ctf-writeups

Ruby Master - Level 3 150 points

题意

Final level, beat it!

Steal flag from level3.rb and level3_flag.rb

The attachment is the same is level 1 & 2

Server: nc host port

Attachment: ruby_master.zip

解题步骤

任务：

level3.rb:

require_relative 'restrict'
Restrict.set_timeout

def get_flag(x)
  flag = "THUCTF{CENSORED}"
  x
end

input = STDIN.gets
fail unless input
input.size > 60 && input = input[0, 60]

Restrict.seccomp

STDOUT.puts get_flag(eval(input))

level3_flag.rb:

# FLAG is THUCTF{CENSORED}

虽然文字在注释中，但仍然在内存里。

ObjectSpace.each_object(String) {|x| p x if /THUCTF\{/ =~ x}

得到：

# FLAG is THUCTF{Th3_rea1_RUBY_Mast3r_1s_y0u!}