MantisBT: Reflected XSS in admin/install.php

Summary

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 print_test_result(). 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 <meta> 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/0f32ceabadc745239754962df91a51d5d51e3fd7 - https://github.com/mantisbt/mantisbt/commit/f2191a0d8ce438bf74171d496cf721dae025a5c0

### Workarounds Remove the `/admin` directory, as [recommended in the Admin Guide](https://mantisbt.org/docs/master/en-US/Admin_Guide/html-desktop/#admin.install.postcommon)

### Resources - https://mantisbt.org/bugs/view.php?id=37103 - related advisory [GHSA-vcrw-4xvv-jh49](https://github.com/mantisbt/mantisbt/security/advisories/GHSA-vcrw-4xvv-jh49)

### Credits McCaulay Hudson (@_McCaulay) of watchTowr