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Investigating an "evil" RJ45 dongle

(lcamtuf.substack.com)
289 points zdw | 4 comments | 17 Jan 25 20:41 UTC | HN request time: 0s | source
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MartijnBraam ◴[17 Jan 25 22:13 UTC] No.42743835[source]▶
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

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stavros ◴[17 Jan 25 22:45 UTC] No.42744057[source]▶
Hm, why does shorting CS and S0 make it not work?
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1. nick__m ◴[17 Jan 25 23:03 UTC] No.42744156[source]▶
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
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2. stavros ◴[17 Jan 25 23:10 UTC] No.42744214[source]▶
That makes sense, thank you.
3. cozzyd ◴[17 Jan 25 23:13 UTC] No.42744232[source]▶
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

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4. nick__m ◴[17 Jan 25 23:21 UTC] No.42744281[source]▶
Thanks you for refreshing my memory, I learn about that in college twenty-something years ago but never used that knowledge!