[Bug] TAXII 2.0 Server Has Been Retired

Expected Behavior

Using the exporters such as Excel or SVG using the default taxii source should retrieve the proper data and produce the expected exported output.

Actual Behavior

navlayers.ToExcel() hangs because the server "https://cti-taxii.mitre.org/taxii" has been retired as of December 18th blog link

Steps to Reproduce the Problem

For example: calling the following function navlayers.ToExcel(domain="enterprise", source="taxii") just hangs

Possible Solution

Migrating to the TAXII 2.1 server. The problem exists in navlayers/exporters/matrix_gen.py in the __init__ method of the MatrixGen class.

class MatrixGen:
    """A MatrixGen object."""

    def __init__(self, source="taxii", resource=None, domain="enterprise"):
        """Initialize - Creates a matrix generator object.

        :param source: Source to utilize (taxii, remote, or local)
        :param resource: string path to local cache of stix data (local) or url of an ATT&CK Workbench (remote)
        """
        self.convert_data = {}
        self.collections = dict()
        if source.lower() not in ["taxii", "local", "remote", "memorystore"]:
            logger.error(
                f"Unable to generate matrix, source {source} is not one of [taxii | remote | local | memorystore]"
            )
            raise ValueError

        if source.lower() == "taxii":
            self.server = Server("https://cti-taxii.mitre.org/taxii")
            self.api_root = self.server.api_roots[0]
            for collection in self.api_root.collections:
                if collection.title != "PRE-ATT&CK":
                    tc = Collection("https://cti-taxii.mitre.org/stix/collections/" + collection.id)
                    self.collections[collection.title.split(" ")[0].lower()] = TAXIICollectionSource(tc)

Start in navlayers/exporters/matrix_gen.py, specifically the MatrixGen.init method and its TAXII source setup. Reproduce the hang with navlayers.ToExcel(domain="enterprise", source="taxii") and verify that the Excel and SVG exporters retrieve data and produce their expected output without hanging.