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                        OpenBSD Security Advisory

                            February 8, 2001

             Authentication By-Pass Vulnerability in OpenSSH-2.3.1

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SYNOPSIS

OpenSSH-2.3.1, a development snapshot, only checked if a public key
for public key authentication was permitted.  In the protocol 2 part
of the server, the challenge-response step that ensures that the
connecting client is in possession of the corresponding private key
has been omitted. As a result, anyone who could obtain the public key
listed in the users authorized_keys file could log in as that user
without authentication.

A fix for this problem was committed on Februrary 8th.  The problem
was introduced on January 18th.  This is a three week time window.

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AFFECTED SYSTEMS

This vulnerability affects only OpenSSH version 2.3.1 with support for
protocol 2 enabled.  The latest official release OpenSSH 2.3.0 is not
affected by this problem.  The latest snapshot version OpenSSH 2.3.2
is not affected either.

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RESOLUTION

If you installed the OpenSSH 2.3.1 development snapshot, install the
latest snapshot.  Currently, the latest snapshot is OpenSSH 2.3.2 which
is available via  http://www.openssh.com/.

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