During an on-site assessment of a chemical plant, you perform ARP spoofing to place yourself between the HMI and a Modicon PLC. You then craft a Modbus/TCP packet with function code 0x05 (Write Single Coil) that de-energizes the primary feed pump and send it directly to the PLC on TCP port 502. Which type of OT attack does this action exemplify?
Unauthorized command injection that causes denial-of-control over the process
Stuxnet-style code-signing bypass using Siemens Step7 protocol
PLC firmware replacement to upload malicious ladder logic
Man-in-the-middle manipulation causing loss-of-view by blocking telemetry responses
The tester is issuing an unsolicited Modbus/TCP control command that changes the state of a coil on the PLC. Because Modbus has no native authentication or encryption, any host on the same network segment can forge packets that appear to come from the trusted HMI. Injecting a Write Single Coil (0x05) command to turn a device off takes control away from operators and can halt the process. This is classified as an unauthorized command injection that results in a denial-of-control effect.
Blocking telemetry (loss-of-view) would require suppressing or altering replies rather than issuing a control write. Firmware replacement targets the PLC's operating code, not individual I/O points. A Step7 code-signing bypass is specific to Siemens S7 equipment and is unrelated to Modbus command spoofing.
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What is Modbus/TCP and why is it significant for OT security?
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What is ARP spoofing and how does it enable man-in-the-middle attacks?
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How does unauthorized command injection specifically affect OT systems?
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What is ARP spoofing and how does it allow an attacker to intercept communication?
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What is Modbus/TCP and why is it considered insecure?
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Why is the Write Single Coil (function code 0x05) command significant in this attack?
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