MatchTheRegex

Author: Sunday Jacob Nwanyim | 100 points

Description

How about trying to match a regular expression

The website is running here.

Solution

For this challenge, we are given a simple submit box webpage.

input box

Upon entered a string of text into the box and clicking submit, we are greeted with a error window.

wrong match!

We can examine the source code by right clicking the page or by using (Crtl+U). From here we find the JavaScript hard-coded into the page.

<script>
	function send_request() {
		let val = document.getElementById("name").value;
		// ^p.....F!?
		fetch(`/flag?input=${val}`)
			.then(res => res.text())
			.then(res => {
				const res_json = JSON.parse(res);
				alert(res_json.flag)
				return false;
			})
		return false;
	}
</script>

We are given the regular expression we have to match in the comments of the JavaScript. Here we have to match ^p.....F!?, which obviously matches the name of the CTF: picoCTF.

picoCTF

flag

Flag

The flag is picoCTF{succ3ssfully_matchtheregex_f89ea585}