Match The Regex CTF Walkthrough – Regex Pattern Challenge Solved

 MatchTheRegex

CTF Author: Sunday Jacob Nwanyim

Description

How about trying to match a regular expression

Hints: Access the webpage and try to match the regular expression associated with the text field.

So after reading this problem and hint it was very clear that we need to do something with input field and Regex, so I researched about Regex from Chatgpt.

This is the information provided by Chatgpt.

A regex (short for regular expression) is a sequence of characters that defines a search pattern. It is used to match, search, and manipulate text based on specific patterns. Regex is commonly used in programming, data validation, text processing, and search functions.

After this I visited the website.

After this I checked the source code and boom we got a piece of code which is returning the flag.

There’s are a our flag p…..F!?

From this it very cleared that we first character is p and fifth character is F and the flag will end with ! or ?

There are several methods for matching the regex pattern using console of developer’s tools or by sending an input script using burp suite.I asked for the script from chatgpt.

Script is: GET /flag?input=pabcdeF! HTTP/1.1

Host: example.com

I opened the burp suite and found a get request and sent it to the repeater.

And inserted the above script in get request.

And Boom here’s the flag:

Flag:picoCTF{succ3ssfully_matchtheregex_8ad436ed}

What I Learned

This challenge was a great introduction to several important concepts:

Regex Basics: Although this was a straightforward pattern match, it reinforced how regex works and why it is so useful for text manipulation.

Source Code Analysis: Always look to the source! Web challenges often conceal clues in comments, JavaScript, or HTML that aren't immediately apparent.

HTTP Request Manipulation: Manipulating requests with the use of Burp Suite is a fundamental web security skill. This challenge provided me with direct experience in constructing GET requests.

Begin with the source - Look at the page source, inspect network requests, and inspect JavaScript files

Know your tool - Whether regex, SQL, or some other technology, be sure you understand the fundamentals

Experiment with several methods - Don't become fixated on a single method; there are typically a few different ways to a web problem

Log your method - Documenting what you do helps when you're stuck

Final Thoughts

MatchTheRegex may be easy once you understand the answer, but it does teach core skills that are used in much harder difficulties. The mix of source code analysis, regex knowledge, and HTTP tampering gives a sound basis for web exploitation difficulties.

Final Thoughts

MatchTheRegex might seem straightforward once you know the solution, but it teaches fundamental skills that apply to much more complex challenges. The combination of source code analysis, regex understanding, and HTTP manipulation creates a solid foundation for web exploitation challenges.

Plus, there's something satisfying about seeing that flag pop up after connecting all the pieces together!

Challenge Source: picoCTF

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Happy hacking, and remember - the best way to learn cybersecurity is by getting your hands dirty with challenges like these!