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Title:</span></b><span style='font-family:"Arial","sans-serif"'> How to Exploit Thread Safety Problems <o:p></o:p></span></p> <p class=MsoNormal><b><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></b></p> <p class=MsoNormal><b><span style='font-family:"Arial","sans-serif"'>Concept / Topic To Teach:</span></b><span style='font-family:"Arial","sans-serif"'> <o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>Web applications can handle many HTTP requests simultaneously. Developers often use variables that are not thread safe. Thread safety means that the fields of an object or class always maintain a valid state when used concurrently by multiple threads. It is often possible to exploit a concurrency bug by loading the same page as another user at the exact same time. <br> Because all threads share the same method area, and the method area is where all class variables are stored, multiple threads can attempt to use the same class variables concurrently. <o:p></o:p></span></p> <p class=MsoNormal><b><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></b></p> <p class=MsoNormal><b><span style='font-family:"Arial","sans-serif"'>General Goal(s):</span></b><span style='font-family:"Arial","sans-serif"'> <o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>The user should be able to exploit the concurrency error in the web application and view login information for another user that is attempting the same function at the same time. <o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><b><span style='font-family:"Arial","sans-serif"'>This will require the use of two browser windows</span></b><span style='font-family:"Arial","sans-serif"'>.<o:p></o:p></span></p> <p class=MsoNormal><span style='font-size:8.0pt;font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal style='page-break-after:avoid'><span style='font-size:8.0pt; font-family:"Arial","sans-serif";mso-no-proof:yes'><!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"/> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"/> <v:f eqn="sum @0 1 0"/> <v:f eqn="sum 0 0 @1"/> <v:f eqn="prod @2 1 2"/> <v:f eqn="prod @3 21600 pixelWidth"/> <v:f eqn="prod @3 21600 pixelHeight"/> <v:f eqn="sum @0 0 1"/> <v:f eqn="prod @6 1 2"/> <v:f eqn="prod @7 21600 pixelWidth"/> <v:f eqn="sum @8 21600 0"/> <v:f eqn="prod @7 21600 pixelHeight"/> <v:f eqn="sum @10 21600 0"/> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"/> <o:lock v:ext="edit" aspectratio="t"/> </v:shapetype><v:shape id="Picture_x0020_15" o:spid="_x0000_i1027" type="#_x0000_t75" style='width:480pt;height:276.75pt;visibility:visible;mso-wrap-style:square'> <v:imagedata src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image001.png" o:title=""/> </v:shape><![endif]--><![if !vml]><img width=640 height=369 src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image002.jpg" v:shapes="Picture_x0020_15"><![endif]></span></p> <p class=MsoCaption>Figure <!--[if supportFields]><span style='mso-element: field-begin'></span><span style='mso-spacerun:yes'>�</span>SEQ Figure \* ARABIC <span style='mso-element:field-separator'></span><![endif]--><span style='mso-no-proof:yes'>1</span><!--[if supportFields]><span style='mso-element: field-end'></span><![endif]--> Lesson 2<span style='font-size:8.0pt;font-family: "Arial","sans-serif"'><o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><b style='mso-bidi-font-weight:normal'><span style='font-family:"Arial","sans-serif"'>Solution:<o:p></o:p></span></b></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>Open a new browser window by pressing CTRL-N. Position the window so that you see both input fields. Enter user name "dave" in the left window and user name "jeff" in the right window.<o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>Click very fast on the submit button in the right window and then in the left window.<o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal style='page-break-after:avoid'><span style='font-family: "Arial","sans-serif";mso-no-proof:yes'><!--[if gte vml 1]><v:shape id="Picture_x0020_16" o:spid="_x0000_i1026" type="#_x0000_t75" style='width:480pt;height:262.5pt; visibility:visible;mso-wrap-style:square'> <v:imagedata src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image003.png" o:title="" cropbottom="5791f"/> </v:shape><![endif]--><![if !vml]><img width=640 height=350 src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image004.jpg" v:shapes="Picture_x0020_16"><![endif]></span><span style='font-family:"Arial","sans-serif"'><o:p></o:p></span></p> <p class=MsoCaption><span style='font-family:"Arial","sans-serif"'>Figure </span><!--[if supportFields]><span style='font-family:"Arial","sans-serif"'><span style='mso-element:field-begin'></span><span style='mso-spacerun:yes'>�</span>SEQ Figure \* ARABIC <span style='mso-element: field-separator'></span></span><![endif]--><span style='font-family:"Arial","sans-serif"'><span style='mso-no-proof:yes'>2</span></span><!--[if supportFields]><span style='font-family:"Arial","sans-serif"'><span style='mso-element:field-end'></span></span><![endif]--><span style='font-family:"Arial","sans-serif"'> 2 Browser Windows<o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>The result should be that you receive the same data in both windows, even when using a different user name!<o:p></o:p></span></p> <p class=MsoNormal style='page-break-after:avoid'><span style='font-family: "Arial","sans-serif";mso-no-proof:yes'><!--[if gte vml 1]><v:shape id="Picture_x0020_35" o:spid="_x0000_i1025" type="#_x0000_t75" style='width:480pt;height:274.5pt; visibility:visible;mso-wrap-style:square'> <v:imagedata src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image007.png" o:title="" cropbottom="3061f"/> </v:shape><![endif]--><![if !vml]><img width=640 height=366 src="/WebGoat/lesson_solutions/ThreadSafetyProblem_files/image009.jpg" v:shapes="Picture_x0020_35"><![endif]></span></p> <p class=MsoCaption>Figure <!--[if supportFields]><span style='mso-element: field-begin'></span><span style='mso-spacerun:yes'>�</span>SEQ Figure \* ARABIC <span style='mso-element:field-separator'></span><![endif]--><span style='mso-no-proof:yes'>3</span><!--[if supportFields]><span style='mso-element: field-end'></span><![endif]--> Lesson 2 Completed<span style='font-family:"Arial","sans-serif"'><o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>The root-cause of this exploit is that the Java code uses a static variable for the user name. When submitting twice, the same thread and hence the same static variable containing the username of the first request will be used. <o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>This is obvious when examining the Java code:<o:p></o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p> <p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>private static String currentUser;<o:p></o:p></span></p> <p class=MsoNormal><o:p> </o:p></p> </div> <table align='RIGHT' cellspacing='0' width='90%' border='0' cellpadding='0'> <tr> <td valign='MIDDLE' width='100%' align='RIGHT class=MsoNormal' style='font-family:"Arial","sans-serif"'> Solution by Erwin Geirnaert </td> <td valign='MIDDLE' align='RIGHT'><img hspace='0' vspace='0' border='0' alt='ZION SECURITY' src='images/logos/zionsecurity.gif'></td> </tr> </table> </body> </html>