No one expects command execution

Re:No one expects command execution by krylon on Friday July 03, 2015 @01:11PM (#9826729)

Perl has a special "taint" mode (Ruby does, too, I think, but I don't know about the differences or similarties), where any data coming from outside the program - environment variables, network connections, files, etc. - is considered "tainted", i.e. treated as bad, until you validate it using regular expressions (or something along those lines). I have to admit I never tried it, but it sounds like a good idea, assuming it works as advertised, when dealing with potentially malicious input or paranoia.

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Re:No one expects command execution by JonnieCache on Friday July 03, 2015 @01:17PM (#9826766)

Rails has ActiveSupport::SafeBuffer for doing XSS protection, but ruby doesn't track external strings as dirty like that.

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Re:No one expects command execution by vidarh on Friday July 03, 2015 @02:14PM (#9827072)

> but ruby doesn't track external strings as dirty like that.

Yes, it does. E.g:

    x = STDIN.gets
    puts x.tainted?
    y = "hello "+x
    puts y.tainted?
    z = "foo"
    puts z.tainted?

The two first will return "true", and the last will print "false". If you set the safe-level appropriately some methods will be disallowed for x and y above (e.g. eval()), though I would not trust that as comprehensive, but it's a lot better than nothing.

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Re:No one expects command execution by flgr on Friday July 03, 2015 @02:09PM (#9827034)

> but ruby doesn't track external strings as dirty like that.

It does:

  irb(main):001:0> gets.tainted?
  foo
  => true

You can even set $SAFE to 1 or higher to disallow the use of tainted strings in potentially dangerous commands:

  freya:~ flgr$ ruby -e '$SAFE = 1; system "tar bla bla #{gets}"'
  foo
  -e:1:in `system': Insecure operation: -r (SecurityError)
	  from -e:1:in `<main>'

See http://phrogz.net/programmingruby/taint.html for more information.

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