Call for testing: OpenSSH 10.0

[Darren Tucker]

Hi all.

OpenSSH 10.0p1 is almost ready for release, so we would appreciate testing
on as many platforms and systems as possible. This is primarily a bugfix
release, although one notable change is the introduction of the sshd-auth
binary (see below).

Snapshot releases for portable OpenSSH are available from
http://www.mindrot.org/openssh_snap/

The OpenBSD version is available in CVS HEAD:
http://www.openbsd.org/anoncvs.html

Portable OpenSSH is also available via git using the
instructions at http://www.openssh.com/portable.html#cvs
At https://anongit.mindrot.org/openssh.git/ or via a mirror at Github:
https://github.com/openssh/openssh-portable

Running the regression tests supplied with Portable OpenSSH does not
require installation and is a simply:

$ ./configure && make tests

Live testing on suitable non-production systems is also appreciated.
Please send reports of success or failure to
openssh-unix-dev at mindrot.org. Security bugs should be reported
directly to openssh at openssh.com.

Below is a summary of changes. More detail may be found in the ChangeLog
in the portable OpenSSH tarballs.

Thanks to the many people who contributed to this release.

Potentially-incompatible changes
--------------------------------

 * This release removes support for the weak DSA signature
   algorithm, completing the deprecation process that began in
   2015 (when DSA was disabled by default) and repeatedly warned
   over the the last 12 months.

 * This release has the version number 10.0 and announces itself
   as "SSH-2.0-OpenSSH_10.0". Software that naively matches
   versions using patterns like "OpenSSH_1*" may be confused by
   this.

 * sshd(8): this release removes the code responsible for the
   user authentication phase of the protocol from the per-
   connection sshd-session binary to a new sshd-auth binary.
   Splitting this code into a separate binary ensures that the
   crucial pre-authentication attack surface has an entirely
   disjoint address space from the code used for the rest of the
   connection. It also yields a small runtime memory saving as the
   authentication code will be unloaded after the authentication
   phase completes. This change should be largely invisible to
   users, though some log messages may now come from "sshd-auth"
   instead of "sshd-session". Downstream distributors of OpenSSH
   will need to package the sshd-auth binary.

 * sshd(8): this release disables finite field (a.k.a modp)
   Diffie-Hellman key exchange in sshd by default. Specifically,
   this removes the "diffie-hellman-group*" and
   "diffie-hellman-group-exchange-*" methods from the default
   KEXAlgorithms list. The client is unchanged and continues to
   support these methods by default. Finite field Diffie Hellman
   is slow and computationally expensive for the same security
   level as Elliptic Curve DH or PQ key agreement while offering
   no redeeming advantages. ECDH has been specified for the SSH
   protocol for 15 years and some form of ECDH has been the default
   key exchange in OpenSSH for the last 14 years.

 * sshd(8): this release removes the implicit fallback to compiled-
   in groups for Diffie-Hellman Group Exchange KEX when the moduli
   file exists but does not contain moduli within the client-
   requested range.  The fallback behaviour remains for the case
   where the moduli file does not exist at all. This allows
   administrators more explicit control over which DH groups will
   be selected, but can lead to connection failures if the moduli
   file is edited incorrectly. bz#2793

 * sftp(1) and scp(1) will now explicitly not create a ControlMaster mux
   connection, since doing so would potentially create one with
   options more restrictive than those specified in the config file.
   This could lead to later confusion, particularly when used with
   ControlMaster=auto.  sftp(1) and scp(1) can still use a mux connection,
   so ssh(1) can be used to establish one, after which they can use it
   as per usual.

Changes since OpenSSH 9.9
=========================

New features
------------

 * ssh(1): the hybrid post-quantum algorithm mlkem768x25519-sha256
   is now used by default for key agreement. This algorithm is
   considered to be safe against attack by quantum computers,
   is guaranteed to be no less strong than the popular
   curve25519-sha256 algorithm, has been standardised by NIST
   and is considerably faster than the previous default.

 * ssh(1): prefer AES-GCM to AES-CTR mode when selecting a cipher
   for the connection. The default cipher preference list is now
   Chacha20/Poly1305, AES-GCM (128/256) followed by AES-CTR
   (128/192/256).

 * ssh(1): add %-token and environment variable expansion to the
   ssh_config SetEnv directive.

 * ssh(1): allow %-token and environment variable expansion in
   the ssh_config User directive, with the exception of %r and %C
   which would be self-referential. bz#3477

 * ssh(1), sshd(8): add "Match version" support to ssh_config and
   sshd_config. Allows matching on the local version of OpenSSH,
   e.g. "Match version OpenSSH_10.*".

 * ssh(1): add support for "Match sessiontype" to ssh_config.
   Allows matching on the type of session initially requested,
   either "shell" for interactive sessions, "exec" for command
   execution sessions, "subsystem" for subsystem requests, such as
   sftp, or "none" for transport/forwarding-only sessions.

 * ssh(1): add support for "Match command ..." support to
   ssh_config, allowing matching on the remote command as specified
   on the command-line.

 * ssh(1): allow 'Match tagged ""' and 'Match command ""' to match
   empty tag and command values respectively.

 * sshd(8): allow glob(3) patterns to be used in sshd_config
   AuthorizedKeysFile and AuthorizedPrincipalsFile directives.
   bz2755

 * sshd(1): support the VersionAddendum in the client, mirroring
   the option of the same name in the server; bz2745

 * ssh-agent(1): the agent will now delete all loaded keys when
   signaled with SIGUSR1. This allows deletion of keys without
   having access to $SSH_AUTH_SOCK.

