Null Byte Injection is a vulnerability where a null byte character (\0 or ASCII 0) is injected into user-supplied input to manipulate application behavior, often bypassing filters or terminating strings prematurely in languages like C or C++ that rely on null-terminated strings. In web applications, this is typically encoded in URLs using percent-encoding (e.g., %xx, where xx is the hexadecimal value). The ASCII value of a null byte is 0, which is represented as %00 in URL encoding.

Option A ("%01"): Represents the ASCII character with value 1 (Start of Heading), not a null byte.

Option B ("%10"): Represents the ASCII character with value 16 (Data Link Escape), not a null byte.

Option C ("%25"): Represents the % character itself (ASCII 37), not a null byte.

Option D ("%00"): Represents the null byte (ASCII 0), which is the correct URL-encoded form used in Null Byte Injection attacks.

The correct answer is D, aligning with the CAP syllabus under "Injection Attacks" and "Input Validation Bypasses."References: SecOps Group CAP Documents - "Null Byte Injection," "URL Encoding," and "OWASP Injection Prevention" sections.