CPENT Iot And OT Exploitation Practice Question
An OT security engineer is conducting a vulnerability assessment on a Distributed Control System (DCS). The engineer needs to test for unauthorized firmware write capabilities on a legacy controller using the Modbus protocol. Which Modbus function code is typically associated with writing multiple holding registers, which could be abused to modify configuration parameters?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Function Code 16 (0x10) - Write Multiple Registers
Modbus function codes define the action to be performed. Function Code 16 (0x10) is 'Write Multiple Registers', frequently used to change register blocks in industrial controllers.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Function Code 01 (0x01) - Read Coils
Why it's wrong here
Function Code 01 is a read-only operation used to read the status of binary outputs (coils).
- ✗
Function Code 04 (0x04) - Read Input Registers
Why it's wrong here
Function Code 04 is a read-only operation used to retrieve analog input values.
- ✗
Function Code 02 (0x02) - Read Discrete Inputs
Why it's wrong here
Function Code 02 is a read-only operation used to read the status of binary inputs.
- ✓
Function Code 16 (0x10) - Write Multiple Registers
Why this is correct
Function Code 0x10 allows writing blocks of holding registers, which often control setpoints, operational parameters, and logic variables.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official EC-Council exam blueprint
This CPENT practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CPENT exam.