Fix reflected XSS in XSS Reflected Low challenge

[r1kka6]

Summary

• encode the reflected name parameter before rendering it in the low-security XSS page
• keep the change scoped to vulnerabilities/xss_r/source/low.php

Root cause

The low-security reflected XSS handler concatenated the attacker-controlled name query parameter directly into HTML output, allowing script markup to be interpreted by the browser.

Validation

• docker run --rm -v "$PWD:/work" -w /work php:8.3-cli php -l vulnerabilities/xss_r/source/low.php
• docker run --rm -v "$PWD:/work" -w /work php:8.3-cli php -r '$_GET["name"]="<script>alert(1)</script>"; $html=""; include "vulnerabilities/xss_r/source/low.php"; echo $html;' -> <pre>Hello &lt;script&gt;alert(1)&lt;/script&gt;</pre>
• docker run --rm -v "$PWD:/work" -w /work php:8.3-cli php -r '$_GET["name"]="Alice"; $html=""; include "vulnerabilities/xss_r/source/low.php"; echo $html;' -> <pre>Hello Alice</pre>
• docker build -t dvwa-ctf-xss-reflected-low .
• Built image + MariaDB runtime: /vulnerabilities/xss_r/?name=%3Cscript%3Ealert%281%29%3C%2Fscript%3E -> <pre>Hello &lt;script&gt;alert(1)&lt;/script&gt;</pre>
• Built image + MariaDB runtime: /vulnerabilities/xss_r/?name=Alice -> <pre>Hello Alice</pre>