sprintf

sprintf is a function in the C programming language used for formatted output to a string. It's part of the C standard library and is used to compose a string with the same text that would be printed if the format string was used with printf, but instead of being printed, the content is stored in a string.

The syntax is:

int sprintf(char *str, const char *format, ...);
  • str: Pointer to a buffer where the resulting C-string is stored.
  • format: C string that contains a format string that follows the same specifications as printf.

The primary vulnerability associated with sprintf is buffer overflow. This occurs because sprintf does not perform bounds checking on the output buffer. If the formatted data exceeds the size of the buffer, it can overflow, overwriting adjacent memory, which can lead to undefined behavior, including crashing the program, corrupting data, or creating a security vulnerability.

An example of exploitation could be the following C program:

char buffer[50];
char *userInput = "Very long input string that exceeds 50 characters...";
sprintf(buffer, "Input: %s", userInput);

In this example, if userInput is longer than what buffer can hold, it will result in a buffer overflow. An attacker could exploit this by injecting code into userInput and using the overflow to overwrite a return address or other critical data in memory, potentially gaining control of the program's execution flow.

You should use safer variants like snprintf, which takes an additional parameter specifying the size of the buffer and ensures that the written string does not exceed this size:

snprintf(buffer, sizeof(buffer), "Input: %s", userInput)
  • Input Validation: Always validate the length and content of input before processing it.
  • Secure Coding Practices: Adopt secure coding practices and use modern programming languages or frameworks that provide safer alternatives and mitigate such risks.