Source code for bleach.sanitizer

from __future__ import unicode_literals

from itertools import chain
import re

import six
from six.moves.urllib.parse import urlparse
from xml.sax.saxutils import unescape

from bleach import html5lib_shim
from bleach.utils import alphabetize_attributes, force_unicode


#: List of allowed tags
ALLOWED_TAGS = [
    'a',
    'abbr',
    'acronym',
    'b',
    'blockquote',
    'code',
    'em',
    'i',
    'li',
    'ol',
    'strong',
    'ul',
]


#: Map of allowed attributes by tag
ALLOWED_ATTRIBUTES = {
    'a': ['href', 'title'],
    'abbr': ['title'],
    'acronym': ['title'],
}

#: List of allowed styles
ALLOWED_STYLES = []

#: List of allowed protocols
ALLOWED_PROTOCOLS = ['http', 'https', 'mailto']

#: Invisible characters--0 to and including 31 except 9 (tab), 10 (lf), and 13 (cr)
INVISIBLE_CHARACTERS = ''.join([chr(c) for c in chain(range(0, 9), range(11, 13), range(14, 32))])

#: Regexp for characters that are invisible
INVISIBLE_CHARACTERS_RE = re.compile(
    '[' + INVISIBLE_CHARACTERS + ']',
    re.UNICODE
)

#: String to replace invisible characters with. This can be a character, a
#: string, or even a function that takes a Python re matchobj
INVISIBLE_REPLACEMENT_CHAR = '?'


