Ruby/Gnome2 0.16.0 Format String Vulnerability

2007-11-29T00:00:00
ID SECURITYVULNS:DOC:18529
Type securityvulns
Reporter Securityvulns
Modified 2007-11-29T00:00:00

Description

RubyGnome2 0.16.0 Format String Vulnerability In Gtk::MessageDialog http://em386.blogspot.com

Ruby Gnome2 is a project to provide GTK2 bindings to ruby scripts so you can write GUI code in less time. There is a format string vulnerability in Gtk::MessageDialog(). This design flaw does not allow for a user generated string to be safely sent to this function.

It is really just an API to the GTK2 function gtk_message_dialog_new() Ruby/Gnome2 does not properly use a format specifier for the message variable in ruby-gnome2-all-0.16.0/gtk/src/rbgtkmessagedialog.c as requested by the Gtk man page for this function.

... w = gtk_message_dialog_new(NIL_P(parent) ? NULL : GTK_WINDOW(RVAL2GOBJ(parent)), RVAL2GFLAGS(flags, GTK_TYPE_DIALOG_FLAGS), RVAL2GENUM(type, GTK_TYPE_MESSAGE_TYPE), RVAL2GENUM(buttons, GTK_TYPE_BUTTONS_TYPE), (const gchar*)(NIL_P(message) ? "": RVAL2CSTR(message))); ...

The GTK2 documentation: http://www.gtk.org/api/2.6/gtk/GtkMessageDialog.html#gtk-message-dialog-new states that message should be a 'printf style format string' and after that should be arguments to message. However calling messagedialog from your ruby script does not support this.

The vulnerability can be exploited by sending a specially crafted string to the function. An example ruby program is provided as a POC.

...

!/usr/bin/env ruby

ruby rubber.rb %x.%x.%x.%x.%x.%x.%x.%x.%x.%x.%x.%x.%x

require 'libglade2'

my_string = ARGV[0]

dialog = Gtk::MessageDialog.new(@main_app_window, Gtk::Dialog::MODAL, Gtk::MessageDialog::INFO, Gtk::MessageDialog::BUTTONS_CLOSE, "%s - Was your string!" % my_string) dialog.run dialog.destroy ...

A temporary work around for this vulnerability is using the markup member:

dialog.markup = "#{my_string} - Was your string!"

Or

my_string = "my_string = my_string.gsub(/%/, "%%")

I have found a few ruby/gnome2 apps out there who use the API in this unsafe manner.

Fixed Nov 27th 2007 in Ruby/Gnome2 SVN