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Message-ID: <43950a0c-60c3-479d-a18a-30238bda901e@gmail.com>
Date: Fri, 3 Apr 2026 12:37:29 -0400
From: Demi Marie Obenour <demiobenour@...il.com>
To: oss-security@...ts.openwall.com, Damien Miller <djm@....openbsd.org>
Subject: Re: Announce: OpenSSH 10.3 released
On 4/2/26 05:25, Damien Miller wrote:
> OpenSSH 10.3 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
>
> Potentially-incompatible changes
> --------------------------------
>
> * ssh(1), sshd(8): remove bug compatibility for implementations
> that don't support rekeying. If such an implementation tries to
> interoperate with OpenSSH, it will now eventually fail when the
> transport needs rekeying.
>
> * sshd(8): prior to this release, a certificate that had an empty
> principals section would be treated as matching any principal
> (i.e. as a wildcard) when used via authorized_keys principals=""
> option. This was intentional, but created a surprising and
> potentially risky situation if a CA accidentally issued a
> certificate with an empty principals section: instead of being
> useless as one might expect, it could be used to authenticate as
> any user who trusted the CA via authorized_keys. [Note that this
> condition did not apply to CAs trusted via the sshd_config(5)
> TrustedUserCAKeys option.]
>
> This release treats an empty principals section as never matching
> any principal, and also fixes interpretation of wildcard
> characters in certificate principals. Now they are consistently
> implemented for host certificates and not supported for user
> certificates.
>
> * ssh(1): the -J and equivalent -oProxyJump="..." options now
> validate user and host names for ProxyJump/-J options passed
> via the command-line (no such validation is performed for this
> option in configuration files). This prevents shell injection in
> situations where these were directly exposed to adversarial
> input, which would have been a terrible idea to begin with.
> Reported by rabbit.
>
> Changes since OpenSSH 10.2
> ==========================
>
> This release contains some relatively minor security fixes as well
> as a number of feature improvements and general bugfixes.
>
> Security
> ========
>
> * ssh(1): validation of shell metacharacters in user names supplied
> on the command-line was performed too late to prevent some
> situations where they could be expanded from %-tokens in
> ssh_config. For certain configurations, such as those that use a
> "%u" token in a "Match exec" block, an attacker who can control
> the user name passed to ssh(1) could potentially execute arbitrary
> shell commands. Reported by Florian Kohnhäuser.
>
> We continue to recommend against directly exposing ssh(1) and
> other tools' command-lines to untrusted input. Mitigations such
> as this can not be absolute given the variety of shells and user
> configurations in use.
Is it safe (from a shell injection perspective) to pass inputs that are
sanitized for character set, but otherwise untrusted? For instance,
is it sufficient to limit usernames to ^[A-Za-z][A-Za-z0-9_-]{0,31}$
and domain names to valid host names [1]?
Can one assume that in situations where entries come from an
untrusted source (such as AuthorizedKeysCommand), OpenSSH _does_
do such checking?
[1]: No more than 254 bytes (plus optional trailing '.'), no leading '.',
each '.'-delimited component must start and end with [a-z0-9], not
be more than 63 bytes, and only have [a-z0-9-].
--
Sincerely,
Demi Marie Obenour (she/her/hers)
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