407 lines
13 KiB
Python
407 lines
13 KiB
Python
"""Utility functions and classes for the STIX2 library."""
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from collections import Mapping
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import copy
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import datetime as dt
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import json
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from dateutil import parser
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import pytz
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import stix2.base
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from .exceptions import (
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InvalidValueError, RevokeError, UnmodifiablePropertyError,
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)
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# Sentinel value for properties that should be set to the current time.
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# We can't use the standard 'default' approach, since if there are multiple
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# timestamps in a single object, the timestamps will vary by a few microseconds.
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NOW = object()
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# STIX object properties that cannot be modified
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STIX_UNMOD_PROPERTIES = ['created', 'created_by_ref', 'id', 'type']
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TYPE_REGEX = r'^\-?[a-z0-9]+(-[a-z0-9]+)*\-?$'
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class STIXdatetime(dt.datetime):
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def __new__(cls, *args, **kwargs):
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precision = kwargs.pop('precision', None)
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if isinstance(args[0], dt.datetime): # Allow passing in a datetime object
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dttm = args[0]
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args = (
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dttm.year, dttm.month, dttm.day, dttm.hour, dttm.minute,
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dttm.second, dttm.microsecond, dttm.tzinfo,
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)
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# self will be an instance of STIXdatetime, not dt.datetime
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self = dt.datetime.__new__(cls, *args, **kwargs)
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self.precision = precision
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return self
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def __repr__(self):
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return "'%s'" % format_datetime(self)
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def deduplicate(stix_obj_list):
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"""Deduplicate a list of STIX objects to a unique set.
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Reduces a set of STIX objects to unique set by looking
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at 'id' and 'modified' fields - as a unique object version
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is determined by the combination of those fields
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Note: Be aware, as can be seen in the implementation
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of deduplicate(),that if the "stix_obj_list" argument has
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multiple STIX objects of the same version, the last object
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version found in the list will be the one that is returned.
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Args:
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stix_obj_list (list): list of STIX objects (dicts)
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Returns:
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A list with a unique set of the passed list of STIX objects.
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"""
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unique_objs = {}
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for obj in stix_obj_list:
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try:
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unique_objs[(obj['id'], obj['modified'])] = obj
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except KeyError:
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# Handle objects with no `modified` property, e.g. marking-definition
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unique_objs[(obj['id'], obj['created'])] = obj
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return list(unique_objs.values())
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def get_timestamp():
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"""Return a STIX timestamp of the current date and time."""
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return STIXdatetime.now(tz=pytz.UTC)
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def format_datetime(dttm):
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"""Convert a datetime object into a valid STIX timestamp string.
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1. Convert to timezone-aware
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2. Convert to UTC
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3. Format in ISO format
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4. Ensure correct precision
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a. Add subsecond value if non-zero and precision not defined
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5. Add "Z"
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"""
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if dttm.tzinfo is None or dttm.tzinfo.utcoffset(dttm) is None:
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# dttm is timezone-naive; assume UTC
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zoned = pytz.utc.localize(dttm)
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else:
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zoned = dttm.astimezone(pytz.utc)
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ts = zoned.strftime('%Y-%m-%dT%H:%M:%S')
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ms = zoned.strftime('%f')
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precision = getattr(dttm, 'precision', None)
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if precision == 'second':
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pass # Already precise to the second
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elif precision == 'millisecond':
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ts = ts + '.' + ms[:3]
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elif zoned.microsecond > 0:
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ts = ts + '.' + ms.rstrip('0')
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return ts + 'Z'
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def parse_into_datetime(value, precision=None):
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"""Parse a value into a valid STIX timestamp object.
