Fix JWT validation in Python and Flask
======================================

Verify every bearer token with PyJWT's jwt.decode(token, key,
algorithms=["RS256"], issuer=..., audience=..., leeway=30, options={"require":
["exp", "iss", "aud", "sub"]}), with the key from configuration. Never pass
verify_signature False, and never silence InvalidAudienceError with verify_aud
False: a token for another API or tenant must fail.

Page: https://softwaresecurity.com/fix/jwt-validation/python-flask/

What is in this archive
-----------------------
jwt-validation/python-flask/   the project: three implementations of the same code and one test suite
  impl/vulnerable.py   (vulnerable)
  impl/fixed.py   (fixed)
  impl/wrong.py   (a plausible fix that still fails)
run-all.mjs   runs the tests in all three modes and checks the results (Node.js only)
LICENSE-CODE.txt

Run it
------
  Tested with CPython 3.14.8. run-all.mjs needs Node.js 22 or later. Supported
  versions: https://softwaresecurity.com/fix/versions/

  From the jwt-validation/python-flask folder, install the dependencies once
  (this needs network access):

    python3 -m venv .venv
    .venv/bin/python -m pip install -r requirements.txt

  Then run the tests. IMPL chooses the implementation the tests load:

    # every test passes
    IMPL=fixed .venv/bin/python -m pytest
    # an exploit test fails
    IMPL=vulnerable .venv/bin/python -m pytest
    # a test fails
    IMPL=wrong .venv/bin/python -m pytest

  The JUnit report is written to reports/junit.xml. To run all three modes and
  check the results in one step, run the harness from this top folder (it needs
  only Node.js; --install runs the install step first):

    node run-all.mjs --install jwt-validation/python-flask
    node run-all.mjs jwt-validation/python-flask

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with python 3.14.8,
  flask 3.1.3, pyjwt 2.15.0, cryptography 50.0.2, pytest 9.1.1. Versions and
  results hold for that date: run the tests with your own versions before
  relying on the fix.

Licence
-------
  The code is MIT licensed (LICENSE-CODE.txt). The page text is CC BY 4.0.
