Indico has a Cross-Site-Scripting during account creation

Vulnerability Description

Indico is an event management system that uses Flask-Multipass, a multi-backend authentication system for Flask. In Indico prior to version 3.3.4, corresponding to Flask-Multipass prior to version 0.5.5, there is a Cross-Site-Scripting vulnerability during account creation when redirecting to the `next` URL. Exploitation requires initiating the account creation process with a maliciously crafted link, and then finalizing the signup process. Because of this, it can only target newly created (and thus unprivileged) Indico users. Indico 3.3.4 upgrades the dependency on Flask-Multipass to version 0.5.5, which fixes the issue. Those who build the Indico package themselves and cannot upgrade can update the `flask-multipass` dependency to `>=0.5.5` which fixes the vulnerability. Otherwise one could configure one's web server to disallow requests containing a query string with a `next` parameter that starts with `javascript:`.

References

• https://github.com/indico/indico/security/advisories/GHSA-rrqf-w74j-24ff
• https://github.com/indico/flask-multipass/commit/0bdcf656d469e5f675cb56fd644d82fea3a97c2a
• https://github.com/indico/indico/commit/7dcb573837b9fd09d95f74d1baeae225b164cc8f
• https://github.com/indico/indico/releases/tag/v3.3.4