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"""
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if isinstance(value, dt.date):
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if hasattr(value, 'hour'):
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ts = value
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else:
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# Add a time component
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ts = dt.datetime.combine(value, dt.time(0, 0, tzinfo=pytz.utc))
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else:
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# value isn't a date or datetime object so assume it's a string
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try:
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parsed = parser.parse(value)
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except (TypeError, ValueError):
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# Unknown format
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raise ValueError(
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"must be a datetime object, date object, or "
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"timestamp string in a recognizable format.",
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)
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if parsed.tzinfo:
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ts = parsed.astimezone(pytz.utc)
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else:
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# Doesn't have timezone info in the string; assume UTC
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ts = pytz.utc.localize(parsed)
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# Ensure correct precision
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if not precision:
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return STIXdatetime(ts, precision=precision)
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ms = ts.microsecond
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if precision == 'second':
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ts = ts.replace(microsecond=0)
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elif precision == 'millisecond':
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ms_len = len(str(ms))
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if ms_len > 3:
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# Truncate to millisecond precision
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factor = 10 ** (ms_len - 3)
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ts = ts.replace(microsecond=(ts.microsecond // factor) * factor)
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else:
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ts = ts.replace(microsecond=0)
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return STIXdatetime(ts, precision=precision)
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def _get_dict(data):
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"""Return data as a dictionary.
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Input can be a dictionary, string, or file-like object.
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"""
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if type(data) is dict:
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return data
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else:
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try:
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return json.loads(data)
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except TypeError:
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pass
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try:
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return json.load(data)
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except AttributeError:
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pass
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try:
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return dict(data)
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except (ValueError, TypeError):
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raise ValueError("Cannot convert '%s' to dictionary." % str(data))
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def _find(seq, val):
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"""
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Search sequence 'seq' for val. This behaves like str.find(): if not found,
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-1 is returned instead of throwing an exception.
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Args:
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seq: The sequence to search
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val: The value to search for
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Returns:
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int: The index of the value if found, or -1 if not found
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"""
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try:
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return seq.index(val)
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except ValueError:
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return -1
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def _find_property_in_seq(seq, search_key, search_value):
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"""
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Helper for find_property_index(): search for the property in all elements
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of the given sequence.
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Args:
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seq: The sequence
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search_key: Property name to find
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search_value: Property value to find
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Returns:
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int: A property index, or -1 if the property was not found
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"""
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idx = -1
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for elem in seq:
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idx = find_property_index(elem, search_key, search_value)
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if idx >= 0:
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break
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return idx
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def find_property_index(obj, search_key, search_value):
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"""
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Search (recursively) for the given key and value in the given object.
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Return an index for the key, relative to whatever object it's found in.
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Args:
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obj: The object to search (list, dict, or stix object)
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search_key: A search key
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search_value: A search value
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Returns:
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int: An index; -1 if the key and value aren't found
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"""
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from .base import _STIXBase
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# Special-case keys which are numbers-as-strings, e.g. for cyber-observable
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# mappings. Use the int value of the key as the index.
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if search_key.isdigit():
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return int(search_key)
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if isinstance(obj, _STIXBase):
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if search_key in obj and obj[search_key] == search_value:
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idx = _find(obj.object_properties(), search_key)
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else:
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idx = _find_property_in_seq(obj.values(), search_key, search_value)
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elif isinstance(obj, dict):
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if search_key in obj and obj[search_key] == search_value:
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idx = _find(sorted(obj), search_key)
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else:
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idx = _find_property_in_seq(obj.values(), search_key, search_value)
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elif isinstance(obj, list):
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idx = _find_property_in_seq(obj, search_key, search_value)
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else:
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# Don't know how to search this type
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idx = -1
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return idx
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def new_version(data, **kwargs):
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"""Create a new version of a STIX object, by modifying properties and
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updating the ``modified`` property.
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"""
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if not isinstance(data, Mapping):
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raise ValueError(
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"cannot create new version of object of this type! "
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"Try a dictionary or instance of an SDO or SRO class.",
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)
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unchangable_properties = []
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if data.get('revoked'):
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raise RevokeError("new_version")
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try:
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new_obj_inner = copy.deepcopy(data._inner)
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except AttributeError:
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new_obj_inner = copy.deepcopy(data)
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properties_to_change = kwargs.keys()
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# Make sure certain properties aren't trying to change
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for prop in STIX_UNMOD_PROPERTIES:
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if prop in properties_to_change:
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unchangable_properties.append(prop)
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if unchangable_properties:
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raise UnmodifiablePropertyError(unchangable_properties)
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cls = type(data)
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if 'modified' not in kwargs:
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kwargs['modified'] = get_timestamp()
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elif 'modified' in data:
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old_modified_property = parse_into_datetime(data.get('modified'), precision='millisecond')
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new_modified_property = parse_into_datetime(kwargs['modified'], precision='millisecond')
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if new_modified_property <= old_modified_property:
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raise InvalidValueError(
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cls, 'modified',
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"The new modified datetime cannot be before than or equal to the current modified datetime."
