OpenBSD Journal

OpenSSH 5.4 released

Contributed by weerd on from the hush-hush dept.

Damien Miller (djm@) posted to announce@ with the announcement of OpenSSH 5.4. Some highlights of this release are the disabling of protocol 1 by default, certificate authentication, a new 'netcat mode', many changes on the sftp front (both client and server) and a collection of assorted bugfixes. The new release can already be found on a large number of mirrors and of course on

Please read on for the full release announcement:

OpenSSH 5.4 has just been released. It will be available from the
mirrors listed at shortly.

OpenSSH is a 100% complete SSH protocol version 1.3, 1.5 and 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:

This is a major feature and bugfix release.

Changes since OpenSSH 5.3


 * After a transition period of about 10 years, this release disables
   SSH protocol 1 by default. Clients and servers that need to use the
   legacy protocol must explicitly enable it in ssh_config / sshd_config
   or on the command-line.

 * Remove the libsectok/OpenSC-based smartcard code and add support for
   PKCS#11 tokens. This support is automatically enabled on all
   platforms that support dlopen(3) and was inspired by patches written
   by Alon Bar-Lev. Details in the ssh(1) and ssh-add(1) manpages.

 * Add support for certificate authentication of users and hosts using a
   new, minimal OpenSSH certificate format (not X.509). Certificates
   contain a public key, identity information and some validity
   constraints and are signed with a standard SSH public key using
   ssh-keygen(1). CA keys may be marked as trusted in authorized_keys
   or via a TrustedUserCAKeys option in sshd_config(5) (for user
   authentication), or in known_hosts (for host authentication).

   Documentation for certificate support may be found in ssh-keygen(1),
   sshd(8) and ssh(1) and a description of the protocol extensions in

 * Added a 'netcat mode' to ssh(1): "ssh -W host:port ..." This connects
   stdio on the client to a single port forward on the server. This
   allows, for example, using ssh as a ProxyCommand to route connections
   via intermediate servers. bz#1618

 * Add the ability to revoke keys in sshd(8) and ssh(1). User keys may
   be revoked using a new sshd_config(5) option "RevokedKeys". Host keys
   are revoked through known_hosts (details in the sshd(8) man page).
   Revoked keys cannot be used for user or host authentication and will
   trigger a warning if used.

 * Rewrite the ssh(1) multiplexing support to support non-blocking
   operation of the mux master, improve the resilience of the master to
   malformed messages sent to it by the slave and add support for
   requesting port- forwardings via the multiplex protocol. The new
   stdio-to-local forward mode ("ssh -W host:port ...") is also
   supported. The revised multiplexing protocol is documented in the
   file PROTOCOL.mux in the source distribution.

 * Add a 'read-only' mode to sftp-server(8) that disables open in write
   mode and all other fs-modifying protocol methods. bz#430

 * Allow setting an explicit umask on the sftp-server(8) commandline to
   override whatever default the user has. bz#1229

 * Many improvements to the sftp(1) client, many of which were
   implemented by Carlos Silva through the Google Summer of Code
   - Support the "-h" (human-readable units) flag for ls
   - Implement tab-completion of commands, local and remote filenames
   - Support most of scp(1)'s commandline arguments in sftp(1), as a
     first step towards making sftp(1) a drop-in replacement for scp(1).
     Note that the rarely-used "-P sftp_server_path" option has been
     moved to "-D sftp_server_path" to make way for "-P port" to match
   - Add recursive transfer support for get/put and on the commandline

 * New RSA keys will be generated with a public exponent of RSA_F4 ==
   (2**16)+1 == 65537 instead of the previous value 35.

