Class: Scryer::Rules::CommandInjectionRule

Inherits:
Scryer::Rule show all
Defined in:
lib/scryer/rules/command_injection_rule.rb

Overview

Flags shell-executing calls (system, ` ` backticks, %x{}, Kernel#exec, IO.popen, Open3.*) whose command string contains interpolation — user-controlled input reaching a shell is a command injection risk.

Constant Summary collapse

SHELL_METHODS = 
%w[system exec popen spawn].freeze

Instance Attribute Summary

Attributes inherited from Scryer::Rule

#file, #sexp, #source

Instance Method Summary collapse

Methods inherited from Scryer::Rule

inherited, #initialize

Constructor Details

This class inherits a constructor from Scryer::Rule

Instance Method Details

#scan ⇒ Object 



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# File 'lib/scryer/rules/command_injection_rule.rb', line 15

def scan
  findings = []

  Ast.each_node(sexp) do |node|
    # backticks / %x{} literals: [:xstring_literal, [:xstring, [:@tstring_content, ...] or [:string_embexpr, ...]]]
    if Ast.tagged?(node, :xstring_literal) && Ast.string_literal_has_interpolation?(node)
      line = Ast.line_of(node)
      findings << finding(
        line: line,
        message: "Backtick/`%x{}` shell execution contains interpolated input.",
        suggested_fix: "Avoid shelling out with interpolated strings. If you must run a " \
                        "command, use `system(\"cmd\", arg1, arg2)` (array form) so each " \
                        "argument is passed directly to the OS without going through a shell."
      )
    end

    next unless Ast.tagged?(node, :method_add_arg, :command, :command_call)

    inner = Ast.tagged?(node, :method_add_arg) ? node[1] : node
    receiver_and_name = Ast.call_name(inner)
    next unless receiver_and_name

    _receiver, method_name = receiver_and_name
    next unless SHELL_METHODS.include?(method_name)

    args = Ast.call_arguments(node)
    next if args.empty?

    first_arg = args.first
    next unless Ast.string_literal_has_interpolation?(first_arg)

    line = Ast.line_of(first_arg) || Ast.line_of(node)
    findings << finding(
      line: line,
      message: "`#{method_name}` is called with a single interpolated string, which goes " \
                "through a shell — user-controlled input here can inject arbitrary commands.",
      suggested_fix: "Pass arguments as separate strings instead of one interpolated " \
                      "string, e.g. `#{method_name}(\"cmd\", user_input)` rather than " \
                      "`#{method_name}(\"cmd \#{user_input}\")` — the array form bypasses the shell entirely."
    )
  end

  findings
end