Cisco’s 'intuitive security' tool can’t handle MAC address randomization out-of-the-box

iOS 14's new MAC scrambling could stop upgraded devices from connecting, Android 10 also a mess

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Cisco promotes its Identity Services Engine (ISE) as “intuitive network security for the digital age.” But Switchzilla has just explained that it’s not very good at handling the growing practice of MAC address randomization by mobile devices.

A refresher: MAC addresses are unique identifiers assigned to network interface controllers, and are disclosed when devices communicate with each other on a network. MAC addresses were developed in more innocent times before we all started carrying networked devices around with us, and that they promiscuously probe Wi-Fi hotspots and Bluetooth gizmos prior to initiating connections. Those probes, and human-initiated connections, are often made without regard for the fact that it’s possible to track a device through space by following its MAC address from network to network.

The tech world wised up to this, and started to program devices to periodically randomize their MAC addresses when probing so that the handhelds stopped leaving such easy-to-follow breadcrumb trails. This probing technique appeared in version 8 of both iOS and Android, in 2014 and 2017 respectively. Android 10 added MAC address randomization for all network activities in 2019; iOS 14 added it this week. Windows 10 has had it for a while, too.

Which brings us to September 15, 2020, when Cisco disclosed in a field notice that “Identity Services Engine MAC Address Lookup Might Fail with Android 10 and Apple iOS 14 Devices Due to the Use of MAC Randomization on the Mobile Client Devices.”

The field notice explains that unless ISE is fed policies to handle MAC address randomization, “previously provisioned mobile devices and the policies configured based on profiling identity groups might be incorrectly matched after the new MAC address randomization behavior takes effect.

“This could result in network connectivity disruption for these mobile devices.”

Cisco explains the cause of the problem as follows:

Even though the Android 10 and iOS 14 devices are set up to use randomized MAC addresses, when a wireless profile is created on the device the MAC address is always generated with the same random MAC address for the given wireless profile. This is true even when the wireless profile is deleted and recreated. However, when the dual-SSID BYOD flow is used, different MAC addresses will be generated for the onboarding SSID and the secured SSID. This causes a policy mismatch when using the precreated ISE BYOD Employee_EAP-TLS authorization rule.

This also impacts the single-SSID BYOD flow for devices that have been onboarded while running a previous version of iOS. Prior to iOS 14, the device uses a real MAC address for wireless access. However, upon upgrade to iOS 14, all existing wireless profiles will be updated to use random MAC addresses. Since the MAC address used during the previous version of iOS and after iOS 14 is different, authentication might fail if MAC address related conditions are used in conjunction with BYOD.

iOS 14, which became available today, therefore seems to be a part of the problem. But not all of it because ISE has offered MAC randomization workarounds in March 2020 prior to version 14's official release.

Cisco’s latest field notice advises: “There is currently no large scale solution for the issues introduced by third-party MAC address randomization, only workarounds are available.” That workaround is detailed in the field notice, and has five steps; it doesn’t look horribly onerous.

The Register leaves it to our readers to decide if the need for a workaround represents “intuitive network security for the digital age.” ®

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