Not sure what it is, but it looks similar to aloe mite - I do not know if other plants get infected with it or not. Hopefully someone knows...

Eta: here is a link to article from Dave's Garden describing Aloe mite/Aloe cancer.

I agree with Rina. Not Aloe mite but one just for euphorbia. Most mites are species specific. Not an expert, just guessing. Keep the whole plant away from your other plants until you find out. The cure is much more costly and troublesome than just disposing of the plant in question. I would cut that section off and see if any thing comes out form it. Mostly it is all thru the plant. Did you just get this plant? It is possible the supplier has a bigger problem than you do.

I saw aloe mite infested in one aloe in a nursery that a person almost bought thinking it was some thing special. I informed them and the owner removed the whole tray and would not sell any. I believed he trashed them in the dumpster. He did know about aloe mites.

Not Aloe mites as they are specific to Aloe and Haworthia only. I would say mites look to be the culprit here too. Quarantine ASAP and you should identify the type of mite it is to know what miticide to use (if you have other affected plants).