Download OpenSSH 8.0

OpenSSH encrypts network traffic to prevent eavesdropping, connection hijacking, and other network attacks. In addition, it includes the ability to set up so-called secure tunnels and supports various authentication methods. OpenSSH is primarily developed for OpenBSD, users of other operating systems can here justly. The developers have released version 8.0 of OpenSSH with the following announcement:

OpenSSH 8.0 released

OpenSSH 8.0 was released on 2019-04-17. It is available from the mirrors listed at OpenSSH is a 100% complete SSH protocol 2.0 implementation and includes sftp client and server support. Once again, we would like to thank the OpenSSH community for their continued support of the project, especially those who contributed code or patches, reported bugs, tested snapshots or donated to the project. More information on donations may be found at: http://www.openssh.com/donations.html

Security

This release contains mitigation for a weakness in the scp(1) tool and protocol (CVE-2019-6111): when copying files from a remote system to a local directory, scp(1) did not verify that the filenames that the server sent matched those requested by the client. This could allow a hostile server to create or clobber unexpected local files with attacker-controlled content.

This release adds client-side checking that the filenames sent from the server match the command-line request. The scp protocol is outdated, inflexible and not readily fixed. We recommend the use of more modern protocols like sftp and rsync for file transfer instead.

Potentially incompatible changes

This release includes a number of changes that may affect existing configurations:

• scp(1): Relating to the above changes to scp(1); the scp protocol relies on the remote shell for wildcard expansion, so there is no infallible way for the client’s wildcard matching to perfectly reflect the server’s. If there is a difference between client and server wildcard expansion, the client may refuse files from the server. For this reason, we have provided a new “-T” flag to scp that disables these client-side checks at the risk of reintroducing the attack described above.
• sshd(8): Remove support for obsolete “host/port” syntax. Slash- separated host/port was added in 2001 as an alternative to host:port syntax for the benefit of IPv6 users. These days there are established standards for this like [::1]:22 and the slash syntax is easily mistaken for CIDR notation, which OpenSSH supports for some things. Remove the slash notation from ListenAddress and PermitOpen; bz#2335

Changes since OpenSSH 7.9

This release is focused on new features and internal refactoring.

New Features

• ssh(1), ssh-agent(1), ssh-add(1): Add support for ECDSA keys in PKCS#11 tokens.
• ssh(1), sshd(8): Add experimental quantum-computing resistant key exchange method, based on a combination of Streamlined NTRU Prime 4591^761 and X25519.
• ssh-keygen(1): Increase the default RSA key size to 3072 bits, following NIST Special Publication 800-57’s guidance for a 128-bit equivalent symmetric security level.
• ssh(1): Allow “PKCS11Provider=none” to override later instances of the PKCS11Provider directive in ssh_config; bz#2974
• sshd(8): Add a log message for situations where a connection is dropped for attempting to run a command but a sshd_config ForceCommand=internal-sftp restriction is in effect; bz#2960
• ssh(1): When prompting whether to record a new host key, accept the key fingerprint as a synonym for “yes”. This allows the user to paste a fingerprint obtained out of band at the prompt and have the client do the comparison for you.
• ssh-keygen(1): When signing multiple certificates on a single command-line invocation, allow automatically incrementing the certificate serial number.
• scp(1), sftp(1): Accept -J option as an alias to ProxyJump on the scp and sftp command-lines.
• ssh-agent(1), ssh-pkcs11-helper(8), ssh-add(1): Accept “-v” command-line flags to increase the verbosity of output; pass verbose flags though to subprocesses, such as ssh-pkcs11-helper started from ssh-agent.
• ssh-add(1): Add a “-T” option to allowing testing whether keys in an agent are usable by performing a signature and a verification.
• sftp-server(8): Add a “[email protected]” protocol extension that replicates the functionality of the existing SSH2_FXP_SETSTAT operation but does not follow symlinks. bz#2067
• sftp(1): Add “-h” flag to chown/chgrp/chmod commands to request they do not follow symlinks.
• sshd(8): Expose $SSH_CONNECTION in the PAM environment. This makes the connection 4-tuple available to PAM modules that wish to use it in decision-making. bz#2741
• sshd(8): Add a ssh_config “Match final” predicate Matches in same pass as “Match canonical” but doesn’t require hostname canonicalisation be enabled. bz#2906
• sftp(1): Support a prefix of ‘@’ to suppress echo of sftp batch commands; bz#2926
• ssh-keygen(1): When printing certificate contents using “ssh-keygen -Lf /path/certificate”, include the algorithm that the CA used to sign the cert.

