Openssh has recently published the release of OpenSSH 9.9, which includes updates for both client and server applications working with SSH 2.0 and SFTP protocols. The main changes are as follows:
- SSH and SSHD have added support for the hybrid key exchange algorithm “mlkem 76×25519-Sha256“, which is resistant to quantum computer attacks. This algorithm combines X25519 ECDH and the ml-kem (Crystals-Kyber) algorithm standardized by NIST.
- The “Refuseconnection” keyword has been added to the SSHD_Config configuration file to terminate connections after the first authentication attempt. The Persourcepenalties directive now includes the “RefuseConnection” class for this purpose.
- Data compression in the SSH client now stops before authentication, increasing server attack surface. Compression before authentication was already disabled in the SSHD server.
- Match directives in SSH and SSHD now support working with lines enclosed in quotation marks, allowing for investment framing and shielding using “”.
- The Include directive in SSH_CONFIG now supports environment and “%” substitutions similar to the “Match Exec” directive.
- In SSHD_Config, the “Invalid-User” option has been added to the Match directive to handle incorrect username entry attempts.
- Faster implementation of the “Streamline Ntruprime” algorithm has been introduced in SSH and SSHD. The ability to use the name “SNTRUP761x2519-SHA512” for key exchange in addition to “[email protected]” has been included.
- Protection against setting up closed keys in Core-files has been added to OpenBSD, Linux, and FreeBSD for SSH, SSHD, and SSH-Agent.
- Key processing now utilizes the API EVP_PKEY from the libcrypto library.
- SSHD now includes a random change in connection timeout (logingracetime) within a 4-second
/Reports, release notes, official announcements.