===========================================================
== Subject:     Missing principal-to-user check in gssapi-keyex
==
== CVE ID#:     CVE-2026-59851
==
== Versions:    libssh 0.12.0
==
== Summary:     A client with valid Kerberos credentials can
==              impersonate any user on a libssh server with
==              enabled GSSAPIKeyExchange.
==
== Component:   server
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===========
Description
===========

The libssh server implementation did not dispatch any
authorization callback when handling the gssapi-keyex
authentication request. SSH servers built on libssh
which enable GSSAPIKeyExchange therefore did not have
means to check that an authenticated client (with
a valid Kerberos ticket for some principal) is authorized
to log in under the requested username. As a result,
any client with valid Kerberos credentials would be
able to log in as an arbitrary local user.

Note that SSH server implementations built on libssh
are still expected to provide the callback themselves,
as there are multiple ways to implement the authorization.

==================
Patch Availability
==================

Patches addressing the issues have been posted to:
https://www.libssh.org/security/
Additionally, libssh 0.12.1 has been issued
as a security release to correct the defect.  SSH administrators are
advised to upgrade to this release or apply the patch as soon
as possible.

==================
CVSSv3 calculation
==================
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (8.8)

==========
Workaround
==========

Disable GSSAPIKeyExchange.

=======
Credits
=======

Reported by Aisle Research in partnership with Red Hat,
patch provided by Pavol Zacik of the libssh team.

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== The libssh team
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