Jupyter Server has an open redirection vulnerability in `next` query parameter

Summary

The ?next=... URL query parameter has an open redirection vulnerability. In jupyter_server<=2.17.0, this URL query parameter allows redirection to arbitrary external domains, which can be exploited to facilitate phishing attacks on server users.

Details

The vulnerability is caused by insufficient validation in the LoginFormHandler._redirect_safe() method.

• Source code reference: https://github.com/jupyter-server/jupyter_server/blob/987ebdd5e188cdc49751b01a0d6782d686492a53/jupyter_server/auth/login.py#L33-L76

This vulnerability was originally reported by Noriaki Iwasaki. All discovery credit goes to them.

PoC

1. Navigate to http://localhost:8888/login?next=///google.com
2. Observe that the user is redirected to google.com despite it being an external domain.

The external domain passed in the ?next parameter may be replaced with a malicious lookalike to facilitate phishing attacks. Jupyter Server deployments served on a public domain are especially vulnerable, as prod.company.com may be redirected to a look-alike URL such as prod.company.dev.

Impact

This vulnerability affects all users, especially enterprise users who work with sensitive/confidential data.

Patches

Jupyter Server 2.18+

Workaround

None.