I came across the tweet about this "Evil" dongle and instantly recognized it as the exact same thing I worked on before... It's not evil, it's just annoying.
https://blog.brixit.nl/making-a-usb-ethernet-adapter-work-sr...
In my case I disabled the SPI flash module to have it not appear as a CD drive, the author of this post actually found some documentation about the SPI being optional. Funnily enough this post now also gives you all the tooling to make an actual evil RJ45 dongle by reflashing one :D
What happened to U3 at the top left in the image of the flash chip?
Looks like they had a footprint for a diode in a 3-pin SOT23 package and found they didn't have stock of the special part, so they installed a SOD323 diode at a 30 degree angle across two pins...
Hm, why does shorting CS and S0 make it not work?
Shorting almost any two of the communication lines of the flash chip will corrupt the communication enough that the ethernet controller thinks there's no flash installed at all.
I have no idea about S0 but CS is usually chip select. It should be sufficient to short it to prevent the chip from being selected. However CS is frequently inverted and you would have to pull it up to prevent the chip selection, so maybe S0 is always high and inhibit CS
SO (MISO) should generally be high impedance if not selected...
I suspect this causes SO to always output the same value and the Ethernet controller must expect some magic
Thanks you for refreshing my memory, I learn about that in college twenty-something years ago but never used that knowledge!