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AUSCERT External Security Bulletin Redistribution
ESB-2002.348 -- FreeBSD-SA-02:31.openssh
openssh contains remote vulnerability
16 July 2002
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AusCERT Security Bulletin Summary
---------------------------------
Product: openssh
Vendor: FreeBSD
Operating System: FreeBSD-CURRENT (see dates in advisory)
Impact: Root Compromise
Access Required: Remote
Comments: Note that according to the included advisory, this issue
affects FreeBSD-CURRENT only.
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FreeBSD-SA-02:31 Security Advisory
The FreeBSD Project
Topic: openssh contains remote vulnerability
Category: core
Module: OpenSSH
Announced: 2002-07-15
Credits: ISS X-Force <xforce@ISS.net>
Theo DeRaadt <deraadt@OpenBSD.org>
Affects: FreeBSD-CURRENT between 2002-03-18 and 2002-06-25
Corrected: 2002-06-25 19:10:07 (HEAD)
FreeBSD only: NO
I. Background
OpenSSH is a free implementation of the SSH protocol suite, and
provides encrypted and authenticated remote login, file transfer and
command execution.
II. Problem Description
SSH clients and servers communicate by exchanging discrete messages
with a variable number of parameters. Due to the lack of sufficient
integrity checks in a portion of the server code responsible for
handling incoming SSH2_MSG_USERAUTH_INFO_RESPONSE messages, it was
possible for a malicious client to send a message that would cause the
server to overwrite portions of its memory with client-provided data.
III. Impact
An remote attacker using an SSH client modified to send carefully
crafted SSH2_MSG_USERAUTH_INFO_RESPONSE to the server could obtain
superuser privileges on the server.
Please note that this problem only affects FreeBSD-CURRENT. No
versions of FreeBSD-STABLE are or were ever vulnerable to this bug.
IV. Workaround
Do one of the following:
1) Disable SSH entirely.
2) Use a firewall to block incoming SSH connections from untrusted
hosts.
3) Add the following line to /etc/ssh/sshd_config, and restart sshd.
ChallengeResponseAuthentication no
Note that this will prevent the use of OPIE and similar challenge-
based authentication methods with SSH.
V. Solution
Update your system to the latest -CURRENT.
VI. Correction details
No correction details are provided in this advisory.
VII. References
<URL:http://www.openssh.com/txt/preauth.adv>
<URL:http://www.iss.net/security_center/static/9169.php>
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