Bug fixes

• sshd(8): Fix authentication failures when sshd_config contains “AuthenticationMethods any” inside a Match block that overrides a more restrictive default.
• sshd(8): Avoid sending duplicate keepalives when ClientAliveCount is enabled.
• sshd(8): Fix two race conditions related to SIGHUP daemon restart. Remnant file descriptors in recently-forked child processes could block the parent sshd’s attempt to listen(2) to the configured addresses. Also, the restarting parent sshd could exit before any child processes that were awaiting their re-execution state had completed reading it, leaving them in a fallback path.
• ssh(1): Fix stdout potentially being redirected to /dev/null when ProxyCommand=- was in use.
• sshd(8): Avoid sending SIGPIPE to child processes if they attempt to write to stderr after their parent processes have exited; bz#2071
• ssh(1): Fix bad interaction between the ssh_config ConnectTimeout and ConnectionAttempts directives – connection attempts after the first were ignoring the requested timeout; bz#2918
• ssh-keyscan(1): Return a non-zero exit status if no keys were found; bz#2903
• scp(1): Sanitize scp filenames to allow UTF-8 characters without terminal control sequences; bz#2434
• sshd(8): Fix confusion between ClientAliveInterval and time-based RekeyLimit that could cause connections to be incorrectly closed. bz#2757
• ssh(1), ssh-add(1): Correct some bugs in PKCS#11 token PIN handling at initial token login. The attempt to read the PIN could be skipped in some cases, particularly on devices with integrated PIN readers. This would lead to an inability to retrieve keys from these tokens. bz#2652
• ssh(1), ssh-add(1): Support keys on PKCS#11 tokens that set the CKA_ALWAYS_AUTHENTICATE flag by requring a fresh login after the C_SignInit operation. bz#2638
• ssh(1): Improve documentation for ProxyJump/-J, clarifying that local configuration does not apply to jump hosts.
• ssh-keygen(1): Clarify manual – ssh-keygen -e only writes public keys, not private.
• ssh(1), sshd(8): be more strict in processing protocol banners, allowing \r characters only immediately before \n.
• Various: fix a number of memory leaks, including bz#2942 and bz#2938
• scp(1), sftp(1): fix calculation of initial bandwidth limits. Account for bytes written before the timer starts and adjust the schedule on which recalculations are performed. Avoids an initial burst of traffic and yields more accurate bandwidth limits; bz#2927
• sshd(8): Only consider the ext-info-c extension during the initial key eschange. It shouldn’t be sent in subsequent ones, but if it is present we should ignore it. This prevents sshd from sending a SSH_MSG_EXT_INFO for REKEX for buggy these clients. bz#2929
• ssh-keygen(1): Clarify manual that ssh-keygen -F (find host in authorized_keys) and -R (remove host from authorized_keys) options may accept either a bare hostname or a [hostname]:port combo. bz#2935
• ssh(1): Don’t attempt to connect to empty SSH_AUTH_SOCK; bz#2936
• sshd(8): Silence error messages when sshd fails to load some of the default host keys. Failure to load an explicitly-configured hostkey is still an error, and failure to load any host key is still fatal. pr/103
• ssh(1): Redirect stderr of ProxyCommands to /dev/null when ssh is started with ControlPersist; prevents random ProxyCommand output from interfering with session output.
• ssh(1): The ssh client was keeping a redundant ssh-agent socket (leftover from authentication) around for the life of the connection; bz#2912
• sshd(8): Fix bug in HostbasedAcceptedKeyTypes and PubkeyAcceptedKeyTypes options. If only RSA-SHA2 signature types were specified, then authentication would always fail for RSA keys as the monitor checks only the base key (not the signature algorithm) type against *AcceptedKeyTypes. bz#2746
• ssh(1): Request correct signature types from ssh-agent when certificate keys and RSA-SHA2 signatures are in use.

portability

• sshd(8): On Cygwin, run as SYSTEM where possible, using S4U for token creation if it supports MsV1_0 S4U Logon.
• sshd(8): On Cygwin, use custom user/group matching code that respects the OS’ behavior of case-insensitive matching.
• sshd(8): Don’t set $MAIL if UsePAM=yes as PAM typically specifies the user environment if it’s enabled; bz#2937
• sshd(8) Cygwin: Change service name to cygsshd to avoid collision with Microsoft’s OpenSSH port.
• Allow building against OpenSSL -dev (3.x)
• Fix a number of build problems against version configurations and versions of OpenSSL. Including bz#2931 and bz#2921
• Improve warnings in cygwin service setup. bz#2922
• Remove hardcoded service name in cygwin setup. bz#2922