Fix XPath injection in Python and Flask
=======================================

Bind the input as XPath variables, never splice it into the expression. lxml's
doc.xpath("//employee[name=$n and role=$r]/title/text()", n=name, r=role)
matches the values as data, so quotes and operators in them are literal.
Parameterize every field, not just the obvious one, and keep secret nodes out
of what the query selects.

Page: https://softwaresecurity.com/fix/xpath-injection/python-flask/

What is in this archive
-----------------------
xpath-injection/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 xpath-injection/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 xpath-injection/python-flask
    node run-all.mjs xpath-injection/python-flask

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with python 3.14.8, pip
  26.2.1, flask 3.1.3, lxml 6.1.3, 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.
