From: Dave Burt <dave@...>
Date: 2005-01-27T23:05:54+09:00
Subject: Re: When little languages grow...

"ts" <decoux@moulon.inra.fr> wrote:
> Well, a better example is
>
> uln% cat b.rb
> #!/usr/local/bin/ruby
> source = <<EOT
> a = Object.new
> class << a
>   def to_s
>      puts "hello :-)"
>      super
>   end
> end
> a
> EOT
>
> puts Thread.new { $SAFE = 4; eval source }.value
> uln%
>
> uln% b.rb
> hello :-)
> #<Object:0x2a955c0738>
> uln%
>
>
> i.e. you *MUST* validate the object with $SAFE = 4 and never trust it.

Like this?

    Thread.new { $SAFE = 4; puts eval(source) }

Or like this?

    puts Thread.new { $SAFE = 4; String.new(eval(source).to_s) }.value

Both of these generate the SecurityError that your example above bypasses by 
running at $SAFE=0.

Dave