Summary

A user with the editmyprivateinfo right or who can otherwise change their name can XSS themselves by setting their "real name" to an XSS payload.

Details

Here's the offending line:

This was introduced in 717d16a

PoC

1. Login
2. Go to Special:Preferences
3. Set the real name field to a string like <script>alert("Admin with a propensity for self-XSSes")</script>
4. Save your settings and use Citizen if it's not being used already

Impact

Any user who can change their name (whether it's through the editmyprivateinfo right or through other means) can add XSS payloads that trigger for themselves only.