Hello,
accedently I found a message having 8 DKIM signatures. My DKIM
verifier (OpenDKIM) wrote a log "ignoring 2 signatures". Challenge
accepted! I also found "ignoring 53 signatures"! *)
The number of messages having *many* DKIM signatures is very low. But
the exist.
And for that reason it's good to have a limit like this:
https://manpages.debian.org/trixie/opendkim/opendkim.conf.5.en.html#MaximumSignaturesToVerify
This is also mentioned in RFC 6376, Section 4.2
To limit potential denial-of-service attacks, Verifiers MAY limit the total
number of signatures they will attempt to verify
Have a minute to check that your DKIM validation implementation have
limits implemtent and activated ...
Andreas
*) just in case you follow my data and check the defaults: I've set
MaximumSignaturesToVerify to 6
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