DSA-5588-1 putty – security update

Debian Security Advisory

Fabian Baeumer, Marcus Brinkmann and Joerg Schwenk discovered that the
SSH protocol is prone to a prefix truncation attack, known as the
“Terrapin attack”. This attack allows a MITM attacker to effect a
limited break of the integrity of the early encrypted SSH transport
protocol by sending extra messages prior to the commencement of
encryption, and deleting an equal number of consecutive messages
immediately after encryption starts.

Details can be found at https://terrapin-attack.com/