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Final Event Style Sample Challenge - KPRCA_00056

Original Versions

Known Vulnerabilities

  • CWE-787 - Out-of-bounds Write
  • CWE-823 - Use of Out-of-range Pointer Offset

DARPA performer group

Kaprica Security (KPRCA)


Headscratch is an esoteric programming. Writing in headscratch is very tedious, results in obscenely verbose programs, and will leave most programmers scrating their heads out of confusion and frustration. This challenge binary implements a headscratch interpreter.

Feature List

Headscratch supports the following statements.

  • > Increment the data pointer.
  • _ Decrement the data pointer.
  • + Increment the value at the data pointer.
  • - Decrement the value at the data pointer.
  • [ Go to matching ] if the value at the data pointer is zero.
  • ] Go to matching [ if the value at the data pointer is not zero.
  • . Output the value at the data pointer.
  • , Read a value in and store it at the data pointer.


Within the interpreter exists a data pointer that points into memory which can be modified by the currently running program. One of the statements available to programmers of headscratch is the '>' statement which increments the data pointer to point to the next byte in the section of memory used to store the data available to a program. When incrementing the data pointer, the interpreter does not check to make sure that the data pointer does not go past the upper bounds of the data array which is stored on the stack. Therefore, it is possible to increment that data pointer past the bounds of the array and onto the stack frame where the program can then arbitrarily modify the stack frame. This results in a type 1 vulnerability.

Generic class of vulnerability

Unchecked pointer use.

CWE classification

CWE-787: Out-of-bounds Write CWE-823: Use of Out-of-range Pointer Offset


The primary challenge with exploiting this challenge binary is that a CRS must be able to construct a Headscratch program that allows for the exploitation the vulnerability.

Subjective Quantification

Discovering: Easy Proving: Medium Fixing: Easy

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