I got the [a.out](https://github.com/mar232320/ctf-writeups/raw/main/umassctf2021/a.out) file which runs a web server. I also have a website link [http://34.72.232.191:8080/](http://34.72.232.191:8080/)
This was very easy challenge for me overall. When I went to the webserver page I found this content
# Dynamic pages!!! /page?args ? (this is also a 404 page...)
Try going to /echo?message
I echoed some data - for example /echo?test and the web page displayed `test` Echo is a linux command so as it was written in the main page I tried cat/cat?flag.txt
The site returned `UMASS{f^gJkmvYq` so I added }  to the flag> UMASS{f^gJkmvYq}