MantisBT: Reflected XSS in admin/install.php via unescaped printf

MantisBT 2.28.3 and earlier contains six reflected XSS injection points in /admin/install.php. User-supplied parameters are echoed into HTML without escaping via an unescaped printf format string. No authentication is required.

A Content Security Policy (script-src 'self') prevents inline JavaScript execution, but the CSP is missing a form-action directive, allowing exploitation via credential-phishing form injection and open redirects.

### Impact - Credential phishing: Attacker crafts a URL that renders a fake login form on the real MantisBT admin page. Admin credentials are submitted to an attacker-controlled server. - Open redirect: Victim is silently redirected to a phishing or malware site. - UI manipulation: CSS injection can hide legitimate page content and overlay attacker-controlled HTML, enabling social engineering.

### Patches - https://github.com/mantisbt/mantisbt/commit/297773fbb238c39a153bd888431b41a176132098

Workarounds

Remove the /admin directory, as recommended in the Admin Guide

### Resources - https://mantisbt.org/bugs/view.php?id=37103 - related advisory GHSA-77x8-3v3h-hrhv

Credits

McCaulay Hudson (@_McCaulay) of watchTowr