The release of OpenSSH 9.9 has been published, an open implementation of the client and server for working with SSH 2.0 and SFTP protocols. Key changes include:
- Support for the hybrid key exchange algorithm "mlkem768x25519-sha256" has been added to ssh and sshd, which is resistant to quantum computer attacks and consists of a combination of X25519 ECDH and the ML-KEM algorithm (CRYSTALS-Kyber), recently standardized by the National Institute of Standards and Technology (NIST). ML-KEM utilizes cryptographic methods based on solving lattice theory problems, for which the solving time is unaffected by whether the computers are classical or quantum.
- The configuration file sshd_config has been updated with the keyword "RefuseConnection", whereby sshd will terminate connections after the first authentication attempt. The directive PerSourcePenalties has been augmented with the class "refuseconnection", which is applied when terminating connections after the "RefuseConnection" trigger.
- Support for data compression before authentication has been discontinued in the ssh client, significantly reducing the attack surface on SSH servers and mitigating the risks of indirect methods of information analysis during the authentication process. In server sshd, compression before authentication was disabled earlier.
- In ssh and sshd, parsing of arguments for the "Match" directive now employs shell-like rules for handling quoted strings, supporting nested quoting and escaping using the "\" character.
- The ssh_config configuration file has introduced support for environment variables and "%" substitutions in the "Include" directive, similar to the behavior in the "Match Exec" directive.
- The Match directive in sshd_config has added the option "invalid-user", which activates when an entry attempt is made with an incorrect username.
- A faster implementation of the algorithm "Streamlined NTRUPrime" is now utilized in ssh and sshd. For the hybrid key exchange algorithm Streamlined NTRUPrime/X25519, the option to use the name "sntrup761x25519-sha512" has been added, in addition to the SSH-specific name "sntrup761x25519-sha512@openssh.com".
- In ssh, sshd, and ssh-agent, a safeguard against the dumping of private keys in core files has been added, which works on OpenBSD, Linux, and FreeBSD.
- Key processing has been transitioned to utilize the EVP_PKEY API provided by the libcrypto library.
- A random change of the connection timeout (LoginGraceTime) within 4 seconds has been added to sshd to complicate timeout identification.
- Issues with building against the Musl library have been resolved.
Source: opennet.ru
