genshi.filters.html.HTMLSanitizer

Package genshi :: Package filters :: Module html :: Class HTMLSanitizer |

# Class HTMLSanitizer

    object --+
             |
            HTMLSanitizer

A filter that removes potentially dangerous HTML tags and attributes from the stream.

    >>> from genshi import HTML
    >>> html = HTML('<div><script>alert(document.cookie)</script></div>', encoding='utf-8')
    >>> print(html | HTMLSanitizer())
    <div/>

The default set of safe tags and attributes can be modified when the filter is instantiated. For example, to allow inline `style` attributes, the following instantation would work:

    >>> html = HTML('<div style="background: #000"></div>', encoding='utf-8')
    >>> sanitizer = HTMLSanitizer(safe_attrs=HTMLSanitizer.SAFE_ATTRS | set(['style']))
    >>> print(html | sanitizer)
    <div style="background: #000"/>

Note that even in this case, the filter does attempt to remove dangerous constructs from style attributes:

    >>> html = HTML('<div style="background: url(javascript:void); color: #000"></div>', encoding='utf-8')
    >>> print(html | sanitizer)
    <div style="color: #000"/>

This handles HTML entities, unicode escapes in CSS and Javascript text, as well as a lot of other things. However, the style tag is still excluded by default because it is very hard for such sanitizing to be completely safe, especially considering how much error recovery current web browsers perform.

It also does some basic filtering of CSS properties that may be used for typical phishing attacks. For more sophisticated filtering, this class provides a couple of hooks that can be overridden in sub-classes.

Warning: Note that this special processing of CSS is currently only applied to style attributes, not style elements.

Instance Methods
__init__(self, safe_tags=`frozenset([``'``a``'``,` `'``abbr``'``,` `'``acronym``'``,` `'``address``'``,` `'``area``'``,` `'``b``'``,` `'``bi``...`, safe_attrs=`frozenset([``'``abbr``'``,` `'``accept``'``,` `'``accept-charset``'``,` `'``accesskey``'``,` `'``a``...`, safe_schemes=`frozenset([`None`,` `'``file``'``,` `'``ftp``'``,` `'``http``'``,` `'``https``'``,` `'``mailto``'``])`, uri_attrs=`frozenset([``'``action``'``,` `'``background``'``,` `'``dynsrc``'``,` `'``href``'``,` `'``lowsrc``'``,``...`, safe_css=`frozenset([``'``background``'``,` `'``background-attachment``'``,` `'``background-``...`) Create the sanitizer. |
__call__(self, stream) Apply the filter to the given stream. |
bool |
is_safe_css(self, propname, value) Determine whether the given css property declaration is to be considered safe for inclusion in the output. |
bool |
is_safe_elem(self, tag, attrs) Determine whether the given element should be considered safe for inclusion in the output. |
`bool` |
is_safe_uri(self, uri) Determine whether the given URI is to be considered safe for inclusion in the output. |
`list` |
sanitize_css(self, text) Remove potentially dangerous property declarations from CSS code. |
Inherited from `object`: `__delattr__`, `__format__`, `__getattribute__`, `__hash__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__repr__`, `__setattr__`, `__sizeof__`, `__str__`, `__subclasshook__`

Class Variables
| SAFE_TAGS = ``frozenset([``'``a``'``,` `'``abbr``'``,` `'``acronym``'``,` `'``address``'``,` `'``are``...``
| SAFE_ATTRS = ``frozenset([``'``abbr``'``,` `'``accept``'``,` `'``accept-charset``'``,` `'``a``...``
| SAFE_CSS = ``frozenset([``'``background``'``,` `'``background-attachment``'``,` `'``...``
| SAFE_SCHEMES = ``frozenset([`None`,` `'``file``'``,` `'``ftp``'``,` `'``http``'``,` `'``https``'``...``
| URI_ATTRS = ``frozenset([``'``action``'``,` `'``background``'``,` `'``dynsrc``'``,` `'``href``...``

