[TUHS] [SPAM] Re: SCCS
dave at horsfall.org
Sat Sep 14 08:30:42 AEST 2019
On Fri, 13 Sep 2019, Norman Wilson wrote:
> UDP (and TCP) checksums are nearly useless against the sort of
> corruption Larry described. Since they are a simple addition with carry
> wraparound, you can insert or remove any number of word-aligned pairs of
> zero octets without the checksum changing.
I was thinking of an intermediate router (probably one that you never knew
about) corrupting the checksum-less UDP packet, recalculating the Ethernet
checksum, and your kernel happily accepting it; you now have an
application that fails for some unknown reason.
Never seen it in practice, but I've heard of it happening.
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