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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
(Red Hat Issues Fix) OpenSSH X11 Forwarding Flaw Lets Users Bypass Trust Restrictions
SecurityTracker Alert ID:  1035338
SecurityTracker URL:  http://securitytracker.com/id/1035338
CVE Reference:   CVE-2016-1908   (Links to External Site)
Date:  Mar 21 2016
Impact:   Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 7.1p2
Description:   A vulnerability was reported in OpenSSH. A remote authenticated user can bypass security restrictions in certain cases.

A remote authenticated X application can trigger a flaw in the handling of errors when generating authentication cookies for untrusted X11 forwarding to establish a trusted connection to the target local X server when only untrusted X11 forwarding was requested. As a result, the remote X client may gain privileged access to the target local X server.

Thomas Hoger reported this vulnerability.

Impact:   A remote authenticated X client can cause X11 forwarding trust to fallback from untrusted to trusted to gain privileged access to the target local X server.
Solution:   Red Hat has issued a fix.

The Red Hat advisory is available at:

https://rhn.redhat.com/errata/RHSA-2016-0465.html

Vendor URL:  rhn.redhat.com/errata/RHSA-2016-0465.html (Links to External Site)
Cause:   State error
Underlying OS:  Linux (Red Hat Enterprise)
Underlying OS Comments:  7

Message History:   This archive entry is a follow-up to the message listed below.
Jan 19 2016 OpenSSH X11 Forwarding Flaw Lets Users Bypass Trust Restrictions



 Source Message Contents

Subject:  [RHSA-2016:0465-01] Moderate: openssh security update

-----BEGIN PGP SIGNED MESSAGE-----
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=====================================================================
                   Red Hat Security Advisory

Synopsis:          Moderate: openssh security update
Advisory ID:       RHSA-2016:0465-01
Product:           Red Hat Enterprise Linux
Advisory URL:      https://rhn.redhat.com/errata/RHSA-2016-0465.html
Issue date:        2016-03-21
CVE Names:         CVE-2016-1908 CVE-2016-3115 
=====================================================================

1. Summary:

Updated openssh packages that fix two security issues are now available
for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Moderate security
impact. Common Vulnerability Scoring System (CVSS) base scores, which give
detailed severity ratings, are available for each vulnerability from the
CVE links in the References section.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Client (v. 7) - x86_64
Red Hat Enterprise Linux Client Optional (v. 7) - x86_64
Red Hat Enterprise Linux ComputeNode (v. 7) - x86_64
Red Hat Enterprise Linux ComputeNode Optional (v. 7) - x86_64
Red Hat Enterprise Linux Server (v. 7) - ppc64, ppc64le, s390x, x86_64
Red Hat Enterprise Linux Server Optional (v. 7) - ppc64, ppc64le, s390x, x86_64
Red Hat Enterprise Linux Workstation (v. 7) - x86_64
Red Hat Enterprise Linux Workstation Optional (v. 7) - x86_64

3. Description:

OpenSSH is OpenBSD's SSH (Secure Shell) protocol implementation.
These packages include the core files necessary for both the OpenSSH client
and server.

It was discovered that the OpenSSH server did not sanitize data received
in requests to enable X11 forwarding. An authenticated client with
restricted SSH access could possibly use this flaw to bypass intended
restrictions. (CVE-2016-3115)

An access flaw was discovered in OpenSSH; the OpenSSH client did not
correctly handle failures to generate authentication cookies for untrusted
X11 forwarding. A malicious or compromised remote X application could
possibly use this flaw to establish a trusted connection to the local X
server, even if only untrusted X11 forwarding was requested.
(CVE-2016-1908)

All openssh users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues. After installing this
update, the OpenSSH server daemon (sshd) will be restarted automatically.

4. Solution:

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

5. Bugs fixed (https://bugzilla.redhat.com/):

1298741 - CVE-2016-1908 openssh: possible fallback from untrusted to trusted X11 forwarding
1316829 - CVE-2016-3115 openssh: missing sanitisation of input for X11 forwarding

6. Package List:

Red Hat Enterprise Linux Client (v. 7):

Source:
openssh-6.6.1p1-25.el7_2.src.rpm

x86_64:
openssh-6.6.1p1-25.el7_2.x86_64.rpm
openssh-askpass-6.6.1p1-25.el7_2.x86_64.rpm
openssh-clients-6.6.1p1-25.el7_2.x86_64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-keycat-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-6.6.1p1-25.el7_2.x86_64.rpm

