During a red team engagement, an ethical hacker discovers that a thermostat accepts older firmware...

CEH v13 emphasizes that IoT devices must implement secure firmware update mechanisms that enforce authenticity, integrity, and version control. A critical lapse occurs when devices allow rollback to older firmware versions or accept updates without cryptographic validation. This opens the door to “firmware downgrade attacks,” where attackers intentionally install outdated but vulnerable firmware to reintroduce exploitable weaknesses. CEH identifies this as part of insecure update design, one of the most dangerous IoT vulnerabilities because firmware governs device behavior, network communication, and trust boundaries. Without signature verification, integrity checking, and anti-rollback enforcement, attackers can load malicious or deprecated firmware to escalate privileges or pivot deeper into a network. Options B and C represent different categories of IoT weaknesses, and D refers to supply-chain issues, none of which match the described rollback exploitation. Therefore, the vulnerability demonstrated is the absence of secure update mechanisms.