An intruder might exploit a buffer-overflow weakness to manipulate a program that is expecting input from the user. Buffer overflows can manifest as either heap-based or stack-based vulnerabilities.
Heap-based assaults focus on applications by overflowing the reserved memory area for a program, making them less common than stack-based attacks and more difficult to execute. Adversaries commonly exploit stack-based buffer overflows to target programs and applications, leveraging the stack's memory allocation for storing user input.
Let's explore real code samples that demonstrate the risks involved in such situations using the C programming language.
In the examples provided, we illustrate the potential for buffer overflow without actually incorporating any harmful code injection practices. Contemporary compilers commonly incorporate overflow checking capabilities at compile/link time. Nonetheless, validating this vulnerability at runtime proves to be a formidable task without supplementary safety measures such as employing exception handling.
Example:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
// Reserve 5 bytes for the buffer, plus the NULL at the end.
// should allocate 2 double words (8 bytes)
// Need more than 8 bytes to overrun...
char buffer[5]; // If the user enters more than 8 characters, there will be an access violation and a segmentation fault.
// a prompt how to execute the program...
if (argc < 2)
{
printf("strcpy() NOT executed....\n");
printf("Syntax: %s <characters>\n", argv[0]);
exit(0);
}
// copy the user input to mybuffer, without any
// bound checking a secure version is strcpy_s()
strcpy(buffer, argv[1]);
printf("buffer content= %s\n", buffer);
// you may want to try strcpy_s()
printf("strcpy() executed...\n");
return 0;
}
Output:
If input :- 12345678 (8 bytes)
Then o/p;- the program run smoothly.
If input:- Input : 123456789 (9 bytes)
Then o/p;- "Segmentation fault" message will be displayed and the program terminates.
Explanation:
In this particular scenario, the security weakness arises when the size of the input provided by the user ( argv[1] ) exceeds 8 bytes, potentially leading to a buffer overflow. To fully utilize a 32-bit (4 bytes) system, we must occupy a full double word's worth of memory, which is 32 bits or 4 bytes. Given that each character (char) occupies one byte, if we request a buffer of 5 bytes, the system will allocate memory space equivalent to two double words (8 bytes). This allocation mismatch is the reason why the mybuffer becomes susceptible to overflow when input surpasses 8 bytes.
There are common functions such as strncpy, strncat, and memcpy that are similar but more resilient. The drawback of these functions is that the developer needs to specify the buffer size instead of relying on the compiler.
Prior to commencing programming tasks, it is imperative for any C/C++ developer or programmer to have a thorough understanding of the buffer overflow vulnerability. This particular issue can result in the generation of numerous flaws, some of which may be susceptible to exploitation.
What Happens During a Buffer Overflow Attack?
A buffer overflow assault frequently entails a hacker altering memory beyond a buffer to exploit a software vulnerability. Below is a summary of how this type of attack may transpire:
Insecure Code:
The assailant identifies a vulnerability in the code of the target program. This code could include functions associated with user input, such as gets and strcpy, which fail to validate input boundaries.
Entering Data:
The attacker surpasses the allocated memory of the buffer with their input data. For example, when a buffer has a capacity for 50 characters, the attacker submits 60 characters or beyond.
Data overwriting:
The software fails to validate the boundaries prior to accepting input from a potential attacker into the buffer. As a result, there is a risk of overflowing the buffer with extra data, potentially corrupting important data such as function pointers, return addresses, or other variables located in adjacent memory locations.
Exploitation:
The aggressor has the ability to impact the behavior of a program by meticulously crafting the input data. For example, they could replace an address linked to harmful code they plan to execute for a function pointer.
Execution of Malicious Code:
The software could potentially execute the attacker's script upon reaching the altered return address or activating the adjusted function pointer, leading to unapproved entry, privilege elevation, or other harmful activities.
Conclusion:
C buffer overflow exploits can cause severe damage, making them a significant concern for developers and cybersecurity professionals. Safeguarding against these exploits requires understanding their mechanisms and implementing preventive measures like using secure functions, validating buffer sizes, and leveraging security utilities.
Safeguarding the authenticity and protection of software systems in today's dynamic landscape of cybersecurity risks hinges on staying informed about top practices and security protocols. It is imperative for developers to give precedence to secure coding methods and consistently enhance their expertise to defend against emerging threats such as buffer overflow assaults.