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

grace-hopper-1

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.

cyberheroines.sh cyberheroines.txt vulnerable.php

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.

Command: rev cyberheroines.txt

Output: -  7a34781dbf938ac21363742c7e3e18344c663990279d20daa8b2cc009bc94d2e

Not good, the flag seems to be hashed. What's the sh file anyway?

Command: rev cyberheroines.sh

Output:
"}Y@w_3#T_s!_$!#t{FTCHC"=GALF
txt.seniorehrebyc > mus652ahs | "GALF$" n- ohce

Reverse the text:

echo -n "$FLAG" | sha256sum > cyberheroines.txt
FLAG="CHCTF{t#!$_!s_T#3_w@Y}"

Flag: CHCTF{t#!$_!s_T#3_w@Y}