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Cracking the CTF Challenge: Analyzing see-through.pcapng to Find the Flag

Oliver Ripka Oliver Ripka

Introduction to CTF and pcap Analysis

Capture-the-flag (CTF) challenges are popular in the cybersecurity world, as they test participants' skills in various security-related tasks. One common challenge involves analyzing pcap (packet capture) files to find hidden flags. In this article, we'll analyze see-through.pcapng, a CTF challenge pcap file, and show you how to find the flag using PacketSafari and Wireshark.

Finding the Flag with PacketSafari

To start, let's open see-through.pcapng on PacketSafari and begin our analysis. To find the flag, we'll filter for all initial SYN packets using the following display filter:

tcp.flags.syn == 1 and tcp.flags.ack == 0

After applying the filter, right-click on the fourth packet (packet 35) in the list and select "Follow->TCP".

Scroll down through the contents of the TCP stream, and you'll find the flag hidden among the data.

Alternative way

Instead of following the TCP stream this time, you can also look for the flag in the packet list directly. Go to the lower-right corner of Wireshark and select packet 83. Examine the hex view, and you'll see the flag in plain sight.

Additional Tips and Tricks

When analyzing pcap files for CTF challenges, it's important to be familiar with various Wireshark filters and techniques, as these can significantly speed up the process. In our example, knowing how to filter for initial SYN packets helped us find the flag quickly. Additionally, being comfortable with both PacketSafari and Wireshark can provide extra flexibility and options when tackling challenges.

Conclusion and Further Learning

In this article, we've demonstrated how to find a hidden flag in the see-through.pcapng CTF challenge using both PacketSafari and Wireshark. By applying the right filters and examining packet contents, we were able to locate the flag quickly and efficiently.

To further improve your packet analysis skills, consider enrolling in the WIRED for Packet Analysis course. This comprehensive training program will teach you expert techniques and real-world examples to help you become a master in pcap analysis.