OpenSSH 5.6 released

Valic —  August 30, 2010 — Leave a comment

OpenSSH 5.6 has just been released. It will be available from the mirrors listed at shortly.


* Added a ControlPersist option to ssh_config(5) that automatically starts a background ssh(1) multiplex master when connecting. This connection can stay alive indefinitely, or can be set to automatically close after a user-specified duration of inactivity.

* Hostbased authentication may now use certificate host keys. CA keys must be specified in a known_hosts file using the @cert-authority marker as described in sshd(8).

* ssh-keygen(1) now supports signing certificate using a CA key that has been stored in a PKCS#11 token.

* ssh(1) will now log the hostname and address that we connected to at LogLevel=verbose after authentication is successful to mitigate “phishing” attacks by servers with trusted keys that accept authentication silently and automatically before presenting fake password/passphrase prompts.

Note that, for such an attack to be successful, the user must have disabled StrictHostKeyChecking (enabled by default) or an attacker must have access to a trusted host key for the destination server.

* Expand %h to the hostname in ssh_config Hostname options. While this sounds useless, it is actually handy for working with unqualified


Host *.*
Hostname %h
Host *

* Allow ssh-keygen(1) to import (-i) and export (-e) of PEM and PKCS#8 keys in addition to RFC4716 (SSH.COM) encodings via a new -m option

* sshd(8) will now queue debug messages for bad ownership or permissions on the user’s keyfiles encountered during authentication and will send them after authentication has successfully completed. These messages may be viewed in ssh(1) at LogLevel=debug or higher.

* ssh(1) connection multiplexing now supports remote forwarding with dynamic port allocation and can report the allocated port back to the user:

LPORT=`ssh -S muxsocket -R0:localhost:25 -O forward somehost`

* sshd(8) now supports indirection in matching of principal names listed in certificates. By default, if a certificate has an embedded principals list then the username on the server must match one of the names in the list for it to be accepted for authentication.

sshd(8) now has a new AuthorizedPrincipalsFile option to specify a file containing a list of names that may be accepted in place of the username when authorizing a certificate trusted via the sshd_config(5) TrustedCAKeys option. Similarly, authentication using a CA trusted in ~/.ssh/authorized_keys now accepts a principals=”name1[,name2,…]” to specify a list of permitted names.

If either option is absent, the current behaviour of requiring the username to appear in principals continues to apply. These options are useful for role accounts, disjoint account namespaces and “user at realm“-style naming policies in certificates.

* Additional sshd_config(5) options are now valid inside Match blocks:


* Revised the format of certificate keys. The new format, identified as ssh-{dss,rsa}-cert-v01 at includes the following changes:

– Adding a serial number field. This may be specified by the CA at the time of certificate signing.

– Moving the nonce field to the beginning of the certificate where it can better protect against chosen-prefix attacks on the signature hash (currently infeasible against the SHA1 hash used)

– Renaming the “constraints” field to “critical options”

– Addng a new non-critical “extensions” field. The “permit-*” options are now extensions, rather than critical options to permit non

-OpenSSH implementation of this key format to degrade gracefully when encountering keys with options they do not recognize.

The older format is still supported for authentication and may still be used when signing certificates (use “ssh-keygen -t v00 …”).
The v00 format, introduced in OpenSSH 5.4, will be supported for at least one year from this release, after which it will be deprecated and removed.


* The PKCS#11 code now retries a lookup for a private key if there is no matching key with CKA_SIGN attribute enabled; this fixes fixes MuscleCard support (bz#1736)

* Unbreak strdelim() skipping past quoted strings (bz#1757). For example, the following directive was not parsed correctly:

AllowUsers “blah blah” blah

* sftp(1): fix swapped args in upload_dir_internal(), breaking recursive upload depth checks and causing verbose printing of transfers to always be turned on (bz#1797)

* Fix a longstanding problem where if you suspend scp(1) at the password/passphrase prompt the terminal mode is not restored.

* Fix a PKCS#11 crash on some smartcards by validating the length returned for C_GetAttributValue (bz#1773)

* sftp(1): fix ls in working directories that contain globbing characters in their pathnames (bz#1655)

* Print warning for missing home directory when ChrootDirectory=none (bz#1564)

* sftp(1): fix a memory leak in do_realpath() error path (bz#1771)

* ssk-keygen(1): Standardise error messages when attempting to open private key files to include “progname: filename: error reason” (bz#1783)

* Replace verbose and overflow-prone Linebuf code with read_keyfile_line() (bz#1565)

* Include the user name on “subsystem request for …” log messages

* ssh(1) and sshd(8): remove hardcoded limit of 100 permitopen clauses and port forwards per direction (bz#1327)

* sshd(8): ignore stderr output from subsystems to avoid hangs if a subsystem or shell initialisation writes to stderr (bz#1750)

* Skip the initial check for access with an empty password when PermitEmptyPasswords=no (bz#1638)

* sshd(8): fix logspam when key options (from=”…” especially) deny non-matching keys (bz#1765)

* ssh-keygen(1): display a more helpful error message when $HOME is inaccessible while trying to create .ssh directory (bz#1740)

* ssh(1): fix hang when terminating a mux slave using ~. (bz#1758)

* ssh-keygen(1): refuse to generate keys longer than OPENSSL_[RD]SA_MAX_MODULUS_BITS, since we would refuse to use them anyway (bz#1516)

* Suppress spurious tty warning when using -O and stdin is not a tty (bz#1746)

* Kill channel when pty allocation requests fail. Fixed stuck client if the server refuses pty allocation (bz#1698)

Portable OpenSSH Bugfixes:

* sshd(8): increase the maximum username length for login recording to 512 characters (bz#1579)

* Initialize the values to be returned from PAM to sane values in case the PAM method doesn’t write to them. (bz#1795)

* Let configure find OpenSSL libraries in a lib64 subdirectory. (bz#1756)


– SHA1 (openssh-5.6.tar.gz) = fa5ac394b874d6709031306b6ac5c48399697f7f
– SHA1 (openssh-5.6p1.tar.gz) = 347dd39c91c3529f41dae63714d452fb95efea1e

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