Regina.md

Author: @JohnHammond#6971

I have a tyrannosaurus rex plushie and I named it Regina! Here, you can talk to it :)

---

Entering the challenge, we are greeted with a banner:

/usr/local/bin/regina: REXX-Regina_3.9.4(MT) 5.00 25 Oct 2021 (64 bit)

A quick google search shows this is a rather popular interpreter that I have never heard of. It has a very thorough man page located here. However, no matter what my input is, I cannot seem to get a response. I learned the proper syntax that should work for testing purposes, but nothing connects back:

/usr/local/bin/regina: REXX-Regina_3.9.4(MT) 5.00 25 Oct 2021 (64 bit)
Say "Test"

client_loop: send disconnect: Broken pipe

After trying things for quite a while, right before giving up, I miraculously stumbled upon a response somehow:

/usr/local/bin/regina: REXX-Regina_3.9.4(MT) 5.00 25 Oct 2021 (64 bit)
'say test'
;
run
'say test';
Say "Test";
exec
run
;
go
^F
mysh: say: not found
 
^Fmy
my
sh: RUN: not found

sh: say: not found
Test
 
sh: EXEC: not found

sh: RUN: not found
Ssh: GO: not found
Connection to challenge.nahamcon.com closed.

While just enough to keep me from giving up, I had a lot of trouble recreating this still. While I had pressed ^F in the cli, I was under the impression that I also had pressed ^D and this keystroke was important for the execution. However, simply pressing ^D on its own ended up terminating the ssh connection.

Eventually I landed on a goofy pattern to execute, where I write my commands, quickly press the enter key two times, immediately followed by ^D, then another enter stroke. With this, my commands would be executed and then the connection terminated.

/usr/local/bin/regina: REXX-Regina_3.9.4(MT) 5.00 25 Oct 2021 (64 bit)
ADDRESS SYSTEM "ls"
Say "Test"


  
flag.txt
Test
Connection to challenge.nahamcon.com closed.

/usr/local/bin/regina: REXX-Regina_3.9.4(MT) 5.00 25 Oct 2021 (64 bit)
ADDRESS SYSTEM "cat flag.txt"
Say "Test"



  
flag{2459b9ae7c704979948318cd2f47dfd6}
Test
Connection to challenge.nahamcon.com closed.

CTRL+D is commonly used for exiting programs, so it is somewhat sensible that it finalizes REXX-Regina for execution. Was this intended, though? It certainly felt like a strange way to interact.