[docs]class Cleaner(object): """Cleaner for cleaning HTML fragments of malicious content This cleaner is a security-focused function whose sole purpose is to remove malicious content from a string such that it can be displayed as content in a web page. To use:: from bleach.sanitizer import Cleaner cleaner = Cleaner() for text in all_the_yucky_things: sanitized = cleaner.clean(text) .. Note:: This cleaner is not designed to use to transform content to be used in non-web-page contexts. .. Warning:: This cleaner is not thread-safe--the html parser has internal state. Create a separate cleaner per thread! """ def __init__(self, tags=ALLOWED_TAGS, attributes=ALLOWED_ATTRIBUTES, styles=ALLOWED_STYLES, protocols=ALLOWED_PROTOCOLS, strip=False, strip_comments=True, filters=None): """Initializes a Cleaner :arg list tags: allowed list of tags; defaults to ``bleach.sanitizer.ALLOWED_TAGS`` :arg dict attributes: allowed attributes; can be a callable, list or dict; defaults to ``bleach.sanitizer.ALLOWED_ATTRIBUTES`` :arg list styles: allowed list of css styles; defaults to ``bleach.sanitizer.ALLOWED_STYLES`` :arg list protocols: allowed list of protocols for links; defaults to ``bleach.sanitizer.ALLOWED_PROTOCOLS`` :arg bool strip: whether or not to strip disallowed elements :arg bool strip_comments: whether or not to strip HTML comments :arg list filters: list of html5lib Filter classes to pass streamed content through .. seealso:: http://html5lib.readthedocs.io/en/latest/movingparts.html#filters .. Warning:: Using filters changes the output of ``bleach.Cleaner.clean``. Make sure the way the filters change the output are secure. """ self.tags = tags self.attributes = attributes self.styles = styles self.protocols = protocols self.strip = strip self.strip_comments = strip_comments self.filters = filters or [] self.parser = html5lib_shim.BleachHTMLParser( tags=self.tags, strip=self.strip, consume_entities=False, namespaceHTMLElements=False ) self.walker = html5lib_shim.getTreeWalker('etree') self.serializer = html5lib_shim.BleachHTMLSerializer( quote_attr_values='always', omit_optional_tags=False, escape_lt_in_attrs=True, # We want to leave entities as they are without escaping or # resolving or expanding resolve_entities=False, # Bleach has its own sanitizer, so don't use the html5lib one sanitize=False, # Bleach sanitizer alphabetizes already, so don't use the html5lib one alphabetical_attributes=False, )
[docs] def clean(self, text): """Cleans text and returns sanitized result as unicode :arg str text: text to be cleaned :returns: sanitized text as unicode :raises TypeError: if ``text`` is not a text type """ if not isinstance(text, six.string_types): message = "argument cannot be of '{name}' type, must be of text type".format( name=text.__class__.__name__) raise TypeError(message) if not text: return u'' text = force_unicode(text) dom = self.parser.parseFragment(text) filtered = BleachSanitizerFilter( source=self.walker(dom), # Bleach-sanitizer-specific things attributes=self.attributes, strip_disallowed_elements=self.strip, strip_html_comments=self.strip_comments, # html5lib-sanitizer things allowed_elements=self.tags, allowed_css_properties=self.styles, allowed_protocols=self.protocols, allowed_svg_properties=[], ) # Apply any filters after the BleachSanitizerFilter for filter_class in self.filters: filtered = filter_class(source=filtered) return self.serializer.render(filtered)
def attribute_filter_factory(attributes): """Generates attribute filter function for the given attributes value The attributes value can take one of several shapes. This returns a filter function appropriate to the attributes value. One nice thing about this is that there's less if/then shenanigans in the ``allow_token`` method. """ if callable(attributes): return attributes if isinstance(attributes, dict): def _attr_filter(tag, attr, value): if tag in attributes: attr_val = attributes[tag] if callable(attr_val): return attr_val(tag, attr, value) if attr in attr_val: return True if '*' in attributes: attr_val = attributes['*'] if callable(attr_val): return attr_val(tag, attr, value) return attr in attr_val return False return _attr_filter if isinstance(attributes, list): def _attr_filter(tag, attr, value): return attr in attributes return _attr_filter raise ValueError('attributes needs to be a callable, a list or a dict')
[docs]class BleachSanitizerFilter(html5lib_shim.SanitizerFilter): """html5lib Filter that sanitizes text This filter can be used anywhere html5lib filters can be used. """ def __init__(self, source, attributes=ALLOWED_ATTRIBUTES, strip_disallowed_elements=False, strip_html_comments=True, **kwargs): """Creates a BleachSanitizerFilter instance :arg Treewalker source: stream :arg list tags: allowed list of tags; defaults to ``bleach.sanitizer.ALLOWED_TAGS`` :arg dict attributes: allowed attributes; can be a callable, list or dict; defaults to ``bleach.sanitizer.ALLOWED_ATTRIBUTES`` :arg list styles: allowed list of css styles; defaults to ``bleach.sanitizer.ALLOWED_STYLES`` :arg list protocols: allowed list of protocols for links; defaults to ``bleach.sanitizer.ALLOWED_PROTOCOLS`` :arg bool strip_disallowed_elements: whether or not to strip disallowed elements :arg bool strip_html_comments: whether or not to strip HTML comments """ self.attr_filter = attribute_filter_factory(attributes) self.strip_disallowed_elements = strip_disallowed_elements self.strip_html_comments = strip_html_comments return super(BleachSanitizerFilter, self).__init__(source, **kwargs) def sanitize_stream(self, token_iterator): for token in token_iterator: ret = self.sanitize_token(token) if not ret: continue if isinstance(ret, list): for subtoken in ret: yield subtoken else: yield ret def merge_characters(self, token_iterator): """Merge consecutive Characters tokens in a stream""" characters_buffer = [] for token in token_iterator: if characters_buffer: if token['type'] == 'Characters': characters_buffer.append(token) continue else: # Merge all the characters tokens together into one and then # operate on it. new_token = { 'data': ''.join([char_token['data'] for char_token in characters_buffer]), 'type': 'Characters' } characters_buffer = [] yield new_token elif token['type'] == 'Characters': characters_buffer.append(token) continue yield token new_token = { 'data': ''.join([char_token['data'] for char_token in characters_buffer]), 'type': 'Characters' } yield new_token def __iter__(self): return self.merge_characters(self.sanitize_stream(html5lib_shim.Filter.