LinuxSecurity.com
Share your story
The central voice for Linux and Open Source security news
Home News Topics Advisories HOWTOs Features Newsletters About Register

Welcome!
Sign up!
EnGarde Community
Login
Polls
What is the most important Linux security technology?
 
Advisories
Community
Linux Events
Linux User Groups
Link to Us
Security Center
Book Reviews
Security Dictionary
Security Tips
SELinux
White Papers
Featured Blogs
All About Linux
DanWalsh LiveJournal
Securitydistro
Latest Newsletters
Linux Security Week: April 21st, 2014
Linux Security Week: April 7th, 2014
Subscribe
LinuxSecurity Newsletters
E-mail:
Choose Lists:
About our Newsletters
RSS Feeds
Get the LinuxSecurity news you want faster with RSS
Powered By

  
NetBSD: 'OpenSSH' Remote Vulnerability Print E-mail
User Rating:      How can I rate this item?
Posted by LinuxSecurity.com Team   
NetBSD OpenSSH has a vulnerability in protocol version 2 challenge-responseauthentication. OpenSSH 3.4 must be installed to completely overcome theproblem.

 NetBSD Security Advisory 2002-005
		 =================================

Topic:		OpenSSH protocol version 2 challenge-response authentication
		vulnerability

Version:	NetBSD-current:	prior to May 14, 2002
		NetBSD-1.6_BETAx: affected
		NetBSD-1.5.2:	affected
		NetBSD-1.5.1:	affected
		NetBSD-1.5:	affected
		NetBSD-1.4.*:	not affected (does not ship with OpenSSH)
		pkgsrc:		packages prior to openssh-3.3.0.1

Severity:	high, remote root compromise

Workaround:	NetBSD-current:		May 14, 2002
		NetBSD-1.6 branch:	partial by default (priv sep)
		NetBSD-1.5 branch:	instructions below, OpenSSH 3 and later
		pkgsrc:			June 25, 2002 (with openssh-3.3.0.1)

Fixed:		NetBSD-current:		June 26, 2002 (OpenSSH 3.4)
		NetBSD-1.6 branch:	June 26, 2002 (OpenSSH 3.4)
		NetBSD-1.5 branch:	June 26, 2002 (patch on advisory)
		pkgsrc:			June 26, 2002 (with openssh-3.4.0.1)

		Version string "NetBSD_Secure_Shell-20020626" will identify
		that the fix is in place.


Abstract
========

OpenSSH has a vulnerability in protocol version 2 challenge-response
authentication.  OpenSSH 3.4 must be installed to completely overcome the
problem.

Technical Details
=================

Vulnerability itself: 
http://bvlive01.iss.net/issEn/delivery/xforce/alertdetail.jsp?oid=20584 
http://openssh.org/txt/iss.adv 
http://openssh.org/txt/preauth.adv

CERT CA-2002-18 
http://www.cert.org/advisories/CA-2002-18.html 
http://www.kb.cert.org/vuls/id/369347


Solutions and Workarounds
=========================

Some workarounds are available, which may somewhat mitigate the risk:

 - Turn off challenge-response authentication by having the following
   in sshd_config:
	ChallengeResponseAuthentication no

   On some systems, the following option is also required together
   with the above. It is not relevant for NetBSD.
	PAMAuthenticationViaKbdInt no

   Note that turning these features off will disable SSH logins via
   S/Key (OTP) authentication.  Compiling OpenSSH without support for
   S/Key and PAM authentication will also eliminate this
   vulnerability.

 - If you do not require SSH Protocol version 2 support, disabling it
   will eliminate the vulnerable codepath. Remember that version 1 is
   considered significantly less secure than version 2, and this
   workaround is not recommended for long term use. Additionally, if
   your users use version 2 authentication methods, they will be unable
   to connect.

 - The new Privelege Separation feature (available since OpenSSH
   3.2.x) has been promoted as a potential mitigation of this issue.
   This feature is available in NetBSD-current as of May 14th, and is
   enabled by default.

   Privilege Separation might provide a benefit, potentially
   preventing this or future vulnerabilities from being root exploits,
   and limiting their nature to a denial of service.  Although a
   useful defensive feature, this is not guaranteed, expecially given
   the implementation has not yet met the test of time.

   Do not avoid patching this issue simply because you have enabled
   Privelege Separation.

   Effect of privilege separation:
      http://www.citi.umich.edu/u/provos/ssh/privsep.html


The following instructions describe how to upgrade your OpenSSH
binaries by updating your source tree and rebuilding and
installing a new version.

Releases of NetBSD 1.5.3 and NetBSD 1.6 are imminent. This is a reminder
to consider upgrading when they are available, if you are running
anything older than NetBSD 1.5.3.  Many security-related improvements
have been made.

To check if your system has a vulnerable version of sshd, run "sshd -V"
(it is an invalid argument, but it will present the version number).
Any version dated "NetBSD_Secure_Shell-20020626" or later will identify
that the fix is in place.

Although workarounds were provided above, update your binaries to make
very sure that you don't have vulnerable binaries around.


