Call for testing: OpenSSH 10.4

Tue Jun 30 12:58:34 AEST 2026

Hi,

OpenSSH 10.4p1 is almost ready for release, so we would appreciate testing
on as many platforms and systems as possible. This is a bugfix release.

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
--------------------------------

 * sshd(8): configuration dump mode ("sshd -G") now writes directives
   in mixed case (e.g. "PubkeyAuthentication") whereas previously it
   emitted only lower-case names.

 * sshd(8): on Linux systems with the seccomp sandbox enabled,
   failures to enable SECCOMP or NO_NEW_PRIVS are now fatal.
   Previously sshd(8) would log the error but continue operation,
   to support systems that lacked these features. Now systems that
   lack these should instead disable the sandbox at configure time.

 * ssh(1), sshd(8): make the transport protocol stricter by
   disconnecting if the peer sends non-KEX messages during a post-
   authentication key re-exchange. Previously a malicious peer could
   continue sending non-key exchange messages without penalty. These
   would be buffered, causing memory to be wasted up until the
   connection terminated or the server/client hit a memory limit.
   Implementations that do not restrict messages sent during key
   exchange as per RFC4253 section 7.1 may be disconnected.
   Reported by Marko Jevtic.

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

 * All: add experimental support for a composite post-quantum
   signature scheme that combines ML-DSA 44 and Ed25519 as specified
   in draft-miller-sshm-mldsa44-ed25519-composite-sigs.

   This scheme is not enabled by default. To use it, you'll need
   to add it to HostKeyAlgorithms, PubkeyAcceptedAlgorithms, etc.
   Keys may be generated using "ssh-keygen -t mldsa44-ed25519".

 * ssh(1), sshd(8): replace the wildcard pattern matcher with an
   implementation based on an NFA. This avoids exponential worst-case
   behaviour for the old implementation.

Bugfixes
--------

 * ssh-agent(1): fix incorrect reply to "query" SSH_AGENTC_EXTENSION
   requests. bz3967

 * ssh(1), sshd(8): fix several bugs that incorrectly
   classified bulk traffic as interactive. bz3972, bz3958

 * ssh-keygen(1), ssh-add(1): skip unsupported key types when
   downloading resident keys from a FIDO token. Previously, downloads
   would abort when one was encountered. GHPR657

 * ssh(1): fix a potential use-after-free on an error path if
   cipher_init() fails.

 * sshd(8): perform stricter encoding and validation of transport
   state passed between sshd privilege separation subprocesses. This
   somewhat further hardens the server against attacks on sshd-auth
   or sshd-session subprocesses.

 * ssh-agent(1): avoid possible runtime denial of service by
   enforcing some limits on the length of usernames in key use
   constraints.

 * sftp(1): fix two separate one-byte out-of-bounds reads, in
   SSH2_FXP_REALPATH and batch command processing.

 * sftp-server(8): disallow use of the copy-data extension to read
   and write to the same inode simultaneously.

 * ssh(1), sshd(8): avoid strlen(NULL) crash if an X11 channel was
   created before the x11-req SSH_MSG_CHANNEL_REQUEST was sent.
   GHPR679

 * sftp(1), scp(1): avoid a situation where sftp_download() could get
   stuck in a loop if a broken server repeatedly returned zero length
   while reading a file.

 * ssh(1): avoid leaking DNS0x20 case-randomised names into names
   canonicalised using CanonicalizePermittedCNAMEs. bz3966

 * sftp-server(8): avoid truncation of pathnames passed to lstat()
   during SSH_FXP_REALPATH handling on systems where PATH_MAX is not
   the actual max. GHPR688

 * ssh(1), sshd(8): correct arming of poll(2) event masks for some
   socket-type channels. GHPR660

 * sshd(8): major refactor of sshd_config parsing and management
   code, to allow for more exact serialisation/deserialisation across
   privilege separation boundaries.

 * ssh-add(1): open connection to the agent only after getopt()
   processing has completed, to give options like "-v" a chance to
   display debug information about this operation.

 * crypto code: fix bounds checking when signing messages of length
   greater than will fit in a size_t. In OpenSSH, message sizes are
   bounded by SSHBUF_SIZE_MAX so this was unreachable.

 * crypto code: add signature malleability and pubkey validity checks
   to ed25519 verification. SSH doesn't depend on these properties

 * crypto code: fix ECDSA order check for curves with cofactor != 1.
   All supported EC curves have cofactor 1, so this was
   unreachable.

 * sshd(8): differentiate between execution failures and a subsystem
   that was not found when logging why a subsystem failed to start.
   GHPR637

 * All: use safer idioms for timegm(3) and mktime(3) error detection.

 * ssh(1), sshd(8): avoid accepting invalid cipher or MAC lists in
   config files or command-line arguments. This could cause runtime
   failures later.

 * ssh(1): fix NULL deref crash during pubkey auth when using a PEM
   style private key with no corresponding .pub key adjacent to it.

 * sshd(8): don't print an error message when trying to load a host
   private key when PKCS#11 keys are in use, as these don't need the
   private half on the filesystem. GHPR664

 * All: don't use deprecated ERR_load_crypto_strings(). GHPR650

 * ssh(1): properly report errors during configuration default
   setting. GHPR649

 * ssh(1): use correct directive name (Match instead of Host) in
   error message. bz3968

 * sftp(1): fix "ls -ln" which was not correctly showing numeric
   UID/GIDs but rather user and group names. bz3953

 * sshd(8): avoid possible NULL dereference if an allocation fails
   during config parsing. bz3948

 * All: fix ineffective guards against loading overly large public
   keys in several places. bz3969 and bz3970

 * sftp(1): ensure file descriptors used by sftp to communicate to
   its ssh(1) subprocess don't leak into executed subprocesses (e.g.
   via "!"). GHPR693

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

 * Sync fmt_scaled.c with OpenBSD upstream, picking up an exactness
   fix for large exponents (GHPR671)

 * sshd(8): remove duplicate sandbox entry for clock_gettime64.

 * ssh(1), sshd(8): use correct IPTOS_DSCP_VA value if not provided
   by the system headers.

 * Sync getrrsetbyname.c with OpenBSD upstream, picking up robustness
   fixes.

 * Disable replacements in openbsd-compat for strvisx(3) and
   stravis(3), as these are unused in OpenSSH

 * Avoid fortify warnings on Android bz3954

 * Fix a number of memory leaks on error paths in the portability
   code. GHPR681

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.