A new version of OpenSSH has been released.
OpenSSH 8.4 has just been released. It will be available from the mirrors listed at https://www.openssh.com/ shortly. 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: https://www.openssh.com/donations.html Future deprecation notice ========================= It is now possible[1] to perform chosen-prefix attacks against the SHA-1 algorithm for less than USD$50K. For this reason, we will be disabling the "ssh-rsa" public key signature algorithm by default in a near-future release. This algorithm is unfortunately still used widely despite the existence of better alternatives, being the only remaining public key signature algorithm specified by the original SSH RFCs. The better alternatives include: * The RFC8332 RSA SHA-2 signature algorithms rsa-sha2-256/512. These algorithms have the advantage of using the same key type as "ssh-rsa" but use the safe SHA-2 hash algorithms. These have been supported since OpenSSH 7.2 and are already used by default if the client and server support them. * The ssh-ed25519 signature algorithm. It has been supported in OpenSSH since release 6.5. * The RFC5656 ECDSA algorithms: ecdsa-sha2-nistp256/384/521. These have been supported by OpenSSH since release 5.7. To check whether a server is using the weak ssh-rsa public key algorithm, for host authentication, try to connect to it after removing the ssh-rsa algorithm from ssh(1)'s allowed list: ssh -oHostKeyAlgorithms=-ssh-rsa user at host If the host key verification fails and no other supported host key types are available, the server software on that host should be upgraded. We intend to enable UpdateHostKeys by default in the next OpenSSH release. This will assist the client by automatically migrating to better algorithms. Users may consider enabling this option manually. [1] "SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust" Leurent, G and Peyrin, T (2020) https://eprint.iacr.org/2020/014.pdf Security ======== * ssh-agent(1): restrict ssh-agent from signing web challenges for FIDO/U2F keys. When signing messages in ssh-agent using a FIDO key that has an application string that does not start with "ssh:", ensure that the message being signed is one of the forms expected for the SSH protocol (currently public key authentication and sshsig signatures). This prevents ssh-agent forwarding on a host that has FIDO keys attached granting the ability for the remote side to sign challenges for web authentication using those keys too. Note that the converse case of web browsers signing SSH challenges is already precluded because no web RP can have the "ssh:" prefix in the application string that we require. * ssh-keygen(1): Enable FIDO 2.1 credProtect extension when generating a FIDO resident key. The recent FIDO 2.1 Client to Authenticator Protocol introduced a "credProtect" feature to better protect resident keys. We use this option to require a PIN prior to all operations that may retrieve a resident key from a FIDO token. Potentially-incompatible changes ================================ This release includes a number of changes that may affect existing configurations: * For FIDO/U2F support, OpenSSH recommends the use of libfido2 1.5.0 or greater. Older libraries have limited support at the expense of disabling particular features. These include resident keys, PIN- required keys and multiple attached tokens. * ssh-keygen(1): the format of the attestation information optionally recorded when a FIDO key is generated has changed. It now includes the authenticator data needed to validate attestation signatures. * The API between OpenSSH and the FIDO token middleware has changed and the SSH_SK_VERSION_MAJOR version has been incremented as a result. Third-party middleware libraries must support the current API version (7) to work with OpenSSH 8.4. * The portable OpenSSH distribution now requires automake to rebuild the configure script and supporting files. This is not required when simply building portable OpenSSH from a release tar file. Changes since OpenSSH 8.3 ========================= New features ------------ * ssh(1), ssh-keygen(1): support for FIDO keys that require a PIN for each use. These keys may be generated using ssh-keygen using a new "verify-required" option. When a PIN-required key is used, the user will be prompted for a PIN to complete the signature operation. * sshd(8): authorized_keys now supports a new "verify-required" option to require FIDO signatures assert that the token verified that the user was present before making the signature. The FIDO protocol supports multiple methods for user-verification, but currently OpenSSH only supports PIN verification. * sshd(8), ssh-keygen(1): add support for verifying FIDO webauthn signatures. Webauthn is a standard for using FIDO keys in web browsers. These signatures are a slightly different format to plain FIDO signatures and thus require explicit support. * ssh(1): allow some keywords to expand shell-style ${ENV} environment variables. The supported keywords are CertificateFile, ControlPath, IdentityAgent and IdentityFile, plus LocalForward and RemoteForward when used for Unix domain socket paths. bz#3140 * ssh(1), ssh-agent(1): allow some additional control over the use of ssh-askpass via a new $SSH_ASKPASS_REQUIRE environment variable, including forcibly enabling and disabling its use. bz#69 * ssh(1): allow ssh_config(5)'s AddKeysToAgent keyword accept a time limit for keys in addition to its current flag options. Time- limited keys will automatically be removed from ssh-agent after their expiry time has passed. * scp(1), sftp(1): allow the -A flag to explicitly enable agent forwarding in scp and sftp. The default remains to not forward an agent, even when ssh_config enables it. * ssh(1): add a '%k' TOKEN that expands to the effective HostKey of the destination. This allows, e.g., keeping host keys in individual