lftp says “DH GEX group out of range”

I use lftp in a launchctl script to transfer and delete files from an Axway/Tumbleweed secure server, but after upgrading to macos Sierra, the connection failed (and looped forever retrying) with a brief flash of a “DH GEX group out of range” message. Searching for the message reveals that it’s an ssh issue (DH is diffie-hellman): Apple […]