===========================================================
== Subject:     Authorization bypass in pki_verify_data_signature
==
== CVE ID#:     CVE-2023-2283
==
== Versions:    (0.9.0 - 0.9.6) and (0.10.0 - 0.10.4)
==
== Summary:     The pki_verify_data_signature can accept invalid
==              signatures when some memory allocations fail.
==
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===========
Description
===========
The authentication check of the connecting client can be bypassed
in the function `pki_verify_data_signature` in circumstances of
memory allocation problems. This may happen f.e. if not enough memory or
the memory usage is limited.

The problem is caused by the return value `rc`, which is initialized to
SSH_ERROR and later rewritten to save the return value of the function
call `pki_key_check_hash_compatible`. The value of the variable is not
changed between this point and the cryptographic verification, therefore
any error between them calls `goto error` returning SSH_OK.

Ed25519 key support is not affected in versions 0.9.x as it is using a
different code path, but the versions 0.10.x are affected. Only OpenSSL
cryptographic backend is affected.

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

Patches addressing the issues have been posted to:
https://www.libssh.org/security/
Additionally, libssh 0.9.7 and 0.10.5 have been issued
as security releases to correct the defect.  SSH administrators are
advised to upgrade to these releases or apply the patch as soon
as possible.

==================
CVSSv3 calculation
==================
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N (4.2)

==========
Workaround
==========
Use Libgcrypt or MbedTLS cryptographic backend.

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

Originally reported by Kevin Backhouse (https://github.com/kevinbackhouse)
from GitHub Security Lab.
Patches provided by Pocs Norbert of the libssh team.

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== The libssh team
==========================================================