After three months of development, OpenSSH 10.4 has been released, an open implementation of the client and server for operation over SSH 2.0 and SFTP protocols. Key changes:
- Experimental support for a combined digital signature scheme 'mldsa44-ed25519' has been added, combining the post-quantum algorithm ML-DSA 44 with the elliptic curve-based Ed25519 algorithm. To enable support, add 'mldsa44-ed25519' to the HostKeyAlgorithms and PubkeyAcceptedAlgorithms directives. You can use the command 'ssh-keygen -t mldsa44-ed25519' to generate keys.
- A new implementation of the pattern matching system has been introduced in ssh and sshd, based on a non-deterministic finite automaton that is not affected by the exponential growth of computational complexity when using masks containing many '*' characters.
- The behavior of the Linux builds of sshd with system call filtering enabled via seccomp has been changed. Previously, a failure when activating SECCOMP or NO_NEW_PRIVS on Linux systems that do not support them would result in a logged warning and continue running without isolation, but now it will cause a crash.
- When using the 'sshd -G' option in the configuration dump, directives are now recorded using both uppercase and lowercase letters, instead of being recorded only in lowercase letters (i.e., 'PubkeyAuthentication' instead of 'pubkeyauthentication').
- The behavior of ssh and sshd has been brought in line with RFC 4253: sending messages unrelated to key exchange during a key re-exchange will now result in the connection being terminated. Previously, attackers could carry out a DoS attack by continually sending unrelated messages during key exchange, which were buffered and server used memory.
Several security issues have been resolved:
- In the ssh utility, a potential use-after-free memory access issue has been fixed when accessing a malicious server. The issue is exploited by changing the host key during the key re-exchange.
- A vulnerability in sftp allows uploading a file to a different directory when accessing a malicious server using a command in the form 'sftp host:/path .'.
- A vulnerability in scp allows copying files between two external serversone of which is under the attacker's control, to organize file writing in the parent directory located one level below the target directory.
- The issue in sshd that manifested when using the internal implementation of the SFTP server ('internal-sftp'), which is disabled by default, has been resolved. The issue was related to truncating long sequences in the command line after the 9th argument, leading to subsequent arguments being discarded. Thus, potential options related to security could have been omitted.
- The sshd flaw has been fixed, which caused the directive 'DisableForwarding=yes' not to disable the ability to create tunnels allowed by the 'PermitTunnel=yes' option (which is not set by default).
- An issue in sshd has been fixed that could be used to initiate a denial of service before authentication when the GSSAPIAuthentication directive is enabled in the settings (disabled by default). The problem is not blocked by the 'MaxAuthTries' limit but falls under the 'PerSourcePenalties' restriction.
- Fixes have been made in sshd to ensure that a minimal delay is not always added between authentication attempts.
Source: opennet.ru
