Vulnerability Instance

urllib3 does not control redirects in browsers and Node.js
urllib3 [supports](https://urllib3.readthedocs.io/en/2.4.0/reference/contrib/emscripten.html) being used in a Pyodide runtime utilizing the [JavaScript Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) or falling back on [XMLHttpRequest](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest). This means you can use Python libraries to make HTTP requests from your browser or Node.js. Additionally, urllib3 provides [a mechanism](https://urllib3.readthedocs.io/en/2.4.0/user-guide.html#retrying-requests) to control redirects.

However, the `retries` and `redirect` parameters are ignored with Pyodide; the runtime itself determines redirect behavior.


## Affected usages

Any code which relies on urllib3 to control the number of redirects for an HTTP request in a Pyodide runtime.


## Impact

Redirects are often used to exploit SSRF vulnerabilities. An application attempting to mitigate SSRF or open redirect vulnerabilities by disabling redirects may remain vulnerable if a Pyodide runtime redirect mechanism is unsuitable.


## Remediation

If you use urllib3 in Node.js, upgrade to a patched version of urllib3.

Unfortunately, browsers provide no suitable way which urllib3 can use: `XMLHttpRequest` provides no control over redirects, the Fetch API returns `opaqueredirect` responses lacking data when redirects are controlled manually. Expect default browser behavior for redirects.