PicoCTF-2021 Writeup
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  1. Forensics

Wireshark twoo twooo two twoo...

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Last updated 2 years ago

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Problem

Can you find the flag? shark2.pcapng.

Solution

  1. Upon initial inspection, there seem to be a lot of requests to a /flag endpoint. Each request shows a different flag so these must be a distraction.

  2. After searching through the file I noticed many DNS requests for various subdomains of reddshrimpandherring.com. This looks like the suspicious traffic that one of the challenge hints refers to.

  3. A lot of the DNS queries have a destination of 8.8.8.8. However, a subset have a destination for 18.217.1.57.

  4. We can apply the filter dns and ip.dst==18.217.1.57 to only see DNS requests to this IP address. If we take the subdomains of reddshrimpandherring.com and append them in order we get: cGljb0NURntkbnNfM3hmMWxfZnR3X2RlYWRiZWVmfQ==

  5. Decoding the above string as base64 gives us the flag.

  6. Alternatively, this file can be analyzed using . Just upload the file, go to the DNS page, and scroll down to see the requests neatly organized.

Flag

picoCTF{dns_3xf1l_ftw_deadbeef}

shark2.pcapng
apackets.com