Authorization disclaimer. This walkthrough is limited to the intentionally vulnerable PortSwigger Web Security Academy lab linked below. Test only systems you own or are explicitly authorized to assess.

Overview

This lab isolates Unencoded reflected HTML. The search parameter is inserted directly into HTML body text without encoding <, >, quotes, or ampersands. Because the browser receives attacker-controlled markup in an HTML text context, it creates a script element rather than displaying the characters.

Lab objective/setup

Open the Academy exercise at the reserved lab URL and work only in that disposable environment. The required proof is specific: Submitting the search URL executes alert(1) and solves the lab.

What I observed

The search parameter is inserted directly into HTML body text without encoding <, >, quotes, or ampersands. Because the browser receives attacker-controlled markup in an HTML text context, it creates a script element rather than displaying the characters.

Academy objective describing a simple reflected XSS flaw in the blog search function.
Academy objective describing a simple reflected XSS flaw in the blog search function.

Why it is vulnerable

The application applies protection for the wrong parser or omits a control at the decisive boundary. In this case, the search parameter is inserted directly into HTML body text without encoding <, >, quotes, or ampersands. Browser parsing therefore preserves the attacker-controlled behavior instead of reducing the value to inert text or a safe URL.

Walkthrough in the authorized PortSwigger lab

First reproduce the recorded page or request and inspect the exact reflected, stored, or DOM-generated context described above. Then supply the following lab payload as data, not as active markup in this article:

1
`&lt;script&gt;alert(1)&lt;/script&gt;`

Because the browser receives attacker-controlled markup in an HTML text context, it creates a script element rather than displaying the characters.

Search page with the encoded script test entered in the query field before submission to the unencoded HTML text context.
Search page with the encoded script test entered in the query field before submission to the unencoded HTML text context.
Browser alert dialog showing `1` after the reflected script element is parsed and executed.
Browser alert dialog showing `1` after the reflected script element is parsed and executed.

Verification

Submitting the search URL executes alert(1) and solves the lab. This distinguishes execution from a payload merely appearing in source or being stored without reaching the required event or sink.

Impact and defensive lesson

In a real application, equivalent XSS could act with the victim’s same-origin privileges, expose readable data, or perform authenticated actions. Fix the data flow at its context: use text-only DOM APIs, JavaScript- or attribute-aware encoding, strict URL-scheme allowlists, and maintained sanitization where HTML is unavoidable. HttpOnly cookies and a restrictive CSP reduce consequences but do not repair the injection flaw.

References