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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
(NetBSD Issues Fix) OpenSSH Lets Local Users Hijack Forwarded X Sessions in Certain Cases
SecurityTracker Alert ID:  1019911
SecurityTracker URL:  http://securitytracker.com/id/1019911
CVE Reference:   CVE-2008-1483   (Links to External Site)
Date:  Apr 22 2008
Impact:   User access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 4.3p2, possibly other versions
Description:   A vulnerability was reported in OpenSSH. A local user can hijack a target user's X session.

If the specified X11 forwarding port is in use via IPv4 but not in use by IPv6, the server does not properly select a different port. A local user can hijack forwarded X connections.

Timo Juhani Lindfors reported this vulnerability.

Impact:   A local user can hijack forwarded X connections.
Solution:   NetBSD has released a fix.

The NetBSD advisory is available at:

ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2008-005.txt.asc

Vendor URL:  www.openssh.org/ (Links to External Site)
Cause:   Access control error
Underlying OS:  UNIX (NetBSD)
Underlying OS Comments:  3.0, 3.1, 4.0

Message History:   This archive entry is a follow-up to the message listed below.
Mar 26 2008 OpenSSH Lets Local Users Hijack Forwarded X Sessions in Certain Cases



 Source Message Contents

Subject:  NetBSD Security Advisory 2008-005: OpenSSH Multiple issues



-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


		 NetBSD Security Advisory 2008-005
		 =================================

Topic:		OpenSSH Multiple issues

Version:	NetBSD-current:		affected
		NetBSD 4.0:		affected
		NetBSD 3.1.*:		affected
		NetBSD 3.1:		affected
		NetBSD 3.0:		affected
		NetBSD 3.0.*:		affected

Severity:	ForceCommand bypass and X11 session hijacking

Fixed:		NetBSD-current:		April 05, 2008
		NetBSD-4 branch:	April 07, 2008
			(4.1 will include the fix)
		NetBSD-4-0 branch:	April 07, 2008
			(4.0.1 will include the fix)
		NetBSD-3-1 branch:	April 08, 2008
			(3.1.2 will include the fix)
		NetBSD-3-0 branch:	April 08, 2008
			(3.0.4 will include the fix)
		NetBSD-3 branch:	April 08, 2008
			(3.2 will include the fix)
		pkgsrc:			openssh-4.7.1nb3 corrects the issue


Abstract
========

Two issues have been found with the version of OpenSSH that ships
with NetBSD 3.x, NetBSD 4.x and NetBSD-current.  The two known security 
issues include X11 session hijacking and a bypass of the ForceCommand 
directive.

These vulnerabilities have been assigned CVE-2008-1483 for the X11 session
hijacking and CVE-2008-1657 for the ForceCommand bypass.


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

The ForceCommand sshd_config(5) directive can be bypassed by authenticated
users by utilising the processing of the ~/.ssh/rc file.  The ForceCommand 
directive was introduced in OpenSSH 4.4 as such only NetBSD-current and 
NetBSD-4 are impacted by this issue.

OpenSSH 4.9 introduced a no-user-rc option to the AuthorizedKeys file
for blocking the processing of user ~/.ssh/rc files.  This has been
introduced in all NetBSD branches and documented in the sshd(8) man page.

The second issue allows local users to hijack forwarded X11 sessions of
other users. 


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

It is recommended that NetBSD users of vulnerable versions update
their binaries.

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

* NetBSD-current:

	Systems running NetBSD-current dated from before 2008-04-05
	should be upgraded to NetBSD-current dated 2008-04-06 or later.

	The following files/directories need to be updated from the
	netbsd-current CVS branch (aka HEAD):
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install

* NetBSD 4.*:

	Systems running NetBSD 4.* sources dated from before
	2008-04-07 should be upgraded from NetBSD 4.* sources dated
	2008-04-08 or later.

	The following files/directories need to be updated from the
	netbsd-4 or netbsd-4-0 branches:
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update -r <branch_name> \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install

* NetBSD 3.*:

	Systems running NetBSD 3.* sources dated from before
	2008-04-08 should be upgraded from NetBSD 3.* sources dated
	2008-04-09 or later.