 * Portable OpenSSH, ssh-agent(1): support systemd-style socket
   activation in ssh-agent using the LISTEN_PID/LISTEN_FDS
   mechanism. Activated when these environment variables are set,
   the agent is started with the -d or -D option and no socket path
   is set. GHPR502

 * ssh-keygen(1): support FIDO tokens that return no attestation
   data, e.g. recent WinHello. GHPR542

 * ssh-agent(1): add a "-Owebsafe-allow=..." option to allow the
   default FIDO application ID allow-list to be overridden.

 * Add a work-in-progress tool to verify FIDO attestation blobs
   that ssh-keygen can optionally write when enrolling FIDO keys.
   This tool is available under regress/misc/ssh-verify-attestation
   for experimentation but is not installed by "make install".

 * ssh-keygen(1): allow "-" as output file for moduli screening.
   GHPR393

Bugfixes
--------

 * sshd(8): remove assumption that the sshd_config and any configs
   it includes can fit in a (possibly enlarged) socket buffer.
   Previously it was possible to create a sufficiently large
   configuration that could cause sshd to fail to accept any
   connection. sshd(8) will now actively manage sending its config
   to the sshd-session sub-process.

 * ssh(1): don't start the ObscureKeystrokeTiming mitigations if
   there has been traffic on a X11 forwarding channel recently.
   Should fix X11 forwarding performance problems when this setting
   is enabled. bz3655

 * ssh(1): prohibit the comma character in hostnames accepted, but
   allow an underscore as the first character in a hostname.

 * sftp(1): set high-water when resuming a "put". Prevents bogus
   "server reordered acks" debug message.

 * ssh(1), sshd(8): fix regression in openssh-9.8, which would fail
   to accept "Match criteria=argument" as well as the documented
   "Match criteria argument" syntax in ssh_config and sshd_config.
   bz3739

 * scp(1), sftp(1): pass "ControlMaster no" to ssh when invoked by
   scp & sftp. This disables implicit session creation by these
   tools when ControlMaster was set to yes/auto by configuration,
   which some users found surprising. This change will not prevent
   scp/sftp from using an existing multiplexing session if one had
   already been created. GHPR557

 * sftp(1), ssh(1): fix a number possible NULL dereference bugs,
   including Coverity CIDs 405019 and 477813.

 * sshd(8): fix PerSourcePenalty incorrectly using "crash" penalty
   when LoginGraceTime was exceeded. bz3797

 * sshd(8): fix "Match invalid-user" from incorrectly being
   activated in initial configuration pass when no other predicates
   were present on the match line

 * sshd(8): fix debug logging of user specific delay. GHPR#552

 * sshd(8): improve debug logging across sub-process boundaries.
   Previously some log messages were lost early in the sshd-auth and
   sshd-session processes' life.

 * ssh(1): require control-escape character sequences passed via
   the '-e ^x' command-line to be exactly two characters long. Avoids
   one byte out-of-bounds read if ssh is invoked as "ssh -e^ ..."
   GHPR368

 * ssh(1), sshd(8): prevent integer overflow in x11 port handling.
   These are theoretically possible if the admin misconfigured
   X11DisplayOffset or the user misconfigures their own $DISPLAY,
   but don't happen in normal operation. bz#3730

 * ssh-keygen(1): don't mess up ssh-keygen -l output when the file
   contains CR characters; GHPR236 bz3385.

 * sshd(8): add rate limits to logging of connections dropped by
   PerSourcePenalties. Previously these could be noisy in logs.

 * ssh(1): fix argument of "Compression" directive in ssh -G config
   dump, which regressed in openssh-9.8.

 * sshd(8): fix a corner-case triggered by UpdateHostKeys when sshd
   refuses to accept the signature returned by an agent holding host
   keys during the hostkey rotation sub-protocol. This situation
   could occur in situations where a PKCS#11 smartcard that lacked
   support for particular signature algorithms was used to store
   host keys.

 * ssh-keygen(1): when using RSA keys to sign messages with
   "ssh-keygen -Y", select the signature algorithm based on the
   requested hash algorithm ("-Ohashalg=xxx"). This allows using
   something other than the default of rsa-sha2-512, which may not
   be supported on all signing backends, e.g. some smartcards only
   support SHA256.

 * ssh(1), sshd(8), ssh-keyscan(1): fix ML-KEM768x25519 KEX on
   big-endian systems.

 * Many regression and interop test improvements.

Portability
-----------

 * All: add support for AWS-LC (AWS libcrypto). bz3784

 * sshd(8): add wtmpdb support as a Y2038 safe wtmp replacement.

 * sshd(8): add support for locking sshd into memory, enabled with
   the --with-linux-memlock-onfault configure flag.

 * Add support for building a standalone sk-libfido2 library,
   enabled by --with-security-key-standalone

 * ssh(1), sshd(8), ssh-keyscan(1): include __builtin_popcount
   replacement function. for compilers that lack it.

 * All: Check for and replace le32toh, le64toh, htole64 separately.
   It appears that at least some versions of endian.h in glibc do
   not have the latter two. bz#3794

 * Remove ancient RHL 6.x config in RPM spec.

OpenSSH is brought to you by Markus Friedl, Niels Provos, Theo de
Raadt, Kevin Steves, Damien Miller, Darren Tucker, Jason McIntyre,
Tim Rice and Ben Lindstrom.

-- 
Darren Tucker (dtucker at dtucker.net)
GPG key 11EAA6FA / A86E 3E07 5B19 5880 E860  37F4 9357 ECEF 11EA A6FA
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.