Server-side code injection (Ruby)

Description

The target application was found vulnerable to code injection. A malicious actor could inject arbitrary Ruby code to be executed on the server. This could lead to a full system compromise by accessing stored secrets, injecting code to take over accounts, or executing OS commands.

Remediation

Never pass user input directly into functions which evaluate string data as code, such as eval, send, public_send, instance_eval or class_eval. There is almost no benefit of passing string values to these methods, as such the best recommendation is to replace the current logic with more safe implementations of dynamically evaluating logic with user input. If using send or public_send ensure the first argument is to a known, hardcoded method/symbol and does not come from user input.

For eval, instance_eval and class_eval, user input should never be sent directly to these methods. One alternative is to store functions or methods in a Hash that can be looked up using a key. If the key exists, the function can be executed.

def func_to_run
  puts 'hello world'
end

input = 'fn'

function_map = { fn: method(:func_to_run) }

if function_map.key?(input.to_sym)
  function_map[input.to_sym].call
else
  puts 'invalid input'
end

Details

Links

• CWE