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"It cannot be equal, as according to STIX 2 specification, objects that are different "
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"but have the same id and modified timestamp do not have defined consumer behavior.",
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)
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new_obj_inner.update(kwargs)
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# Exclude properties with a value of 'None' in case data is not an instance of a _STIXBase subclass
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return cls(**{k: v for k, v in new_obj_inner.items() if v is not None})
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def revoke(data):
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"""Revoke a STIX object.
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Returns:
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A new version of the object with ``revoked`` set to ``True``.
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"""
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if not isinstance(data, Mapping):
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raise ValueError(
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"cannot revoke object of this type! Try a dictionary "
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"or instance of an SDO or SRO class.",
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)
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if data.get('revoked'):
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raise RevokeError("revoke")
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return new_version(data, revoked=True, allow_custom=True)
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def get_class_hierarchy_names(obj):
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"""Given an object, return the names of the class hierarchy."""
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names = []
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for cls in obj.__class__.__mro__:
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names.append(cls.__name__)
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return names
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def remove_custom_stix(stix_obj):
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"""Remove any custom STIX objects or properties.
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Warnings:
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This function is a best effort utility, in that it will remove custom
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objects and properties based on the type names; i.e. if "x-" prefixes
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object types, and "x\\_" prefixes property types. According to the
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STIX2 spec, those naming conventions are a SHOULDs not MUSTs, meaning
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that valid custom STIX content may ignore those conventions and in
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effect render this utility function invalid when used on that STIX
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content.
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Args:
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stix_obj (dict OR python-stix obj): a single python-stix object
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or dict of a STIX object
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Returns:
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A new version of the object with any custom content removed
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"""
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if stix_obj['type'].startswith('x-'):
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# if entire object is custom, discard
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return None
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custom_props = []
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for prop in stix_obj.items():
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if prop[0].startswith('x_'):
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# for every custom property, record it and set value to None
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# (so we can pass it to new_version() and it will be dropped)
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custom_props.append((prop[0], None))
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if custom_props:
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# obtain set of object properties that can be transferred
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# to a new object version. This is 1)custom props with their
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# values set to None, and 2)any properties left that are not
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# unmodifiable STIX properties or the "modified" property
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# set of properties that are not supplied to new_version()
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# to be used for updating properties. This includes unmodifiable
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# properties (properties that new_version() just re-uses from the
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# existing STIX object) and the "modified" property. We dont supply the
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# "modified" property so that new_version() creates a new datetime
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# value for this property
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non_supplied_props = STIX_UNMOD_PROPERTIES + ['modified']
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props = [(prop, stix_obj[prop]) for prop in stix_obj if prop not in non_supplied_props]
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# add to set the custom properties we want to get rid of (with their value=None)
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props.extend(custom_props)
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new_obj = new_version(stix_obj, **(dict(props)))
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while parse_into_datetime(new_obj['modified']) == parse_into_datetime(stix_obj['modified']):
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# Prevents bug when fast computation allows multiple STIX object
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# versions to be created in single unit of time
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new_obj = new_version(stix_obj, **(dict(props)))
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return new_obj
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else:
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return stix_obj
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def get_type_from_id(stix_id):
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return stix_id.split('--', 1)[0]
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def is_marking(obj_or_id):
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"""Determines whether the given object or object ID is/is for a marking
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definition.
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:param obj_or_id: A STIX object or object ID as a string.
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:return: True if a marking definition, False otherwise.
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"""
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if isinstance(obj_or_id, (stix2.base._STIXBase, dict)):
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result = obj_or_id["type"] == "marking-definition"
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else:
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# it's a string ID
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result = obj_or_id.startswith("marking-definition--")
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return result
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