Red Hat Enterprise Linux Client Optional (v. 7):

x86_64:
openssh-debuginfo-6.6.1p1-25.el7_2.i686.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-ldap-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.x86_64.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.i686.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.x86_64.rpm

Red Hat Enterprise Linux ComputeNode (v. 7):

Source:
openssh-6.6.1p1-25.el7_2.src.rpm

x86_64:
openssh-6.6.1p1-25.el7_2.x86_64.rpm
openssh-clients-6.6.1p1-25.el7_2.x86_64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-keycat-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-6.6.1p1-25.el7_2.x86_64.rpm

Red Hat Enterprise Linux ComputeNode Optional (v. 7):

x86_64:
openssh-askpass-6.6.1p1-25.el7_2.x86_64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.i686.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-ldap-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.x86_64.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.i686.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.x86_64.rpm

Red Hat Enterprise Linux Server (v. 7):

Source:
openssh-6.6.1p1-25.el7_2.src.rpm

ppc64:
openssh-6.6.1p1-25.el7_2.ppc64.rpm
openssh-askpass-6.6.1p1-25.el7_2.ppc64.rpm
openssh-clients-6.6.1p1-25.el7_2.ppc64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.ppc64.rpm
openssh-keycat-6.6.1p1-25.el7_2.ppc64.rpm
openssh-server-6.6.1p1-25.el7_2.ppc64.rpm

ppc64le:
openssh-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-askpass-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-clients-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-keycat-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-server-6.6.1p1-25.el7_2.ppc64le.rpm

s390x:
openssh-6.6.1p1-25.el7_2.s390x.rpm
openssh-askpass-6.6.1p1-25.el7_2.s390x.rpm
openssh-clients-6.6.1p1-25.el7_2.s390x.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.s390x.rpm
openssh-keycat-6.6.1p1-25.el7_2.s390x.rpm
openssh-server-6.6.1p1-25.el7_2.s390x.rpm

x86_64:
openssh-6.6.1p1-25.el7_2.x86_64.rpm
openssh-askpass-6.6.1p1-25.el7_2.x86_64.rpm
openssh-clients-6.6.1p1-25.el7_2.x86_64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-keycat-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-6.6.1p1-25.el7_2.x86_64.rpm

Red Hat Enterprise Linux Server Optional (v. 7):

ppc64:
openssh-debuginfo-6.6.1p1-25.el7_2.ppc.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.ppc64.rpm
openssh-ldap-6.6.1p1-25.el7_2.ppc64.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.ppc64.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.ppc.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.ppc64.rpm

ppc64le:
openssh-debuginfo-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-ldap-6.6.1p1-25.el7_2.ppc64le.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.ppc64le.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.ppc64le.rpm

s390x:
openssh-debuginfo-6.6.1p1-25.el7_2.s390.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.s390x.rpm
openssh-ldap-6.6.1p1-25.el7_2.s390x.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.s390x.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.s390.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.s390x.rpm

x86_64:
openssh-debuginfo-6.6.1p1-25.el7_2.i686.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-ldap-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.x86_64.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.i686.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.x86_64.rpm

Red Hat Enterprise Linux Workstation (v. 7):

Source:
openssh-6.6.1p1-25.el7_2.src.rpm

x86_64:
openssh-6.6.1p1-25.el7_2.x86_64.rpm
openssh-askpass-6.6.1p1-25.el7_2.x86_64.rpm
openssh-clients-6.6.1p1-25.el7_2.x86_64.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-keycat-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-6.6.1p1-25.el7_2.x86_64.rpm

Red Hat Enterprise Linux Workstation Optional (v. 7):

x86_64:
openssh-debuginfo-6.6.1p1-25.el7_2.i686.rpm
openssh-debuginfo-6.6.1p1-25.el7_2.x86_64.rpm
openssh-ldap-6.6.1p1-25.el7_2.x86_64.rpm
openssh-server-sysvinit-6.6.1p1-25.el7_2.x86_64.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.i686.rpm
pam_ssh_agent_auth-0.9.3-9.25.el7_2.x86_64.rpm

These packages are GPG signed by Red Hat for security.  Our key and
details on how to verify the signature are available from
https://access.redhat.com/security/team/key/

7. References:

https://access.redhat.com/security/cve/CVE-2016-1908
https://access.redhat.com/security/cve/CVE-2016-3115
https://access.redhat.com/security/updates/classification/#moderate

8. Contact:

The Red Hat security contact is <secalert@redhat.com>. More contact
details at https://access.redhat.com/security/team/contact/

Copyright 2016 Red Hat, Inc.
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