Properties
Inherited from `object`: `__class__`

Method Details

### __init__(self, safe_tags=`frozenset([``'``a``'``,` `'``abbr``'``,` `'``acronym``'``,` `'``address``'``,` `'``area``'``,` `'``b``'``,` `'``bi``...`, safe_attrs=`frozenset([``'``abbr``'``,` `'``accept``'``,` `'``accept-charset``'``,` `'``accesskey``'``,` `'``a``...`, safe_schemes=`frozenset([`None`,` `'``file``'``,` `'``ftp``'``,` `'``http``'``,` `'``https``'``,` `'``mailto``'``])`, uri_attrs=`frozenset([``'``action``'``,` `'``background``'``,` `'``dynsrc``'``,` `'``href``'``,` `'``lowsrc``'``,``...`, safe_css=`frozenset([``'``background``'``,` `'``background-attachment``'``,` `'``background-``...`) (Constructor) |
Create the sanitizer. The exact set of allowed elements and attributes can be configured. Parameters: `safe_tags` - a set of tag names that are considered safe `safe_attrs` - a set of attribute names that are considered safe `safe_schemes` - a set of URI schemes that are considered safe `uri_attrs` - a set of names of attributes that contain URIs Overrides: object.__init__

### __call__(self, stream) (Call operator) |
Apply the filter to the given stream. Parameters: `stream` - the markup event stream to filter

### is_safe_css(self, propname, value) |
Determine whether the given css property declaration is to be considered safe for inclusion in the output. Parameters: `propname` - the CSS property name `value` - the value of the property Returns: bool whether the property value should be considered safe Since: version 0.6

### is_safe_elem(self, tag, attrs) |
Determine whether the given element should be considered safe for inclusion in the output. Parameters: `tag` (QName) - the tag name of the element `attrs` (Attrs) - the element attributes Returns: bool whether the element should be considered safe Since: version 0.6

### is_safe_uri(self, uri) |
Determine whether the given URI is to be considered safe for inclusion in the output. The default implementation checks whether the scheme of the URI is in the set of allowed URIs (`safe_schemes`).
    >>> sanitizer = HTMLSanitizer()
    >>> sanitizer.is_safe_uri('http://example.org/')
    True
    >>> sanitizer.is_safe_uri('javascript:alert(document.cookie)')
    False
Parameters: `uri` - the URI to check Returns: `bool` `True` if the URI can be considered safe, `False` otherwise Since: version 0.4.3

### sanitize_css(self, text) |
Remove potentially dangerous property declarations from CSS code. In particular, properties using the CSS `url()` function with a scheme that is not considered safe are removed:
    >>> sanitizer = HTMLSanitizer()
    >>> sanitizer.sanitize_css(u'''
    ...   background: url(javascript:alert("foo"));
    ...   color: #000;
    ... ''')
    [u'color: #000']
Also, the proprietary Internet Explorer function `expression()` is always stripped:
    >>> sanitizer.sanitize_css(u'''
    ...   background: #fff;
    ...   color: #000;
    ...   width: e/**/xpression(alert("foo"));
    ... ''')
    [u'background: #fff', u'color: #000']
Parameters: `text` - the CSS text; this is expected to be `unicode` and to not contain any character or numeric references Returns: `list` a list of declarations that are considered safe Since: version 0.4.3

Class Variable Details

  ### SAFE_TAGS Value:
      frozenset(['a',
                 'abbr',
                 'acronym',
                 'address',
                 'area',
                 'b',
                 'big',
                 'blockquote',
      ...

  ### SAFE_ATTRS Value:
      frozenset(['abbr',
                 'accept',
                 'accept-charset',
                 'accesskey',
                 'action',
                 'align',
                 'alt',
                 'axis',
      ...

  ### SAFE_CSS Value:
      frozenset(['background',
                 'background-attachment',
                 'background-color',
                 'background-image',
                 'background-position',
                 'background-repeat',
                 'border',
                 'border-bottom',
      ...

  ### SAFE_SCHEMES Value:
      frozenset([None, 'file', 'ftp', 'http', 'https', 'mailto'])

  ### URI_ATTRS Value:
      frozenset(['action', 'background', 'dynsrc', 'href', 'lowsrc', 'src'])