Fix weak password hashing in Python and Flask
=============================================

Use argon2-cffi's PasswordHasher with explicit parameters at or above OWASP's
minimum, PasswordHasher(time_cost=2, memory_cost=19456, parallelism=1), and
store ph.hash(password). On login, check legacy SHA-256 rows with
hmac.compare_digest and the rest with ph.verify(). After a success, rehash
when the row is legacy or ph.check_needs_rehash() is true, and save it with a
compare-and-swap.

Page: https://softwaresecurity.com/fix/password-hashing/python-flask/

What is in this archive
-----------------------
password-hashing/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 password-hashing/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 password-hashing/python-flask
    node run-all.mjs password-hashing/python-flask

Verified
--------
  11 October 2026, with python 3.14.8, pip 26.2.1. 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.
