Assignment 2 75 pts + 25pts extra for sploit4

Deadline: Thursday, April 23, 2020 by 12:30:00 PM Pacific Time

The goal of this assignment is to gain hands-on experience with the effects of buffer overflows and other memory-safety bugs. You are allowed to work in teams for this assignment.

sploit1-sploit3 are required. sploit4 is extra credit!

Getting Started

To complete this assignment you will be provided with a VirtualBox VM and a set of files.

VM Image

In order to match the environment in which your submission will be graded, all work for this assignment must be done on the VirtualBox VM we have provided, named pa2box. You can download the VM image here.

Import the pa2box.vbox file into VirtualBox via the MachineAdd menu item. Don't create a brand-new VirtualBox VM or import the pa2box-data.vmdk file on its own: if you do this, you won't have the correct configuration.

After importing the VM, select it in the VirtualBox sidebar and start it with the green arrow button or the MachineStart menu item. The VM is configured with two users: student, with password hacktheplanet; and root, with password hackallthethings. Instead of using the command line through VirtualBox, we recommend that you SSH into your VM from another client. The VM image is configured to expose an SSH server on port 2222 of your system's loopback address (

To SSH into the VM (from your host system running VirtualBox, not from inside the VM):

ssh -p 2222 student@

To copy files from your computer to the VM:

scp -P 2222 -r /path/to/files/ student@

To copy files from the VM to your computer:

scp -P 2222 student@ /destination/path

Please note that SSH is disabled for root, so you can only SSH in as the student user. You can still log in as root using su or by logging into the VM directly.

Assignment Files

Starter files are included inside the student home directory of the VM image.

The targets directory contains a Makefile to generate target executables specific to your PID (as well as a folder called base, which you should not modify, used to generate the targets).

Exploit starter code can be found in the sploits1-sploits4 directories: one per each of the four vulnerable target programs. Each of these contains a Makefile, a shellcode.h header file providing Aleph One's shellcode, and a sploitN.c file in which you should write your exploit code (in addition to an assignment.toml file, which should not be modified).

You will be writing an exploit for each of the four vulnerable programs provided in the assignment. Each exploit, when run in the VM with its target installed setuid-root in /tmp, should yield a root shell (/bin/sh). You can verify that the shell has been launched as root by typing whoami, to which you should see the response root. You must use Aleph One's shellcode in shellcode.h, as this will be used in the grading scripts.

For each exploit, in addition to your .c file, please also create a corresponding file writeup.txt containing a brief description of how the exploit works.

Exploit Generation

To complete the assignment, you will need to: generate targets specific to your PID; use GDB to find vulnerabilities in the targets; and, finally, craft your exploit programs.

Generating the Targets

Run make generate in the targets directory to create the four target source files specific to you. This will prompt you for your student ID (A######## or U########), which will be used to randomize portions of the contents of target1.c-target4.c.

Run make to build the target binaries target1-target4.

Run sudo make install to copy the binaries into the /tmp directory.

Finally, run sudo make setuid to mark the binaries as setuid-root. If you forget this step, then your exploits will end up launching a normal shell instead of a root shell!

Exploit Notes

For this assignment you should read and have a solid understanding of Aleph One's “Smashing the Stack for Fun and Profit”.

Aleph One gives code that calculates addresses on the target’s stack based on addresses on the exploit’s stack. However, addresses on the exploit’s stack can change based on how the exploit is executed (working directory, arguments, environment, etc.). You must therefore hard-code target stack locations in your exploits.

You should not use a function such as get_sp() in the exploits you hand in. You should only modify the sploitN.c files and corresponding writeup.txt files; i.e., your exploits should work with unmodified Makefiles, targets, etc. In grading, the exploits may be run with a different working directory. Your exploits must work in these cases also. If you hard-code the target's stack locations into your exploit you should be fine. Your exploit programs should not take any command-line arguments.

Shutting down the VM removes the files in /tmp; if you want to keep them, pause the VM and save its state!

IMPORTANT: Using the shellcode

The shellcode is defined for you in shellcode.h inside each sploitN/ directory. To use the shellcode in your sploit buffers, please import the shellcode with #include and copy the contents programatically. You can do this with memcpy, strcpy, or even just a for loop with array assignments. Please do NOT manually copy-paste the shellcode string literal into your sploitN.c file. While the sploit will still work, it may break grading.

Using GDB

To run an exploit in GDB, run, e.g., gdb sploit1 to execute sploit1.

Note that there are two executables when we run these programs, since, e.g., sploit1 will execute target1. Because of this, you can use the following sample workflow to get started in GDB:

  1. b main --- break at main in sploit1.c
  2. r --- run the executable sploit1
  3. c --- continue until main in target1.c
  4. b foo --- set a breakpoint at foo in target1.c

Note that if you try to set breakpoints in targetN before the program has started executing targetN, e.g., if you tried to run b foo before step 3, you may get the following message:

Make breakpoint pending on future shared library load? (y or [n])

Type y will also set the breakpoints in targetN.

Here are some additional GDB commands that may come in handy:

Also refer back to the sample commands in Assignment 1.

Note that this is only a cursory overview of GDB; much more info is available from online resources.


  1. Create a file named PID in the student home directory on the VM, and put your PID in it (ex: A12345678)
  2. Run the following command from the student home directory tar -czvf pa2.tar.gz PID sploit[1-4]/ targets/ This will create a pa2.tar.gz in the home directory with all your files in it. You can see what files were zipped by running tar -tf pa2.tar.gz
  3. scp the pa2.tar.gz file to your local computer and submit to gradescope.
  4. If you work in teams, only one of you need to submit your code to gradescope. After submission, you can find the Add Group Member button to add your teammate.

Note: The autograder will only check whether your sploits can be compiled successfully. The score is only a reference for you to see if you pass all compilation test easily. In the meanwhile, you'll know your answer is correct if you followed the instructions above and you were able to get a root shell. The actual score for this assignment will be posted when we are done with grading and you will be notified.