An attempt at creating a Ruby sandbox in pure Ruby. (Research only; do not rely on this for security.)
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.



Do not rely on this for security. It is a research experiment, and I have minimal security experience. If you need to run untrusted code, please get the assistance of somebody who actually knows security and understands sandboxing.

And remember, blacklists are always ineffective — use whitelists instead.

An attempt at creating a Ruby sandbox in pure Ruby.

Build Status Code Coverage Code Climate Dependencies Stories in Ready


gem install sicuro



If you wish to set the memory or time limits, you will need to manually create a Sicuro instance:

s =, timelimit)

memlimit is in megabytes, and timelimit is in seconds. The defaults are 50MB RAM and 5 seconds.

There is no way to alter the strength of the sandbox.

Running code in the sandbox

Sicuro.eval(code) is an alias for, and returns a Sicuro::Evaluation instance.


Sicuro::Evaluation#code is the code passed to Sicuro#eval.

Sicuro::Evaluation#stdout is anything printed to stdout by the evaluated code (puts, print, etc).

Sicuro::Evaluation#stderr is anything printed to stderr by the evaluated code (warn).

Sicuro::Evaluation#return is the returned value of the last statement.

Sicuro::Evaluation#to_s intelligently returns one of #stdout or #stderr.

Notes on Sicuro::Evaluation#return

Previously, Sicuro provided a #return method that would give the value returned by the last line of code it evaluated. It existed from v0.0.1 to v0.18.0 (inclusive), and was removed with v0.19.0. The way this was accomplished was by returning a JSON object from the child (sandboxed) process to the parent (non-sandboxed) process. However, this approach led to bugs with errors about encoding things to JSON being intermixed with the other results, which gave rather bizarre errors when reaching the parent process.

I plan to eventually either reintroduce this exact functionality in a more robust form, or replace it with a better alternative later on.


Example 1:

require 'sicuro'

s = Sicuro.eval('puts "hi!"')
s.code      # returns "puts \"hi!\""
s.stdout    # returns "hi!\n"
s.stderr    # returns ""
s.to_s      # returns "hi!\n", because it uses #stdout

Example 2:

require 'sicuro'

s = Sicuro.eval('"hi!"')
s.code      # returns "\"hi!\""
s.stdout    # returns ""
s.stderr    # returns ""
s.to_s      # returns "\"hi!\"", because it uses #return compatibility

Sicuro is now API-compatible with the gem.

require 'sicuro'

p, "puts 'lawl'")

# Example output:
#   #<Sicuro::Evaluation code="puts 'lawl'" stdout="lawl\n" stderr="" wall_time=36>


Sicuro is released under the ISC license. See the LICENSE file which should have been distributed with this for more information.