FlowStrider

FlowStrider is an architectural threat modeling tool designed to support the identification, mitigation, documentation, and management of threats in a given software system.

Why use FlowStrider?

• Enables continuous threat modeling

• Automates key parts of the threat modeling process

• Follows a practice-oriented workflow inspired by real-world use cases

• Easily integrates into CI/CD pipelines

• Programming-language agnostic

• Fully scriptable and extensible

Features

🛠 Refine System Representation: Assists in adding relevant metadata to the system representation to enhance the quality of threat modeling.

🛡 Identification of Threats: Uses three built-in rule sets to identify threats based on the system representation.

📊 Reporting: Supports the documentation and management of identified threats in a structured report.

Documentation

For the full documentation of the FlowStrider tool, please visit the GitLab page or build the documentation locally (using tox -e docs).

Installation

As a prerequisite, FlowStrider requires Python (tested with versions 3.10 and 3.12) and Graphviz, which can be installed via apt install graphviz or as described on their website.

Install the tool directly using pip install flowstrider or clone this repository and install it (using git clone and pip install). Dependencies are handled automatically during the installation process as defined in setup.cfg.

Usage

1. Threat elicitation

FlowStrider takes as input a data-flow diagram (DFD) expressed as a json file that follows FlowStrider’s DFD format (example below). This data-flow diagram is then used to model potential threats.

flowstrider elicit dataflow_diagram.json [--output-path *output-file-path*]
                                         [--management-path *management-file-path*]
                                         [--fail-on-threat (off|undecided|todo|all)]
                                         [--out-lang (en|de)]

The results can be saved as a PDF file if the [--output-path] is set. The PDF includes a visual representation of the system generated with GraphViz and the details about the modeled threats also seen in the console.

The [--management-path] gives the path to a json file where information about the management state of each existing threat can be modified. If the file doesn’t exist yet, it will be created.

If [--fail-on-threat] (default=off) is set to off, the tool will not fail if it finds threats. If set to other options, the tool will fail if there is a threat with an unsufficient management state to explain its presence with the set fail option.

By default, each found threat is asigned the management state Undecided. The management state can be modified in the management file indicated by the [--management-path] option. There are seven different states each threat can take on as seen in the left column in the table below. The table also shows which state will fail the tool if run with a specific option for the [--fail-on-threat] argument.

	off	undecided	todo	all
Undecided	pass	fail	fail	fail
Delegate	pass	pass	fail	fail
Mitigate	pass	pass	fail	fail
Avoid	pass	pass	fail	fail
Accept	pass	pass	pass	fail
Delegated	pass	pass	pass	fail
Mitigated	pass	pass	pass	fail

The parameter [--out-lang] (default=en) denotes the output language used for the threats and the report.

2. Missing Metadata overview

The tool relies on metadata (stored in the attributes property of the nodes and edges) to accurately elicit threats. An .xlsx file can be generated to get an overview of the attributes stored in the metadata, as well as any relevant attributes that are missing.

flowstrider metadata dataflow_diagram.json metadata_overview.xlsx [--out-lang (en|de)]

The parameter [--out-lang] (default=en) denotes the output language used for the metadata xlsx file.

3. Updating Metadata using the xlsx overview

After filling out the missing metadata in the xlsx file, that file can be used to update the existing json file of the data-flow diagram. The modified and added attributes are then being updated as metadata to the nodes and edges of the diagram.

flowstrider update dataflow_diagram.json metadata_overview.xlsx

Tip:

For a more in depth workflow take a look at the section *Detailed Workflow*.

Creating a System Representation

FlowStrider accepts a system representation as a data-flow diagram (DFD) in its json-based FlowStrider DFD format. See the Data-Flow Diagram section in the documentation for more information on how do define elements and assign attributes. In the tags of the dfd at the bottom of the json file, one can define the rule sets the tool is checking against. See the Rule Sets section on the different rule sets.

Here is a minimal example of such a data-flow diagram in .json:

{
  "dfd": {
    "id": "Example",
    "nodes": {
      "node1": {
        "id": "node1",
        "name": "User",
        "tags": [
          "STRIDE:Interactor"
        ],
        "attributes": {}
      },
      "node2": {
        "id": "node2",
        "name": "Application",
        "tags": [
          "STRIDE:Process"
        ],
        "attributes": {}
      }
    },
    "edges": {
      "edge1": {
        "id": "edge1",
        "source_id": "node1",
        "sink_id": "node2",
        "name": "http_request",
        "tags": [
          "STRIDE:Dataflow"
        ],
        "attributes": {}
      }
    },
    "clusters": {
      "cluster1":{
        "id": "cluster1",
        "node_ids": [
          "node2"
        ],
        "name": "Internet",
        "tags": [
          "STRIDE:TrustBoundary"
        ],
        "attributes": {}
      }
    },
    "name": "",
    "tags": [
      "bsi_rules"
    ],
    "attributes": {}
  }
}

Legal

All files in this repository fall under the stated license in LICENSE.txt. The full licensing terms of used dependencies can be found in LICENSE-3RD-PARTY.txt

Making Changes & Contributing

Please make sure to read CONTRIBUTING.rst and follow the preparations before making any changes to the project.

Cite FlowStrider

The paper “FlowStrider: Low-friction Continuous Threat Modeling” was accepted at the Tool Track of ASE25.

Funding

This work was done as part of the AVATAR competence cluster, funded by the Federal Ministry of Research, Technology and Space (funding code: 16KISA012).