CTF-Writeups

You are Chris Wong, you have a mission to win the game and redeem the free meal. Try to get over 300 score. Your flag will appears in scoreboard.php. Intercept the score update HTTP POST Request: Observe that it includes a payload with parameters score and hash. Modify the Score and Resend: Change the score value in the intercepted request and resend it. The server responds with “Invalid hash,” it indicates that the score is part of the hash calculation. Identify the Hashing Algorithm: ...

I made a simple webpage that checks whether the flag is correct… Wait, where are the flag-checking functions? Inspect the Page: Upon inspecting the webpage, there’s an empty or seemingly empty JavaScript block. There’s also a link to an X post: Link. This post introduces the concept of hiding JavaScript code using the Hangul Filler character (\\u3164). Invisible Code Concept: The JavaScript code relies on the \\u3164 character, which is an invisible Hangul Filler character, to hide the flag-checking logic. The with block is used to access properties formed by sequences of \\u3164. The length of these sequences represents the binary value of the ASCII character. Proxy and Property Access: ...