GIAC Foundational Cybersecurity Technologies Practice Test

What defines a Format String Vulnerability?

1. Using a format string incorrectly in programming

2. Running printf in C without a format string

3. Passing an incorrect format parameter in output functions

4. Failing to validate input for formatting functions

The correct answer is: Running printf in C without a format string

The correct definition of a Format String Vulnerability revolves around the misuse or incorrect application of format strings, particularly in programming languages like C. A Format String Vulnerability occurs when an attacker is able to manipulate the format string argument used in functions that handle formatted output, such as `printf`. This vulnerability typically arises when user input is improperly allowed as a format string. For instance, if input from a user is directly inserted into a function call expecting a format string without proper validation or sanitation, an attacker can exploit this to execute arbitrary code, read memory addresses, or manipulate the program’s execution flow. The notion that running `printf` in C without a format string characterizes a Format String Vulnerability is misleading, as this would simply lead to undefined behavior or runtime errors rather than exploiting the application's logic or unintended behavior. Gathering context from the other options, using a format string incorrectly may not suffice to classify a vulnerability unless it includes user input manipulation. Furthermore, incorrectly passing a format parameter in output functions may hint at programming errors, but that does not encompass the exploitation potential characteristic of Format String Vulnerabilities. Failing to validate input for formatting functions is relevant but primarily addresses the root cause rather than defining the nature of the vulnerability itself.