* NetBSD-current:

	Systems running NetBSD-current dated from before 2002-05-13
	should be upgraded to NetBSD-current dated 2002-05-14 or later
	if you wish to use privilege separation support as a stopgap measure.
	It is recommended to update to source dated 2002-06-26 for a
	complete fix (with OpenSSH 3.4).

	The following directories need to be updated from the
	netbsd-current CVS branch (aka HEAD):
		crypto/dist/ssh
		usr.bin/ssh

	To update from CVS, re-build, and re-install:
		# cd src
		# cvs update -d -P crypto/dist/ssh usr.bin/ssh
		# cd usr.bin/ssh

		# make cleandir dependall
		# make install

	You also need to have an sshd UID and GID, as well as /var/chroot/sshd
	directory (chroot jail), as below:

		Create a group, with /usr/sbin/groupadd, or vi /etc/group

		sshd:*:16:
		
		Create a user, with vipw, or /usr/sbin/useradd

		sshd:*:16:16::0:0:sshd privsep:/var/chroot/sshd:/sbin/nologin

		Create the directory /var/chroot/sshd
		
	Make sure you have "UsePrivilegeSeparation yes" in your
	/etc/ssh/sshd_config (or it can be commented out, as the default value
	is "yes"), to mitigate future issues.


* NetBSD 1.6 and beta:

	Systems running NetBSD 1.6 beta systems have OpenSSH privilege
	separation turned on by default, follow the workaround section
	as approriate for your environment, and upgrade to source dated
	2002-06-26 (with OpenSSH 3.4) to close this vulnerability.

	NetBSD 1.6 will ship with OpenSSH 3.4, which has a complete fix.

	The following directories need to be updated from the
	netbsd-1-6 CVS branch:
		crypto/dist/ssh
		usr.bin/ssh

	To update from CVS, re-build, and re-install:
		# cd src
		# cvs update -d -P crypto/dist/ssh usr.bin/ssh
		# cd usr.bin/ssh

		# make cleandir dependall
		# make install

	The sshd user, group, and chroot jail directories should already exist
	in a 1.6 installation.

* NetBSD 1.5, 1.5.1, 1.5.2:

	Systems running NetBSD 1.5.* releases dated from before
	2002-06-26 should be upgraded to sources dated 2002-06-26
	or later.  Sources on the branch after that date include changes
	presented in the following advisory:
	 	http://openssh.org/txt/preauth.adv

NOTE: the upgrade process will pull in changes presented in this
	advisory.  Therefore, (1) it won't get you OpenSSH 3.4, (2) It
	won't make your sshd support privilege separation.  If you need
	to enable privilege separation, install OpenSSH from pkgsrc
	(openssh-3.4.0.1).

	The following directories need to be updated from the
	netbsd-1-5 CVS branch:
		crypto/dist/ssh
		usr.bin/ssh

	To update from CVS, re-build, and re-install:
		# cd src
		# cvs update -d -P crypto/dist/ssh usr.bin/ssh
		# cd usr.bin/ssh

		# make cleandir dependall
		# make install


* pkgsrc: (All systems, including NetBSD 1.4.*)

	For a complete fix, openssh-3.4.0.1 or later should be
	installed from pkgsrc/security/openssh.  See above, as well as
	console messages during pkgsrc build, for instructions to enable
	privilege separation functionality.


Thanks To
=========

Markus Friedl and Jun-ichiro itojun Hagino for patches, and initial
advisory text.


Revision History
================

	2002-06-26	Initial release


More Information
================

An up-to-date PGP signed copy of this release will be maintained at
   ftp://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2002-005.txt.asc

Information about NetBSD and NetBSD security can be found at 
http://www.NetBSD.ORG/ and  http://www.NetBSD.ORG/Security/.


Copyright 2002, The NetBSD Foundation, Inc.  All Rights Reserved.

$NetBSD: NetBSD-SA2002-005.txt,v 1.25 2002/06/27 14:27:43 david Exp $





 
< Prev   Next >
    
Partner

 

Latest Features
Peter Smith Releases Linux Network Security Online
Securing a Linux Web Server
Password guessing with Medusa 2.0
Password guessing as an attack vector
Squid and Digest Authentication
Squid and Basic Authentication
Demystifying the Chinese Hacking Industry: Earning 6 Million a Night
Free Online security course (LearnSIA) - A Call for Help
What You Need to Know About Linux Rootkits
Review: A Practical Guide to Fedora and Red Hat Enterprise Linux - Fifth Edition
Yesterday's Edition
Fixing OpenSSL's Heartbleed flaw will take MONTHS, warns Secunia
Even the most secure cloud storage may not be so secure, study finds
Targeted Attack Uses Heartbleed to Hijack VPN Sessions
Partner Sponsor

Community | HOWTOs | Blogs | Features | Book Reviews | Networking
 Security Projects |  Latest News |  Newsletters |  SELinux |  Privacy |  Home
 Hardening |   About Us |   Advertise |   Legal Notice |   RSS |   Guardian Digital
(c)Copyright 2014 Guardian Digital, Inc. All rights reserved.