- A compression pointer is when the two higher bits are set, the code was
considering only 0xC0 as a pointer, where in reality anything from 0xC0-0xFF is
a pointer, probably went unnoticed since you need big packets to have long pointers.
- Make sure we can access the lower byte of the pointer by checking len, the
code was careful to not access past the first byte, but ignored the second.
- As per RFC9267 make sure a pointer only points backwards, this one is not so
bad, as the code had a iteration_max that ended up guarding against infinite jumps.
Lightly tested, some eyes are welcome, but these are remote DOSable.
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