After three months of development, OpenSSH 10.4, an open-source client and server implementation for the SSH 2.0 and SFTP protocols, has been released. Key changes include:
- Experimental support has been added for the "mldsa44-ed25519" combined digital signature generation scheme, which combines the ML-DSA 44 post-quantum algorithm and the Ed25519 elliptic curve algorithm. To enable support, add "mldsa44-ed25519" to the HostKeyAlgorithms and PubkeyAcceptedAlgorithms directives. To generate keys, use the "ssh-keygen -t mldsa44-ed25519" command.
- ssh and sshd use a new implementation of the pattern matching system, which is based on a non-deterministic finite state machine and is not subject to the problem of exponential growth of computational complexity when using masks containing many '*' characters.
- Changed behavior Linux- sshd builds with enabled system call filtering using seccomp. Previously, a crash occurred when activating SECCOMP or NO_NEW_PRIVS on Linux-on systems without their support, it would cause a warning to be written to the log and work to continue without isolation, but now it will cause a crash.
- When using the "sshd -G" option in the configuration dump, directives are now written using uppercase and lowercase letters, instead of only lowercase letters (i.e. "PubkeyAuthentication" instead of "pubkeyauthentication").
- The behavior of ssh and sshd has been adjusted to comply with RFC 4253: sending messages unrelated to the key exchange during a key re-exchange will now result in the connection being terminated. Previously, attackers could perform a DoS attack by endlessly sending third-party messages during the key exchange, which were buffered on server and wasted memory.
Several security issues have been fixed:
- The ssh utility has been fixed to address a potential use-after-free issue when accessing malicious code. serverThe issue is exploited by changing the host key during the key re-exchange process.
- A vulnerability in SFTP allows a file to be uploaded to another directory when accessing a malicious server using a command in the form "sftp host:/path ."
- A vulnerability in scp allows, when copying files between two external servers, one of which is controlled by the attacker, organize the writing of files to the parent directory, located one level below the target directory.
- Fixed an issue in sshd that occurred when using the internal SFTP server implementation ("internal-sftp"), which is disabled by default. The issue relates to the truncation of long command-line sequences after the 9th argument, leading to subsequent arguments being discarded. This could potentially result in security-related options being discarded.
- A bug in sshd has been fixed due to which the "DisableForwarding=yes" directive did not disable the ability to create tunnels permitted by the "PermitTunnel=yes" option (not set by default).
- Fixed an issue in sshd that could be exploited to initiate a denial of service during the pre-authentication phase when the GSSAPIAuthentication directive is enabled in the settings (disabled by default). This issue is not blocked by the "MaxAuthTries" limit, but is covered by the "PerSourcePenalties" limit.
- Fixed a bug in sshd that prevented the minimum delay between authentication attempts from always being added.
Source: opennet.ru
