HawkScan Test Info for Format String Error

Format String Error


Plugin Id: 30002 | CWE: 134


To mitigate the risk of a Format String error, the following measures can be taken:

  1. Input validation: Implement strict input validation to ensure that user-supplied data is properly formatted and does not contain any malicious characters or commands. This can be achieved by using input validation functions or regular expressions to validate and sanitize user input.

    Example in Python:

    import re
    def validate_input(input_string):
        if re.match(r'^[a-zA-Z0-9\s]+$', input_string):
            # Valid input
            return True
            # Invalid input
            return False
  2. Output formatting: Use proper formatting functions or libraries to ensure that user-supplied data is correctly interpreted and displayed. Avoid using format string functions that allow the evaluation of user input as commands.

    Example in C:

    #include <stdio.h>
    int main() {
        char user_input[100];
        printf("Enter your name: ");
        scanf("%s", user_input);
        // Incorrect usage of format string
        return 0;
  3. Secure coding practices: Follow secure coding practices and guidelines to minimize the risk of Format String errors. This includes using secure coding frameworks, avoiding the use of unsafe functions, and regularly updating and patching software to address any known vulnerabilities.


A Format String error occurs when the submitted data of an input string is evaluated as a command by the application. This vulnerability arises when an application does not properly validate or sanitize user-supplied input before using it as a format string. Attackers can exploit this vulnerability to manipulate the format string and execute arbitrary code or leak sensitive information from the application’s memory.

Format String errors can occur in various programming languages and are commonly found in C, C++, and languages that use similar format string syntax. These vulnerabilities can lead to serious security breaches, including remote code execution, information disclosure, and denial of service attacks.


The risks associated with Format String errors include:

  • Arbitrary code execution: Attackers can craft malicious format strings that exploit the vulnerability to execute arbitrary code within the application’s context. This can lead to complete compromise of the system and unauthorized access to sensitive data.

  • Information disclosure: By manipulating the format string, attackers can leak sensitive information from the application’s memory, such as passwords, encryption keys, or database credentials. This can result in unauthorized access to critical systems or data breaches.

  • Denial of service: Format String errors can be exploited to crash the application or consume excessive system resources, leading to a denial of service condition. This can disrupt the availability of the application and impact the overall system performance.