- Update to 3.4.0: (CVE-2023-48795, bsc#1218168)
* Transport grew a new packetizer_class kwarg for overriding the
packet-handler class used internally.
* Address CVE 2023-48795 (aka the "Terrapin Attack", a vulnerability found
in the SSH protocol re: treatment of packet sequence numbers) as follows:
+ The vulnerability only impacts encrypt-then-MAC digest algorithms in
tandem with CBC ciphers, and ChaCha20-poly1305; of these, Paramiko
currently only implements hmac-sha2-(256|512)-etm in tandem with
AES-CBC.
+ As the fix for the vulnerability requires both ends of the connection
to cooperate, the below changes will only take effect when the remote
end is OpenSSH >= 9.6 (or equivalent, such as Paramiko in server mode,
as of this patch version) and configured to use the new
"strict kex" mode.
+ Paramiko will now raise an SSHException subclass (MessageOrderError)
when protocol messages are received in unexpected order. This includes
situations like receiving MSG_DEBUG or MSG_IGNORE during initial key
exchange, which are no longer allowed during strict mode.
+ Key (re)negotiation -- i.e. MSG_NEWKEYS, whenever it is encountered --
now resets packet sequence numbers. (This should be invisible to users
during normal operation, only causing exceptions if the exploit is
encountered, which will usually result in, again, MessageOrderError.)
+ Sequence number rollover will now raise SSHException if it occurs
during initial key exchange (regardless of strict mode status).
* Tweak ext-info-(c|s) detection during KEXINIT protocol phase; the
original implementation made assumptions based on an OpenSSH
implementation detail.