Fix XSS in TypeScript and Next.js
=================================

Render user text as React children and attributes, which React escapes, and
keep it out of dangerouslySetInnerHTML; if a field must carry HTML, sanitize
it with DOMPurify first. In JSON-LD or any inline script, replace every < with
\u003c after JSON.stringify. Link a website only when URL.parse gives http or
https.

Page: https://softwaresecurity.com/fix/xss/typescript-nextjs/

What is in this archive
-----------------------
xss/typescript-nextjs/   the project: three implementations of the same code and one test suite
  lib/impl/vulnerable.tsx   (vulnerable)
  lib/impl/fixed.tsx   (fixed)
  lib/impl/wrong.tsx   (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 Node.js 26.11.1; package.json allows Node.js ^22.23.2 || ^24.18.1
  || >=26.5.1. run-all.mjs needs Node.js 22 or later. Supported versions:
  https://softwaresecurity.com/fix/versions/

  From the xss/typescript-nextjs folder, install the dependencies once (this
  needs network access):

    npm ci

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

    # every test passes
    IMPL=fixed npm test --silent
    # an exploit test fails
    IMPL=vulnerable npm test --silent
    # a test fails
    IMPL=wrong npm test --silent

  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 xss/typescript-nextjs
    node run-all.mjs xss/typescript-nextjs

Verified
--------
  11 October 2026 on macOS 27.0 (Darwin 27.0.0, arm64), with node 26.11.1, npm
  11.20.0, next 16.4.0, react 19.3.0, parse5 8.0.1, vitest 5.0.3 (Vite 8.3.4),
  typescript 6.0.3, semgrep 1.180.0. 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.