__iter__(self))) def sanitize_token(self, token): """Sanitize a token either by HTML-encoding or dropping. Unlike sanitizer.Filter, allowed_attributes can be a dict of {'tag': ['attribute', 'pairs'], 'tag': callable}. Here callable is a function with two arguments of attribute name and value. It should return true of false. Also gives the option to strip tags instead of encoding. :arg dict token: token to sanitize :returns: token or list of tokens """ token_type = token['type'] if token_type in ['StartTag', 'EndTag', 'EmptyTag']: if token['name'] in self.allowed_elements: return self.allow_token(token) elif self.strip_disallowed_elements: return None else: if 'data' in token: # Alphabetize the attributes before calling .disallowed_token() # so that the resulting string is stable token['data'] = alphabetize_attributes(token['data']) return self.disallowed_token(token) elif token_type == 'Comment': if not self.strip_html_comments: return token else: return None elif token_type == 'Characters': return self.sanitize_characters(token) else: return token def sanitize_characters(self, token): """Handles Characters tokens Our overridden tokenizer doesn't do anything with entities. However, that means that the serializer will convert all ``&`` in Characters tokens to ``&amp;``. Since we don't want that, we extract entities here and convert them to Entity tokens so the serializer will let them be. :arg token: the Characters token to work on :returns: a list of tokens """ data = token.get('data', '') if not data: return token data = INVISIBLE_CHARACTERS_RE.sub(INVISIBLE_REPLACEMENT_CHAR, data) token['data'] = data # If there isn't a & in the data, we can return now if '&' not in data: return token new_tokens = [] # For each possible entity that starts with a "&", we try to extract an # actual entity and re-tokenize accordingly for part in html5lib_shim.next_possible_entity(data): if not part: continue if part.startswith('&'): entity = html5lib_shim.match_entity(part) if entity is not None: new_tokens.append({'type': 'Entity', 'name': entity}) # Length of the entity plus 2--one for & at the beginning # and and one for ; at the end remainder = part[len(entity) + 2:] if remainder: new_tokens.append({'type': 'Characters', 'data': remainder}) continue new_tokens.append({'type': 'Characters', 'data': part}) return new_tokens def sanitize_uri_value(self, value, allowed_protocols): """Checks a uri value to see if it's allowed :arg value: the uri value to sanitize :arg allowed_protocols: list of allowed protocols :returns: allowed value or None """ # NOTE(willkg): This transforms the value into one that's easier to # match and verify, but shouldn't get returned since it's vastly # different than the original value. # Convert all character entities in the value new_value = html5lib_shim.convert_entities(value) # Nix backtick, space characters, and control characters new_value = re.sub( r"[`\000-\040\177-\240\s]+", '', new_value ) # Remove REPLACEMENT characters new_value = new_value.replace('\ufffd', '') # Lowercase it--this breaks the value, but makes it easier to match # against new_value = new_value.lower() try: # Drop attributes with uri values that have protocols that aren't # allowed parsed = urlparse(new_value) except ValueError: # URI is impossible to parse, therefore it's not allowed return None if parsed.scheme: # If urlparse found a scheme, check that if parsed.scheme in allowed_protocols: return value else: # Allow uris that are just an anchor if new_value.startswith('#'): return value # Handle protocols that urlparse doesn't recognize like "myprotocol" if ':' in new_value and new_value.split(':')[0] in allowed_protocols: return value # If there's no protocol/scheme specified, then assume it's "http" # and see if that's allowed if 'http' in allowed_protocols: return value return None def allow_token(self, token): """Handles the case where we're allowing the tag""" if 'data' in token: # Loop through all the attributes and drop the ones that are not # allowed, are unsafe or break other rules. Additionally, fix # attribute values that need fixing. # # At the end of this loop, we have the final set of attributes # we're keeping. attrs = {} for namespaced_name, val in token['data'].items(): namespace, name = namespaced_name # Drop attributes that are not explicitly allowed # # NOTE(willkg): We pass in the attribute name--not a namespaced # name. if not self.attr_filter(token['name'], name, val): continue # Drop attributes with uri values that use a disallowed protocol # Sanitize attributes with uri values if namespaced_name in self.attr_val_is_uri: new_value = self.sanitize_uri_value(val, self.allowed_protocols) if new_value is None: continue val = new_value # Drop values in svg attrs with non-local IRIs if namespaced_name in self.svg_attr_val_allows_ref: new_val = re.sub(r'url\s*\(\s*[^#\s][^)]+?\)', ' ', unescape(val)) new_val = new_val.strip() if not new_val: continue else: # Replace the val with the unescaped version because # it's a iri val = new_val # Drop href and xlink:href attr for svg elements with non-local IRIs if (None, token['name']) in self.svg_allow_local_href: if namespaced_name in [ (None, 'href'), (html5lib_shim.namespaces['xlink'], 'href') ]: if re.search(r'^\s*[^#\s]', val): continue # If it's a style attribute, sanitize it if namespaced_name == (None, u'style'): val = self.sanitize_css(val) # At this point, we want to keep the attribute, so add it in attrs[namespaced_name] = val token['data'] = alphabetize_attributes(attrs) return token def disallowed_token(self, token): token_type = token["type"] if token_type == "EndTag": token["data"] = "</%s>" % token["name"] elif token["data"]: assert token_type in ("StartTag", "EmptyTag") attrs = [] for (ns, name), v in token["data"].items(): # If we end up with a namespace, but no name, switch them so we # have a valid name to use. if ns and not name: ns, name = name, ns # Figure out namespaced name if the namespace is appropriate # and exists; if the ns isn't in prefixes, then drop it. if ns is None or ns not in html5lib_shim.prefixes: namespaced_name = name else: namespaced_name = '%s:%s' % (html5lib_shim.prefixes[ns], name) attrs.append(' %s="%s"' % ( namespaced_name, # NOTE(willkg): HTMLSerializer escapes attribute values # already, so if we do it here (like HTMLSerializer does), # then we end up double-escaping. v) ) token["data"] = "<%s%s>" % (token["name"], ''.join(attrs)) else: token["data"] = "<%s>" % token["name"] if token.get("selfClosing"): token["data"] = token["data"][:-1] + "/>" token["type"] = "Characters" del token["name"] return token def sanitize_css(self, style): """Sanitizes css in style tags""" # Convert entities in the style so that it can be parsed as CSS style = html5lib_shim.convert_entities(style) # Drop any url values before we do anything else style = re.compile(r'url\s*\(\s*[^\s)]+?\s*\)\s*').sub(' ', style) # The gauntlet of sanitization # Validate the css in the style tag and if it's not valid, then drop # the whole thing. parts = style.split(';') gauntlet = re.compile( r"""^([-/:,#%.'"\sa-zA-Z0-9!]|\w-\w|'[\s\w]+'\s*|"[\s\w]+"|\([\d,%\.\s]+\))*$""" ) for part in parts: if not gauntlet.match(part): return '' if not re.match(r"^\s*([-\w]+\s*:[^:;]*(;\s*|$))*$", style): return '' clean = [] for prop, value in re.findall(r'([-\w]+)\s*:\s*([^:;]*)', style): if not value: continue if prop.lower() in self.allowed_css_properties: clean.append(prop + ': ' + value + ';') elif prop.lower() in self.allowed_svg_properties: clean.append(prop + ': ' + value + ';') return ' '.join(clean)