Source code for bleach.sanitizer

from itertools import chain
import re
import warnings

from xml.sax.saxutils import unescape

from bleach import html5lib_shim
from bleach import parse_shim


#: 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 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: """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, protocols=ALLOWED_PROTOCOLS, strip=False, strip_comments=True, filters=None, css_sanitizer=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 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. :arg CSSSanitizer css_sanitizer: instance with a "sanitize_css" method for sanitizing style attribute values and style text; defaults to None """ self.tags = tags self.attributes = attributes self.protocols = protocols self.strip = strip self.strip_comments = strip_comments self.filters = filters or [] self.css_sanitizer = css_sanitizer 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, # clean preserves attr order 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, str): message = ( "argument cannot be of '{name}' type, must be of text type".format( name=text.__class__.__name__ ) ) raise TypeError(message) if not text: return "" 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, css_sanitizer=self.css_sanitizer, # html5lib-sanitizer things allowed_elements=self.tags, allowed_protocols=self.protocols, ) # 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, allowed_elements=ALLOWED_TAGS, attributes=ALLOWED_ATTRIBUTES, allowed_protocols=ALLOWED_PROTOCOLS, strip_disallowed_elements=False, strip_html_comments=True, css_sanitizer=None, **kwargs, ): """Creates a BleachSanitizerFilter instance :arg source: html5lib TreeWalker stream as an html5lib TreeWalker :arg list allowed_elements: 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 allowed_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 :arg CSSSanitizer css_sanitizer: instance with a "sanitize_css" method for sanitizing style attribute values and style text; defaults to None """ self.attr_filter = attribute_filter_factory(attributes) self.strip_disallowed_elements = strip_disallowed_elements self.strip_html_comments = strip_html_comments self.css_sanitizer = css_sanitizer # filter out html5lib deprecation warnings to use bleach from BleachSanitizerFilter init warnings.filterwarnings( "ignore", message="html5lib's sanitizer is deprecated", category=DeprecationWarning, module="bleach._vendor.html5lib", ) return super().__init__( source, allowed_elements=allowed_elements, allowed_protocols=allowed_protocols, **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): yield from ret 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: return self.disallowed_token(token) elif token_type == "Comment": if not self.strip_html_comments: # call lxml.sax.saxutils to escape &, <, and > in addition to " and ' token["data"] = html5lib_shim.escape( token["data"], entities={'"': "&quot;", "'": "&#x27;"} ) 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: if entity == "amp": # LinkifyFilter can't match urls across token boundaries # which is problematic with &amp; since that shows up in # querystrings all the time. This special-cases &amp; # and converts it to a & and sticks it in as a # Characters token. It'll get merged with surrounding # tokens in the BleachSanitizerfilter.__iter__ and # escaped in the serializer. new_tokens.append({"type": "Characters", "data": "&"}) else: new_tokens.append({"type": "Entity", "name": entity}) # Length of the entity plus 2--one for & at the beginning # 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 a normalized 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 normalized_uri = html5lib_shim.convert_entities(value) # Nix backtick, space characters, and control characters normalized_uri = re.sub(r"[`\000-\040\177-\240\s]+", "", normalized_uri) # Remove REPLACEMENT characters normalized_uri = normalized_uri.replace("\ufffd", "") # Lowercase it--this breaks the value, but makes it easier to match # against normalized_uri = normalized_uri.lower() try: # Drop attributes with uri values that have protocols that aren't # allowed parsed = parse_shim.urlparse(normalized_uri) 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 normalized_uri.startswith("#"): return value # Handle protocols that urlparse doesn't recognize like "myprotocol" if ( ":" in normalized_uri and normalized_uri.split(":")[0] in allowed_protocols ): return value # If there's no protocol/scheme specified, then assume it's "http" or # "https" and see if that's allowed if "http" in allowed_protocols or "https" 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, "style"): if self.css_sanitizer: val = self.css_sanitizer.sanitize_css(val) else: # FIXME(willkg): if style is allowed, but no # css_sanitizer was set up, then this is probably a # mistake and we should raise an error here # # For now, we're going to set the value to "" because # there was no sanitizer set val = "" # At this point, we want to keep the attribute, so add it in attrs[namespaced_name] = val token["data"] = 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 = "{}:{}".format(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"] = "<{}{}>".format(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