is currently being parsed.

                   $IsAttr
                       Whether we are currently parsing a style attribute or style tag. $IsAttr will be true if
                       we are currently parsing a style attribute.

                   $HtmlR
                       A scalar reference to the input HTML.

                   $OutR
                       A scalar reference to the processed output so far.

           defang_attributes($OutR, $HtmlR, $TagOps, $OpenAngle, $IsEndTag, $Tag, $TagTrail, $Attributes,
           $CloseAngle)
               Defangs attributes, defangs tags, does tag, attrib, css and url callbacks.

               Method parameters
                   For a description of the method parameters, see documentation of defang_script() method

           cleanup_attribute($AttributeString)
               Helper function to cleanup attributes

               Method parameters
                   $AttributeString
                       The value of the attribute.

   get_applicable_charset
       Get the charset from the content meta attribute?

SEE ALSO

       HTML::Defang, <http://mailtools.anomy.net/>, <http://htmlcleaner.sourceforge.net/>, HTML::StripScripts,
       HTML::Detoxifier, HTML::Sanitizer, HTML::Scrubber

AUTHOR

       Kurian Jose Aerthail <cpan@kurianja.fastmail.fm>. Thanks to Rob Mueller <cpan@robm.fastmail.fm> for
       initial code, guidance and support and bug fixes.

COPYRIGHT AND LICENSE

       HTML::Declaw is a modifed version of HTML::Defang which has the following license:

       Copyright (C) 2003-2009 by The FastMail Partnership

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself.