The release of OpenSSH 9.0 is presented, an open implementation of the client and server for working with the SSH 2.0 and SFTP protocols. In the new version, the scp utility has been moved by default to use SFTP instead of the legacy SCP/RCP protocol.
SFTP uses more predictable name handling methods and does not use shell processing of glob patterns in filenames on the other host side, which creates security problems. In particular, when using SCP and RCP, the server decides which files and directories to send to the client, and the client only checks the correctness of the returned object names, which, in the absence of proper checks on the client side, allows the server to transfer other file names that differ from those requested.
The SFTP protocol does not have these problems, but does not support the expansion of special paths such as β~/β. To eliminate this difference, starting from OpenSSH 8.7, the SFTP server implementation supports the protocol extension "[email protected]' to expand the ~/ and ~user/ paths.
When using SFTP, users may also encounter incompatibilities caused by the need to double-escap path expansion characters in SCP and RCP requests to prevent them from being interpreted on the remote side. In SFTP, this escaping is not required, and extra quotes can result in a data transfer error. At the same time, the OpenSSH developers refused to add an extension to repeat the behavior of scp in this case, since double escaping is considered as a flaw that does not make sense to repeat.
Other changes in the new release:
- ssh and sshd have hybrid key exchange enabled by default "[email protected]Β» (ECDH/x25519 + NTRU Prime), resistant to pickup on quantum computers and combined with ECDH/x25519 to block possible problems in NTRU Prime that may surface in the future. In the KexAlgorithms list, which determines the order in which the key exchange methods are chosen, the mentioned algorithm is now ranked first and takes precedence over the ECDH and DH algorithms.
Quantum computers have not yet reached the level of cracking traditional keys, but the use of hybrid protection will protect users from attacks related to storing intercepted SSH sessions in the expectation that they can be decrypted in the future, when the necessary quantum computers become available.
- The "copy-data" extension has been added to sftp-server, which allows copying data on the server side, without passing it to the client, if the source and destination file are on the same server.
- The "cp" command has been added to the sftp utility to initiate file copying on the server side by the client.
Source: opennet.ru