TCP: Treason uncloaked!

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Once in a while I get the following message in my dmesg output:

TCP: Treason uncloaked! Peer [some ipaddress]:6011/80 shrinks window 2823933880:2823935165. Repaired.

There are loads of discussions on the internet about the harmlessnessity of this logrecord. There is a camp of people discussing as complete harmless. Just some misconfiguration of the remote system. On the other side of the harmlessness spectrum, people discuss this record as an attempt to attack the system. Let’s figure this out…

Cause of the message.