There is a Cross-Site-Scripting vulnerability during account creation when redirecting after the account has been successfully created.
Exploitation requires the user to initiate the account creation process with a maliciously crafted link, and then finalize the signup process. Because of this, it can only target newly created (and thus unprivileged) Indico users so the benefits of exploiting it are very limited.
Patches
You should to update to Indico 3.3.4 as soon as possible.
See the docs for instructions on how to update.
Workarounds
If you build the Indico package yourself and cannot upgrade for some reason, you can simply update the flask-multipass dependency to >=0.5.5 which fixes the vulnerability. You would do that by editing requirements.txt before building the package (see commit 7dcb573837), or possibly cherry-picking that particular commit.
Otherwise you could configure your web server to disallow requests containing a query string with a parameter that starts with javascript:
For more information
If you have any questions or comments about this advisory: