Specifying additional remote flow sources for JavaScript

As mentioned in the :doc:`Data flow cheat sheet for JavaScript <data-flow-cheat-sheet-for-javascript>`, the CodeQL libraries for JavaScript

provide a class `RemoteFlowSource <https://codeql.github.com/codeql-standard-libraries/javascript/semmle/javascript/security/dataflow/RemoteFlowSources.qll/type.RemoteFlowSources$RemoteFlowSource.html>`__ to represent sources of untrusted user input, sometimes also referred to as `remote flow

sources`.

To model a new source of untrusted input, such as a previously unmodelled library API, you can

define a subclass of ``RemoteFlowSource`` that covers all uses of that API. All standard analyses

will then automatically pick up this new source of remote flow.

However, this approach requires writing QL code and adding it to the standard library, which is not

always easy to do. Instead, you can also add a JSON file describing custom sources of untrusted

input to your code base and have it picked up without needing to modify the standard library. This

JSON file can be hand-written or generated by another tool, but note that these customizations

are specific to the code base containing the JSON file. To use them in other code bases, you need

to copy over the JSON file.

Specification format

The JSON file must be called ``codeql-javascript-remote-flow-sources.json`` (case-sensitive) and

can be located anywhere in your code base. It should consist of a single JSON object. The property

names of this object are interpreted as `source types`. The values they map to should be arrays of

strings. Each string should be of the form ``window.props``, where ``props`` is a sequence of one

or more property names separated by dots, specifying that any value reachable from the global window

object by this sequence of property names should be considered as untrusted user input of the

associated source type.

Example

As an example, consider the following specification:

.. code-block:: json

It declares that the contents of global variable ``dob``, as well as the contents of properties

``name`` and ``address`` of global variable ``user``, should be considered as remote flow sources,

with source type "user input".