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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
(Red Hat Issues Fix) OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System
SecurityTracker Alert ID:  1035339
SecurityTracker URL:  http://securitytracker.com/id/1035339
CVE Reference:   CVE-2015-5600   (Links to External Site)
Date:  Mar 21 2016
Impact:   Host/resource access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  

Description:   A vulnerability was reported in OpenSSH. A remote user can bypass authentication attempt limits on the target system.

A remote user can request the keyboard-interactive authentication option ('KbdInteractiveDevices') to open a large number of keyboard-interactive devices on the target server and perform a brute-force password guessing attack against the target sshd service. The number of password attempts can effectively exceed the 'MaxAuthTries' limit and are permitted to occur until the 'LoginGraceTime' limit is reached or the number of keyboard-interactive devices are used.

Servers that have keyboard-interactive authentication enabled (e.g., FreeBSD in the default configuration) are affected.

A demonstration exploit command is provided:

ssh -l[username] -oKbdInteractiveDevices=`perl -e 'print "pam," x 10000'` [target]

The original advisory is available at:

https://kingcope.wordpress.com/2015/07/16/openssh-keyboard-interactive-authentication-brute-force-vulnerability-maxauthtries-bypass/

kingcope reported this vulnerability.

Impact:   A remote user can bypass authentication attempt limits on the target system.
Solution:   Red Hat has issued a fix.

The Red Hat advisory is available at:

https://rhn.redhat.com/errata/RHSA-2016-0466.html

Vendor URL:  rhn.redhat.com/errata/RHSA-2016-0466.html (Links to External Site)
Cause:   Access control error, State error
Underlying OS:  Linux (Red Hat Enterprise)
Underlying OS Comments:  6

Message History:   This archive entry is a follow-up to the message listed below.
Jul 20 2015 OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System



 Source Message Contents

Subject:  [RHSA-2016:0466-01] Moderate: openssh security update

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

=====================================================================
                   Red Hat Security Advisory

Synopsis:          Moderate: openssh security update
Advisory ID:       RHSA-2016:0466-01
Product:           Red Hat Enterprise Linux
Advisory URL:      https://rhn.redhat.com/errata/RHSA-2016-0466.html
Issue date:        2016-03-21
CVE Names:         CVE-2015-5600 CVE-2016-3115 
=====================================================================

1. Summary:

Updated openssh packages that fix two security issues are now available
for Red Hat Enterprise Linux 6.

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 Desktop (v. 6) - i386, x86_64
Red Hat Enterprise Linux Desktop Optional (v. 6) - i386, x86_64
Red Hat Enterprise Linux HPC Node (v. 6) - x86_64
Red Hat Enterprise Linux HPC Node Optional (v. 6) - x86_64
Red Hat Enterprise Linux Server (v. 6) - i386, ppc64, s390x, x86_64
Red Hat Enterprise Linux Server Optional (v. 6) - i386, ppc64, s390x, x86_64
Red Hat Enterprise Linux Workstation (v. 6) - i386, x86_64
Red Hat Enterprise Linux Workstation Optional (v. 6) - i386, 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)

It was discovered that the OpenSSH sshd daemon did not check the list of
keyboard-interactive authentication methods for duplicates. A remote
attacker could use this flaw to bypass the MaxAuthTries limit, making it
easier to perform password guessing attacks. (CVE-2015-5600)

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/):

1245969 - CVE-2015-5600 openssh: MaxAuthTries limit bypass via duplicates in KbdInteractiveDevices
1316829 - CVE-2016-3115 openssh: missing sanitisation of input for X11 forwarding

6. Package List:

Red Hat Enterprise Linux Desktop (v. 6):

