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Comment by lxe | Hacker News Reader

What's the history behind this? I doubt there was legacy or backwards compat reasoning? Allowing for such a loose and wide interpretation makes for complicated parsing and numerous exploits.

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Most of the time it is just a banal shenanigans of strtoint conversions and how exactly the dotted decimal parser was written.

> for complicated parsing

Somewhat

> numerous exploits.

Nah. It's mostly localized to a string to hostname processing, ie it never occurs in the network stack and happens on the user'side of things and permissions (think CLI and interpreted languges)

not exploits of the OS, but I've used this to exploit web applications quite a bit. Tricks like these get your past a lot of input filters or validation logic. This allows me to trick these apps into making HTTP requests to internal or private IPs/hosts.

As an example, think of a cloud based web performance monitoring system. I trick it into making HTTP requests to 169.254.169.254, and I get access to data from their AWS metadata service...

Yep. Skipped this part (not at "he desktop RN) but honestly this is more in 'check what you accept' and input data validation|sanitation. Still a valid target for an exploit but you really need a bunch of things ('web performance monitoring system') to happen before you can have a meaningful usage (if at all) from these exploits.

I don't know about the hex representation, but the binary representation is useful for figuring out CIDR ranges

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