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Comment by JSDevOps | Hacker News Reader

Unless it’s satire and I’ve missed the point. I'd have thought this wouldn't physically be possible because of the OSI model.

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For more context, read the comment[0] on Reddit's /r/sysadmin thread from the follow-up tweet[1]. It boils down to a certain bit-pattern in the spreadsheet's headers that corresponded to a signalling pattern in their T1 line, around the year 2003, causing the T1 equipment to fail.

[0] (2018) https://old.reddit.com/r/sysadmin/comments/9si6r9/postmortem...

[1] https://twitter.com/lauriewired/status/1838257118685921694

Oh, it's entirely possible in principle (I don't know about the details of T1 in this specific case).

Many years ago, there used to be a vulnerability with a lot of modems where you could send a ping packet to a machine connected via dialup, and the machine would send back a response that its modem would interpret as telling it to hang up the call: https://seclists.org/bugtraq/1998/Sep/192

The OSI model is an abstraction that can be broken by implementation bugs or design flaws, not an immutable law of the universe.

EDIT: I see that some of the Twitter replies beat me to mentioning this.

Hayes figured out how to make that impossible: The "guard time" interval. When you want to interact with the modem, you have to send _nothing_, not a single character, for a whole second before sending +++ and then another whole second of nothing. Only then would the modem place you into command mode. That way, +++ could happily appear in payload but never mess with the modem, because there'd be other payload either side of it.

Of course they patented this, and anyone who licensed the patent was likewise immune, but the manufacturers who didn't, could easily be plonked like this.

My first "hack" involved a BBS scripting language that involved a delay command... ;)

Repeated patterns in digital signals can cause errors in several ways such as DC bias (likely the case here), or a buildup of energy on the edges of the signal's fourier spectrum which then gets filtered out and shows up as signal degradation on the oscilloscope.

Nowadays the lower layer transmission protocols all re-code the signal to ensure frequent edge transitions, and after a few layers of that the odds of these patterns causing problems goes way down.

And then compression and encryption (hopefully in that order!) make it go away entirely.

Buuut, 25 years ago network equipment wasn't as layered and sophisticated as it is today, so that sort of thing would crop up now and then.

OSI model makes it more possible. After all for each layer anything above it is just well bits... And if some layer is poorly implemented it can interpret certain run of bits as something else and act accordingly, but wrong.

There is lot of bad code specially when you have multiple implementations and all doing their own thing on their own level.

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