Class: Brakeman::CheckExecute

Inherits:
BaseCheck show all
Defined in:
lib/brakeman/checks/check_execute.rb

Overview

Checks for string interpolation and parameters in calls to Kernel#system, Kernel#exec, Kernel#syscall, and inside backticks.

Examples of command injection vulnerabilities:

system(“rf -rf #:file”) exec(params) `unlink #params[:something`

Constant Summary collapse

SAFE_VALUES =
[s(:const, :RAILS_ROOT),
s(:call, s(:const, :Rails), :root),
s(:call, s(:const, :Rails), :env)]

Constants inherited from BaseCheck

BaseCheck::CONFIDENCE

Constants included from Util

Util::ALL_PARAMETERS, Util::COOKIES, Util::COOKIES_SEXP, Util::PARAMETERS, Util::PARAMS_SEXP, Util::PATH_PARAMETERS, Util::QUERY_PARAMETERS, Util::REQUEST_ENV, Util::REQUEST_PARAMETERS, Util::REQUEST_PARAMS, Util::SESSION, Util::SESSION_SEXP

Constants inherited from SexpProcessor

SexpProcessor::VERSION

Instance Attribute Summary

Attributes inherited from BaseCheck

#tracker, #warnings

Attributes inherited from SexpProcessor

#context, #env, #expected

Instance Method Summary collapse

Methods inherited from BaseCheck

#add_result, inherited, #initialize, #process_call, #process_cookies, #process_default, #process_if, #process_params, #process_string_interp

Methods included from Util

#array?, #block?, #call?, #camelize, #contains_class?, #context_for, #cookies?, #false?, #file_by_name, #file_for, #github_url, #hash?, #hash_access, #hash_insert, #hash_iterate, #integer?, #make_call, #node_type?, #number?, #params?, #pluralize, #regexp?, #relative_path, #request_env?, #request_value?, #result?, #set_env_defaults, #sexp?, #string?, #symbol?, #table_to_csv, #template_path_to_name, #true?, #truncate_table, #underscore

Methods included from ProcessorHelper

#class_name, #process_all, #process_all!, #process_call_args, #process_class, #process_module

Methods inherited from SexpProcessor

#error_handler, #in_context, #initialize, #process, #process_dummy, #scope

Constructor Details

This class inherits a constructor from Brakeman::BaseCheck

Instance Method Details

#check_for_backticks(tracker) ⇒ Object

Looks for calls using backticks such as

`rm -rf #:file`


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# File 'lib/brakeman/checks/check_execute.rb', line 72

def check_for_backticks tracker
  tracker.find_call(:target => nil, :method => :`).each do |result|
    process_backticks result
  end
end

#dangerous?(exp) ⇒ Boolean

Returns:

  • (Boolean)

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# File 'lib/brakeman/checks/check_execute.rb', line 105

def dangerous? exp
  exp.each_sexp do |e|
    next if node_type? e, :lit, :str
    next if SAFE_VALUES.include? e

    if call? e and e.method == :to_s
      e = e.target
    end

    if node_type? e, :or, :evstr, :string_eval, :string_interp
      if res = dangerous?(e)
        return res
      end
    else
      return e
    end
  end

  false
end

#dangerous_interp?(exp) ⇒ Boolean

Returns:

  • (Boolean)

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# File 'lib/brakeman/checks/check_execute.rb', line 126

def dangerous_interp? exp
  match = include_interp? exp
  return unless match
  interp = match.match

  interp.each_sexp do |e|
    if res = dangerous?(e)
      return Match.new(:interp, res)
    end
  end

  false
end

#process_backticks(result) ⇒ Object

Processes backticks.


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# File 'lib/brakeman/checks/check_execute.rb', line 79

def process_backticks result
  return if duplicate? result

  add_result result

  exp = result[:call]

  if input = include_user_input?(exp)
    confidence = CONFIDENCE[:high]
    user_input = input.match
  elsif input = dangerous?(exp)
    confidence = CONFIDENCE[:med]
    user_input = input
  else
    return
  end

  warn :result => result,
    :warning_type => "Command Injection",
    :warning_code => :command_injection,
    :message => "Possible command injection",
    :code => exp,
    :user_input => user_input,
    :confidence => confidence
end

#process_result(result) ⇒ Object

Processes results from Tracker#find_call.


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# File 'lib/brakeman/checks/check_execute.rb', line 38

def process_result result
  call = result[:call]
  args = call.arglist
  first_arg = call.first_arg

  case call.method
  when :system, :exec
    failure = include_user_input?(first_arg) || dangerous_interp?(first_arg)
  else
    failure = include_user_input?(args) || dangerous_interp?(args)
  end

  if failure and not duplicate? result
    add_result result

    if failure.type == :interp #Not from user input
      confidence = CONFIDENCE[:med]
    else
      confidence = CONFIDENCE[:high]
    end

    warn :result => result,
      :warning_type => "Command Injection", 
      :warning_code => :command_injection,
      :message => "Possible command injection",
      :code => call,
      :user_input => failure.match,
      :confidence => confidence
  end
end

#run_checkObject

Check models, controllers, and views for command injection.


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# File 'lib/brakeman/checks/check_execute.rb', line 21

def run_check
  Brakeman.debug "Finding system calls using ``"
  check_for_backticks tracker

  Brakeman.debug "Finding other system calls"
  calls = tracker.find_call :targets => [:IO, :Open3, :Kernel, :'POSIX::Spawn', :Process, nil],
    :methods => [:capture2, :capture2e, :capture3, :exec, :pipeline, :pipeline_r,
      :pipeline_rw, :pipeline_start, :pipeline_w, :popen, :popen2, :popen2e, 
      :popen3, :spawn, :syscall, :system]

  Brakeman.debug "Processing system calls"
  calls.each do |result|
    process_result result
  end
end