PicoCTF 2017 – Special Agent User #appsec #infosec #forensics

Another day, another challenge.

Today’s blog post we will solving the “Special Agent User” challenge in the PicoCTF.

Let’s get started.

Clicking on the challenge we see:

We have another pcap (packet capture file) and we need to find the User Agent. OK. Sounds plausible. Let’s look at the hints.

There’s a link that discuss more about user-agents. Let’s go to that link.

Opening that link we see the following:

The web page explains the different components of the User-String. This will be useful.

Opening the packet capture file we notice the usual stuff UDP, and ICMP packets. And like with the first “Digital Camouflage” challenge we can ignore this.

User-Agent strings are found in HTTP requests. We need to look at packet captures for just HTTP requests.

Doing this we see a packet that’s piqued our interest…

On packet 80 (GET / HTTP/1.1) we’ll do a right click, Follow, HTTP stream.

Doing this we have the following:

Looking at the last entry in the user agent, we can see that the packet is using Firefox 25. Entering that as the flag, we’ve acquired 50 points!