files using "UserKnownHostsFile ~/.ssh/known_hosts.d/%k". bz#1654 * ssh(1): add %-TOKEN, environment variable and tilde expansion to the UserKnownHostsFile directive, allowing the path to be completed by the configuration (e.g. bz#1654) * ssh-keygen(1): allow "ssh-add -d -" to read keys to be deleted from stdin. bz#3180 * sshd(8): improve logging for MaxStartups connection throttling. sshd will now log when it starts and stops throttling and periodically while in this state. bz#3055 Bugfixes -------- * ssh(1), ssh-keygen(1): better support for multiple attached FIDO tokens. In cases where OpenSSH cannot unambiguously determine which token to direct a request to, the user is now required to select a token by touching it. In cases of operations that require a PIN to be verified, this avoids sending the wrong PIN to the wrong token and incrementing the token's PIN failure counter (tokens effectively erase their keys after too many PIN failures). * sshd(8): fix Include before Match in sshd_config; bz#3122 * ssh(1): close stdin/out/error when forking after authentication completes ("ssh -f ...") bz#3137 * ssh(1), sshd(8): limit the amount of channel input data buffered, avoiding peers that advertise large windows but are slow to read from causing high memory consumption. * ssh-agent(1): handle multiple requests sent in a single write() to the agent. * sshd(8): allow sshd_config longer than 256k * sshd(8): avoid spurious "Unable to load host key" message when sshd load a private key but no public counterpart * ssh(1): prefer the default hostkey algorithm list whenever we have a hostkey that matches its best-preference algorithm. * sshd(1): when ordering the hostkey algorithms to request from a server, prefer certificate types if the known_hosts files contain a key marked as a @cert-authority; bz#3157 * ssh(1): perform host key fingerprint comparisons for the "Are you sure you want to continue connecting (yes/no/[fingerprint])?" prompt with case sensitivity. * sshd(8): ensure that address/masklen mismatches in sshd_config yield fatal errors at daemon start time rather than later when they are evaluated. * ssh-keygen(1): ensure that certificate extensions are lexically sorted. Previously if the user specified a custom extension then the everything would be in order except the custom ones. bz#3198 * ssh(1): also compare username when checking for JumpHost loops. bz#3057 * ssh-keygen(1): preserve group/world read permission on known_hosts files across runs of "ssh-keygen -Rf /path". The old behaviour was to remove all rights for group/other. bz#3146 * ssh-keygen(1): Mention the [-a rounds] flag in the ssh-keygen manual page and usage(). * sshd(8): explicitly construct path to ~/.ssh/rc rather than relying on it being relative to the current directory, so that it can still be found if the shell startup changes its directory. bz#3185 * sshd(8): when redirecting sshd's log output to a file, undo this redirection after the session child process is forked(). Fixes missing log messages when using this feature under some circumstances. * sshd(8): start ClientAliveInterval bookkeeping before first pass through select() loop; fixed theoretical case where busy sshd may ignore timeouts from client. * ssh(1): only reset the ServerAliveInterval check when we receive traffic from the server and ignore traffic from a port forwarding client, preventing a client from keeping a connection alive when it should be terminated. bz#2265 * ssh-keygen(1): avoid spurious error message when ssh-keygen creates files outside ~/.ssh * sftp-client(1): fix off-by-one error that caused sftp downloads to make one more concurrent request that desired. This prevented using sftp(1) in unpipelined request/response mode, which is useful when debugging. bz#3054 * ssh(1), sshd(8): handle EINTR in waitfd() and timeout_connect() helpers. bz#3071 * ssh(1), ssh-keygen(1): defer creation of ~/.ssh until we attempt to write to it so we don't leave an empty .ssh directory when it's not needed. bz#3156 * ssh(1), sshd(8): fix multiplier when parsing time specifications when handling seconds after other units. bz#3171 Portability ----------- * sshd(8): always send any PAM account messages. If the PAM account stack returns any messages, always send them to the user and not just if the check succeeds. bz#2049 * Implement some backwards compatibility for libfido2 libraries older than 1.5.0. Note that use of an older library will result in the loss of certain features including resident key support, PIN support and support for multiple attached tokens. * configure fixes for XCode 12 * gnome-ssh-askpass3: ensure the "close" button is not focused by default for SSH_ASKPASS_PROMPT=none prompts. Avoids space/enter accidentally dismissing FIDO touch notifications. * gnome-ssh-askpass3: allow some control over textarea colour via $GNOME_SSH_ASKPASS_FG_COLOR and $GNOME_SSH_ASKPASS_BG_COLOR environment variables. * sshd(8): document another PAM spec problem in a frustrated comment * sshd(8): support NetBSD's utmpx.ut_ss address field. bz#960 * Add the ssh-sk-helper binary and its manpage to the RPM spec file * Detect the Frankenstein monster of Linux/X32 and allow the sandbox to function there. bz#3085 Checksums: ========== - SHA1 (openssh-8.4.tar.gz) = 71675139df6807f396e6bd92ff8cb9b0356385d8 - SHA256 (openssh-8.4.tar.gz) = JhBgLYkyRge/zQK8ylBSRcOYvrV/tHwQcvVXfExGB70= - SHA1 (openssh-8.4p1.tar.gz) = 69305059e10a60693ebe6f17731f962c9577535c - SHA256 (openssh-8.4p1.tar.gz) = WgHSLkB+scBbqKj3xlTTiKE+nyJuTtM704dI2vodKyQ= Please note that the SHA256 signatures are base64 encoded and not hexadecimal (which is the default for most checksum tools). The PGP key used to sign the releases is available as RELEASE_KEY.asc from the mirror sites. Reporting Bugs: =============== - Please read https://www.openssh.com/report.html Security bugs should be reported directly to openssh at openssh.com