	The following files/directories need to be updated from the
	netbsd-3, netbsd-3-0 or netbsd-3-1 branches:
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update -r <branch_name> \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install


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

	2008-04-21	Initial release


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

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at 
  ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2008-005.txt.asc

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


Copyright 2008, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2008-005.txt,v 1.1 2008/04/15 20:19:56 adrianp Exp $

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>From security-officer@netbsd.org Mon Apr 21 23:14:17 2008
From: NetBSD Security-Officer <security-officer@netbsd.org>
To: netbsd-announce@NetBSD.org
Subject: NetBSD Security Advisory 2008-005: OpenSSH Multiple issues
Organisation: The NetBSD Foundation, Inc.
Reply-To: NetBSD Security Officer <security-officer@NetBSD.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Status: RO


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


		 NetBSD Security Advisory 2008-005
		 =================================

Topic:		OpenSSH Multiple issues

Version:	NetBSD-current:		affected
		NetBSD 4.0:		affected
		NetBSD 3.1.*:		affected
		NetBSD 3.1:		affected
		NetBSD 3.0:		affected
		NetBSD 3.0.*:		affected

Severity:	ForceCommand bypass and X11 session hijacking

Fixed:		NetBSD-current:		April 05, 2008
		NetBSD-4 branch:	April 07, 2008
			(4.1 will include the fix)
		NetBSD-4-0 branch:	April 07, 2008
			(4.0.1 will include the fix)
		NetBSD-3-1 branch:	April 08, 2008
			(3.1.2 will include the fix)
		NetBSD-3-0 branch:	April 08, 2008
			(3.0.4 will include the fix)
		NetBSD-3 branch:	April 08, 2008
			(3.2 will include the fix)
		pkgsrc:			openssh-4.7.1nb3 corrects the issue


Abstract
========

Two issues have been found with the version of OpenSSH that ships
with NetBSD 3.x, NetBSD 4.x and NetBSD-current.  The two known security 
issues include X11 session hijacking and a bypass of the ForceCommand 
directive.

These vulnerabilities have been assigned CVE-2008-1483 for the X11 session
hijacking and CVE-2008-1657 for the ForceCommand bypass.


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

The ForceCommand sshd_config(5) directive can be bypassed by authenticated
users by utilising the processing of the ~/.ssh/rc file.  The ForceCommand 
directive was introduced in OpenSSH 4.4 as such only NetBSD-current and 
NetBSD-4 are impacted by this issue.

OpenSSH 4.9 introduced a no-user-rc option to the AuthorizedKeys file
for blocking the processing of user ~/.ssh/rc files.  This has been
introduced in all NetBSD branches and documented in the sshd(8) man page.

The second issue allows local users to hijack forwarded X11 sessions of
other users. 


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

There are two possible workarounds currently known for the X11 session 
hijacking issue (CVE-2008-1483).  Administrators can choose to set either of
the two following options in sshd_config(5):

	X11Forwarding no
	AddressFamily inet

It is recommended that NetBSD users of vulnerable versions update
their binaries.

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

* NetBSD-current:

	Systems running NetBSD-current dated from before 2008-04-05
	should be upgraded to NetBSD-current dated 2008-04-06 or later.

	The following files/directories need to be updated from the
	netbsd-current CVS branch (aka HEAD):
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install

* NetBSD 4.*:

	Systems running NetBSD 4.* sources dated from before
	2008-04-07 should be upgraded from NetBSD 4.* sources dated
	2008-04-08 or later.

	The following files/directories need to be updated from the
	netbsd-4 or netbsd-4-0 branches:
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update -r <branch_name> \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install

* NetBSD 3.*:

	Systems running NetBSD 3.* sources dated from before
	2008-04-08 should be upgraded from NetBSD 3.* sources dated
	2008-04-09 or later.

	The following files/directories need to be updated from the
	netbsd-3, netbsd-3-0 or netbsd-3-1 branches:
		crypto/dist/ssh/channels.c
		crypto/dist/ssh/auth-options.c
		crypto/dist/ssh/auth-options.h
		crypto/dist/ssh/session.c
		crypto/dist/ssh/sshd.8
		crypto/dist/ssh/sshd_config.5

	To update from CVS, re-build, and re-install ssh:

		# cd src
		# cvs update -r <branch_name> \
			crypto/dist/ssh/channels.c \
			crypto/dist/ssh/auth-options.c \
			crypto/dist/ssh/auth-options.h \
			crypto/dist/ssh/session.c \
			crypto/dist/ssh/sshd.8 \
			crypto/dist/ssh/sshd_config.5
		# cd ../../usr.bin/ssh
		# make USETOOLS=no cleandir dependall
		# make USETOOLS=no install


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

	2008-04-21	Initial release


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

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at 
  ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2008-005.txt.asc

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


Copyright 2008, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2008-005.txt,v 1.2 2008/04/21 19:06:14 adrianp Exp $

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