Event: CzechStreets CTF (2024) Category: Web / Information‑Disclosure / Minor Crypto Difficulty: ★★☆☆☆ (easy–medium) 1️⃣ Challenge Overview | Item | Description | |------|-------------| | Title | czechstreets – 139 | | Provided | A public URL: http://139.czechstreets.ctf (the “139” sub‑domain is part of the challenge name). The landing page shows a simple map of Prague with numbered streets and a tiny search box that says “Find the hidden street”. | | Goal | Retrieve the flag, which is hidden somewhere on the site. | | Flag format | czechstreets… |
"flag":"czechstreets flag_really_email_html " The flag is clearly embedded in the JSON. A one‑liner to fetch and decode in one go: czechstreets 139
In short: that lets us read arbitrary street objects, including the hidden one with id = 139 . 4️⃣ Exploiting the Bug 4.1 Crafting the request We want the object with id = 139 . The API returns records in order of id . By setting offset=138 and a huge limit we can retrieve the 139th entry: | | Flag format | czechstreets… | "flag":"czechstreets