Flash CTF - Treasure Map
Web Exploitation — Difficulty ★☆☆
Challenge Brief
We're given a small pirate-themed web site called The Digital Buccaneer. Nothing in the main navigation mentions a flag, but the description hints that "every ship keeps a map of its territory" and nudges us toward looking for a sitemap file.
Our goal is simple: Find the hidden page that contains the flag.
Initial Recon
Open the root of the site in a browser (or with curl) and click around. Doing so, you'll find the following pages:
/– landing page/crew,/ship,/history– informational pages
Nothing stands out, so we move on to common "well-known" discovery files that sites often leave lying around. A quick word-list scan, (or manual guess), for sitemap.xml (as hinted many times on the website) pays off:
$ curl -s http://digitalbuccaneer.chals.mctf.io/sitemap.xml | head
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url>
<loc>http://digitalbuccaneer.chals.mctf.io/</loc>
Reading sitemap.xml
Scrolling a bit further we notice something juicy:
<!-- SECRET TREASURE LOCATION - Do not tell the crew! -->
<url>
<loc>http://digitalbuccaneer.chals.mctf.io/treasure-chamber</loc>
<lastmod>2024-01-15</lastmod>
<changefreq>never</changefreq>
<priority>0.9</priority>
</url>
The sitemap openly lists a treasure-chamber endpoint that is never linked from the UI.
Claiming the Treasure
Visit the URL we just found:
$ curl -s http://digitalbuccaneer.chals.mctf.io/treasure-chamber | grep -i metaCTF
MetaCTF{y0u_f0und_7h3_tr34sur3_m4p_4nd_g0t_7h3_f14g}
We've got the flag.
MetaCTF{x_marks_the_digital_spot_matey}
An Additional Solution: robots.txt
After solving the challenge we inspected another common file, robots.txt, and found it contains a comment that literally points to the sitemap:
User-agent: *
Allow: /# For those seeking treasure, check our sitemap!
Sitemap: http://digitalbuccaneer.chals.mctf.io/sitemap.xml
So there were actually two separate breadcrumbs:
- Blindly enumerating well-known files (
sitemap.xml). - Reading
robots.txt, which in turn advertises the sitemap location.
Either path leads to the same hidden endpoint.
