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Heap Overflows

Updated: Jan 12, 2023

Introduction


Heap overflow vulnerabilities are a type of memory corruption vulnerability that occurs when a program allocates memory from the heap and then writes more data than it can hold. This can lead to a buffer overflow, which can be exploited by attackers to gain access to a system or execute malicious code. Heap overflows can be difficult to detect and exploit, but they can have serious consequences for an organization's security. In this article, we'll take a look at what heap overflow vulnerabilities are and how they can be exploited. We'll also provide a proof-of-concept code example that uses scanf and malloc to demonstrate a heap overflow vulnerability.


What is a Heap Overflow Vulnerability?


A heap overflow vulnerability occurs when a program allocates memory from the heap and then writes more data than it can hold. This can cause a buffer overflow, which can be exploited by attackers to gain access to a system or execute malicious code. Heap overflows can be difficult to detect and exploit, but they can have serious consequences for an organization's security.


Heap overflows are caused by a combination of two factors: insufficient input validation and incorrect memory management. When a program allocates memory from the heap, it must ensure that the amount of memory allocated is sufficient to hold the data that will be written to it. If the program fails to do this, then a buffer overflow can occur when more data is written to the heap than it can hold.


Exploiting Heap Overflow Vulnerabilities


Exploiting heap overflow vulnerabilities is a complex process, but it can be accomplished with the right tools and techniques. The first step is to identify the vulnerable program and its heap layout. This can be done by inspecting the program's source code or by using a debugger to inspect the program's memory layout. Once the vulnerable program and its heap layout have been identified, the attacker must then craft an exploit that will trigger the heap overflow vulnerability.


The exploit should include a payload that will be written to the heap when the vulnerability is triggered. This payload can be used to execute malicious code or gain access to the system. It is important to note that the payload must be carefully crafted to ensure that it does not corrupt the heap or cause the program to crash.


Proof-of-Concept Code


Here is a proof-of-concept code example that demonstrates a heap overflow vulnerability using scanf and malloc. The code reads in a user-supplied string and then allocates memory from the heap to store the string. However, the amount of memory allocated is insufficient to hold the string, which causes a buffer overflow.



#include <stdio.h> 
#include <stdlib.h> 

int main(int argc, char *argv[]) { 
  char *buffer; 
  int size; 

  printf("Enter a string: "); 
  scanf("%s", buffer); 

  size = strlen(buffer); 
  buffer = (char *)malloc(size); 

  strcpy(buffer, argv[1]); 

  printf("String: %s\n", buffer); 

  free(buffer); 

  return 0; 
}


Conclusion


Heap overflow vulnerabilities are a type of memory corruption vulnerability that can have serious consequences for an organization's security. They are caused by a combination of insufficient input validation and incorrect memory management. Exploiting heap overflows can be a complex process, but it can be accomplished with the right tools and techniques. In this article, we have discussed what heap overflow vulnerabilities are and how they can be exploited. We have also provided a proof-of-concept code example that uses scanf and malloc to demonstrate a heap overflow vulnerability.



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