[maurice2k]

the problem is that most people do not monitor heavy use of TXT records; it's rather A/AAAA resolves in my experience.

but most production system i've seen allow all outgoing traffic (if poorly managed) or restrict it to port 443 (for some APIs) which is kind of all.

so if you're not in a very very restricted system (and then DNS should be restricted as well!) you'll most likely find an easy way to copy stuff over HTTPS.

[sgjohnson]

You could also use AAAA records to exfil data. Whole 128 bits at a time.

Of course there are far more practical ways of going about it.

[hnlmorg]

CNAME too. I dont know what the max field length for CNAME is though.

[comprev]

between 1 and 63 characters I think is the min/max

[wiml]

63 bytes per label, but the name can be longer than that.