Saas

The challenge is to bypass the checks to get the flag. The description gave the basic idea that it uses sed. This is a pretty straightforward challenge if you are familiar with bash. After reading the blacklist I used to wildcard operator to bypass the checks. You input this:

'' *

And you find the flag in the output

flag >> ictf{:roocu:roocu:roocu:roocu:roocu:roocursion:rsion:rsion:rsion:rsion:rsion:_473fc2d1}