PortSwigger - Reflexted XSS in canonical link tag

Jun Takemura · April 30, 2025

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Task

This lab reflects user input in a canonical link tag and escapes angle brackets.

To solve the lab, perform a cross-site scripting attack on the home page that injects an attribute that calls the alert function.

To assist with your exploit, you can assume that the simulated user will press the following key combinations:

  • ALT+SHIFT+X
  • CTRL+ALT+X
  • Alt+X

Please note that the intended solution to this lab is only possible in Chrome.

Attempt

The website reflects a request url directly into the href attribute of the <link rel="canonical"> tag without escaping.

So you can use a payload like this:

https://https://0aa1003c0440c57680f20d8600820079.web-security-academy.net/?%27accesskey=%27x%27onclick=%27alert(1)

Here acesskey attribute specifies a shortcut key. In Chrome on linux, you can press Alt+X and it will trigger alert(1).

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