Qualifier Challenge - KPRCA_00011

Original Versions

Known Vulnerabilities

  • CWE-121 - Stack-based Buffer Overflow
  • CWE-416 - Use After Free
  • CWEs are listed as indicated by the challenge author.


  • DeepRed: 2.0
  • CSDS: 0.54
  • CodeJitsu: 0.0
  • Disekt: 0.0
  • ForAllSecure: 0.0
  • Lekkertech: 0.0
  • TECHx: 0.0
  • Shellphish: 0.0
  • FuzzBOMB: 0.0
  • TrailofBits: 0.0
  • The maximum score for each challenge in CQE is 4, following the CQE Scoring Document.

Passed consensus evaluation

  • CodeJitsu - CB1
  • CSDS - CB1
  • DeepRed - CB1
  • TrailofBits - CB1

Proved a POV in reference challenge

Defense against reference POVs

  • TrailofBits: 100.0% - CB1
  • CodeJitsu: 100.0% - CB1
  • Disekt: 100.0% - CB1
  • CSDS: 100.0% - CB1
  • DeepRed: 100.0% - CB1

No submission

  • Eighth Place Team
  • Eleventh Place Team
  • Fifth Place Team - Finalist
  • First Place Team - Finalist
  • Fourth Place Team - Finalist
  • Ninth Place Team
  • Second Place Team - Finalist
  • Seventh Place Team - Finalist
  • Sixth Place Team - Finalist
  • Tenth Place Team
  • Third Place Team - Finalist
  • Thirteenth Place Team
  • Twelfth Place Team

All Submissions

Author Information

"Brian Pak" brian.pak@kapricasecurity.com

DARPA performer group

Kaprica Security (KPRCA)


This is a simple movie rental service where the user can list available movies in the inventory and rent the ones that are not rented already. The user is also able to return the movie. There is also an interface for privileged user (admin) when successfully logged in. This interface allows the admin to add, remove, or update movies in the inventory.

Feature List

This service supports the following features:

In normal mode,

  1. List movies: lists a full movie list as well as a rental list (i.e. the movies that are currently rented).
  2. Rent movie: allows the user to rent a movie from the list (movies that are not currently rented can be rented).
  3. Return movie: allows the user to return the movie that was rented.
  4. Admin mode (login): verifies username and password to provide privileged menus.
  5. Exit: quits the program.

In admin mode,

  1. Add movie: adds a new movie to the list.
  2. Remove movie: removes a movie from the list.
  3. Update movie: updates information about a movie.
  4. Quit admin mode: quits the admin mode and goes back to the normal mode.


Upon specific sequence of actions (and appropriate input), it is possible to cause a use-after-free (UAF) bug and crash the program. With specially crafted input, arbitrary code execution is also possible.

There are actually 2 bugs in the service. The first bug allows the attacker to get into admin mode without knowing the correct password. There exists a stack buffer overflow which results in the overwrite of the return status local variable that determines if the login was successful. However, this bug is not enough to crash the service. The second bug is a UAF bug with the movie lists, where the rental list holds a stale pointer to the free'd movie entry.

Specifically, in main.c:445, when the movie is removed (in admin menu), it is removed only from the full list, not the rented list. Then, by allocating memory of size equivalent of the movie object, it is possible to control the contents of the stale movie pointer, which has a function pointer in it. By setting the function pointer, EIP control is possible.

Generic class of vulnerability

Stack Buffer Overflow


CWE classification

Stack-based Buffer Overflow (CWE-121)

Use-After-Free (CWE-416)


This CB tests if the competitors can chain two vulnerabilities to perform a successful attack. Since the password for the admin account is randomly generated each time the program is run, the stack buffer overflow needs to be used to bypass the login validation. It requires a good understanding of how the memory allocation and free work. Also, in order to successfully crash the program, one needs to use both modes (normal & admin) in a specific order to manipulate the layout of the heap.

Curated by Lunge Technology, LLC. Questions or comments? Send us email