IP Address: 172.25.200.200

Port: 9002

Want to run this Docker container locally?

docker run -d -p 9002:80 --restart always --name ctf-base64 joshbeck2024/ctf-base64-rev-shell-flag-k

<http://172.25.200.200:9002>

This time, we have a webpage with a form that expects encoded content. (If you play with the form field, you can see that it decodes from Base64 correctly.

Let’s just test it out. A great site that you’ll use all the time for encoding/decoding and encryption/decryption is CyberCheck

Google: CyberChef

Can see here that Hello World will Base64 encode to: SGVsbG8gV29ybGQ=

Let’s paste that into the Flag K submission field and submit.

In this case, we’ll want to Base64 encode our reverse shell payload. Note: The technique here is one that you’ll utilize —very— often.

First, open up a file called rev.shell using pico

pico rev.shell

This is the reverse shell code from Flag B and Flag N write ups. Save this file and close it.