 * Passphrase-protected SSH protocol 2 private keys are now protected
   with AES-128 instead of 3DES. This applied to newly-generated keys
   as well as keys that are reencrypted (e.g. by changing their


 * Hold authentication debug messages until after successful
   authentication. Fixes a minor information leak of environment
   variables specified in authorized_keys if an attacker happens to
   know the public key in use.
 * When using ChrootDirectory, make sure we test for the existence of
   the user's shell inside the chroot and not outside (bz#1679)
 * Cache user and group name lookups in sftp-server using
   user_from_[ug]id(3) to improve performance on hosts where these
   operations are slow (e.g. NIS or LDAP). bz#1495
 * Fix problem that prevented passphrase reading from being interrupted
   in some circumstances; bz#1590
 * Ignore and log any Protocol 1 keys where the claimed size is not
   equal to the actual size.
 * Make HostBased authentication work with a ProxyCommand. bz#1569
 * Avoid run-time failures when specifying hostkeys via a relative
   path by prepending the current working directory in these cases.
 * Do not prompt for a passphrase if we fail to open a keyfile, and log
   the reason why the open failed to debug. bz#1693
 * Document that the PubkeyAuthentication directive is allowed in a
   sshd_config(5) Match block. bz#1577
 * When converting keys, truncate key comments at 72 chars as per
   RFC4716. bz#1630
 * Do not allow logins if /etc/nologin exists but is not readable by the
   user logging in.
 * Output a debug log if sshd(8) can't open an existing authorized_keys.
 * Quell tc[gs]etattr warnings when forcing a tty (ssh -tt), since we
   usually don't actually have a tty to read/set; bz#1686
 * Prevent sftp from crashing when given a "-" without a command.
   Also, allow whitespace to follow a "-". bz#1691
 * After sshd receives a SIGHUP, ignore subsequent HUPs while sshd
   re-execs itself. Prevents two HUPs in quick succession from resulting
   in sshd dying. bz#1692
 * Clarify in sshd_config(5) that StrictModes does not apply to
   ChrootDirectory. Permissions and ownership are always checked when
   chrooting. bz#1532
 * Set close-on-exec on various descriptors so they don't get leaked to
   child processes. bz#1643
 * Fix very rare race condition in x11/agent channel allocation: don't
   read after the end of the select read/write fdset and make sure a
   reused FD is not touched before the pre-handlers are called.
 * Fix incorrect exit status when multiplexing and channel ID 0 is
   recycled. bz#1570
 * Fail with an error when an attempt is made to connect to a server
   with ForceCommand=internal-sftp with a shell session (i.e. not a
   subsystem session). Avoids stuck client when attempting to ssh to
   such a service. bz#1606:
 * Warn but do not fail if stat()ing the subsystem binary fails. This
   helps with chrootdirectory+forcecommand=sftp-server and restricted
   shells. bz #1599
 * Change "Connecting to host..." message to "Connected to host."
   and delay it until after the sftp protocol connection has been
   established. Avoids confusing sequence of messages when the
   underlying ssh connection experiences problems. bz#1588
 * Use the HostKeyAlias rather than the hostname specified on the
   commandline when prompting for passwords. bz#1039
 * Correct off-by-one in percent_expand(): we would fatal() when trying
   to expand EXPAND_MAX_KEYS, allowing only EXPAND_MAX_KEYS-1 to
   actually work. Note that nothing in OpenSSH actually uses close to
   this limit at present. bz#1607
 * Fix passing of empty options from scp(1) and sftp(1) to the
   underlying ssh(1). Also add support for the stop option "--".
 * Fix an incorrect magic number and typo in PROTOCOL; bz#1688
 * Don't escape backslashes when displaying the SSH2 banner. bz#1533
 * Don't unnecessarily dup() the in and out fds for sftp-server. bz#1566
 * Force use of the correct hash function for random-art signature

Thanks to all the OpenSSH developers for this new release. Now is the time for you to go and upgrade your ssh installations to 5.4!

(Comments are closed)

  1. By Chris (LizardKing) on

    From the changes to the sftp client:

    Implement tab-completion of commands, local and remote filenames

    Many thanks for this - I often find myself hitting tab in sftp sessions expecting command line completion!


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