How to break WiFi on an HP OfficeJet Pro 8740
Hint: it’s as simple as enabling 802.11r!
This article is for my own future reference, although perhaps it will help you, in a somewhat bizarre set of circumstances.
I recently changed my WiFi networks (moving all IoT devices to their own SSID and VLAN). When I finally went to update my printer’s WiFi settings, it incorrectly listed my SSIDs as “unsecured,” and “open authentication.” This was certainly false; like most home SSIDs, mine used WPA2 Personal. Sigh.
A quick Google search yielded nothing — like most issues I encounter, they are usually specific and uncommon enough that nobody else has answered them or at least described them well enough for the report to show up in search results.
Alas, I am a wireless engineer. I knew that the security settings that appear for an SSID are broadcast as part of the “beacon” frame — read more here if you’re interested — and some (legacy or otherwise poorly designed) wireless clients have issues dealing with unexpected information within beacon frames. So, for my troubleshooting, I was interested in what beacon settings I could configure on my wireless AP, which, in this case, was a Unifi AP.
Upon examining these settings, I saw that “Enable fast roaming” was enabled. “Fast roaming” can mean different things on different WiFi vendors, but it usually means 802.11r information is added to the SSID beacons to speed up a specific type of client device roaming, usually related to SSIDs that employ 802.1x/RADIUS (also known as WPA2 Enterprise) authentication. This is indeed what it means on Unifi APs. And even if I were using RADIUS auth — which the HP printer does support — this is an IoT network. The devices are fairly static; they don’t have much occasion to roam. How often am I going to relocate this printer, anyway?
In short, it’s wholly unnecessary to enable 802.11r for most IoT-specific networks, so I disabled it. And voilà — the HP printer’s wireless setup wizard finally (correctly) showed that my IoT SSID was secured, and successfully joined the network.
The takeaway here, as far as I’m concerned, is HP needs to fix their printers’ wireless drivers so that they properly handle 802.11r, among other beacons.
