Grace Hopper
Grace Brewster Hopper
Grace Brewster Hopper (née Murray; December 9, 1906 – January 1, 1992) was an American computer scientist, mathematician, and United States Navy rear admiral. One of the first programmers of the Harvard Mark I computer, she was a pioneer of computer programming who invented one of the first linkers. Hopper was the first to devise the theory of machine-independent programming languages, and the FLOW-MATIC programming language she created using this theory was later extended to create COBOL, an early high-level programming language still in use today. - Wikipedia Entry
Description
Chal: Command this webapp like this Navy Real Admiral
Alternate (Better) Connection: webapp
Author: Sandesh
Solution
The application allows us to run console commands. The first command I tried was ls, but got following output: You think it's that easy? Try harder!. Some commands are being filtered, because id works: uid=33(www-data) gid=33(www-data) groups=33(www-data)
Getting around ls is quite easy, echo * will do the trick.
The echo * command in Linux prints all the files and directories in the current directory to the standard output. The asterisk (*) is a wildcard character that matches any character. So, the echo * command will print all the files and directories, regardless of their names.
We found the files, now to read them. Here we are also limited on commands. I tried cat, tac, more, less, head, tail, but none of them worked. Linux has rev program which reverses the text and using rev we can read file.
Not good, the flag seems to be hashed. What's the sh file anyway?
Reverse the text:
Flag: CHCTF{t#!$_!s_T#3_w@Y}
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