Source:
openssh-5.3p1-114.el6_7.src.rpm

i386:
openssh-5.3p1-114.el6_7.i686.rpm
openssh-askpass-5.3p1-114.el6_7.i686.rpm
openssh-clients-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-server-5.3p1-114.el6_7.i686.rpm

x86_64:
openssh-5.3p1-114.el6_7.x86_64.rpm
openssh-askpass-5.3p1-114.el6_7.x86_64.rpm
openssh-clients-5.3p1-114.el6_7.x86_64.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-server-5.3p1-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux Desktop Optional (v. 6):

i386:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-ldap-5.3p1-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm

x86_64:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-ldap-5.3p1-114.el6_7.x86_64.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux HPC Node (v. 6):

Source:
openssh-5.3p1-114.el6_7.src.rpm

x86_64:
openssh-5.3p1-114.el6_7.x86_64.rpm
openssh-clients-5.3p1-114.el6_7.x86_64.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-server-5.3p1-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux HPC Node Optional (v. 6):

x86_64:
openssh-askpass-5.3p1-114.el6_7.x86_64.rpm
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-ldap-5.3p1-114.el6_7.x86_64.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux Server (v. 6):

Source:
openssh-5.3p1-114.el6_7.src.rpm

i386:
openssh-5.3p1-114.el6_7.i686.rpm
openssh-askpass-5.3p1-114.el6_7.i686.rpm
openssh-clients-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-server-5.3p1-114.el6_7.i686.rpm

ppc64:
openssh-5.3p1-114.el6_7.ppc64.rpm
openssh-askpass-5.3p1-114.el6_7.ppc64.rpm
openssh-clients-5.3p1-114.el6_7.ppc64.rpm
openssh-debuginfo-5.3p1-114.el6_7.ppc64.rpm
openssh-server-5.3p1-114.el6_7.ppc64.rpm

s390x:
openssh-5.3p1-114.el6_7.s390x.rpm
openssh-askpass-5.3p1-114.el6_7.s390x.rpm
openssh-clients-5.3p1-114.el6_7.s390x.rpm
openssh-debuginfo-5.3p1-114.el6_7.s390x.rpm
openssh-server-5.3p1-114.el6_7.s390x.rpm

x86_64:
openssh-5.3p1-114.el6_7.x86_64.rpm
openssh-askpass-5.3p1-114.el6_7.x86_64.rpm
openssh-clients-5.3p1-114.el6_7.x86_64.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-server-5.3p1-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux Server Optional (v. 6):

i386:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-ldap-5.3p1-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm

ppc64:
openssh-debuginfo-5.3p1-114.el6_7.ppc.rpm
openssh-debuginfo-5.3p1-114.el6_7.ppc64.rpm
openssh-ldap-5.3p1-114.el6_7.ppc64.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.ppc.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.ppc64.rpm

s390x:
openssh-debuginfo-5.3p1-114.el6_7.s390.rpm
openssh-debuginfo-5.3p1-114.el6_7.s390x.rpm
openssh-ldap-5.3p1-114.el6_7.s390x.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.s390.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.s390x.rpm

x86_64:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-ldap-5.3p1-114.el6_7.x86_64.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux Workstation (v. 6):

Source:
openssh-5.3p1-114.el6_7.src.rpm

i386:
openssh-5.3p1-114.el6_7.i686.rpm
openssh-askpass-5.3p1-114.el6_7.i686.rpm
openssh-clients-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-server-5.3p1-114.el6_7.i686.rpm

x86_64:
openssh-5.3p1-114.el6_7.x86_64.rpm
openssh-askpass-5.3p1-114.el6_7.x86_64.rpm
openssh-clients-5.3p1-114.el6_7.x86_64.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-server-5.3p1-114.el6_7.x86_64.rpm

Red Hat Enterprise Linux Workstation Optional (v. 6):

i386:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-ldap-5.3p1-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm

x86_64:
openssh-debuginfo-5.3p1-114.el6_7.i686.rpm
openssh-debuginfo-5.3p1-114.el6_7.x86_64.rpm
openssh-ldap-5.3p1-114.el6_7.x86_64.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.i686.rpm
pam_ssh_agent_auth-0.9.3-114.el6_7.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-2015-5600
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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