The most likely way a rogue device was able to connect to the network is through a MAC cloning attack. In this attack, a personal device copies the MAC address of an authorized device, bypassing the 802.1X access control that relies on known hardware addresses for network access. The matching MAC addresses in the audit report suggest that this technique was used to gain unauthorized network access.

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CompTIA Security+ SY0-701 Course Content: Domain 03 Security Architecture​.

CompTIA Security+ SY0-601 Study Guide: Chapter on Network Security and MAC Address Spoofing​.