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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
(Oracle Issues Fix for Oracle Linux) OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System
SecurityTracker Alert ID:  1035460
SecurityTracker URL:  http://securitytracker.com/id/1035460
CVE Reference:   CVE-2015-5600   (Links to External Site)
Date:  Apr 4 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:   Oracle has issued a fix.

The Oracle Linux advisory is available at:

http://linux.oracle.com/errata/ELSA-2016-3531.html

Vendor URL:  linux.oracle.com/errata/ELSA-2016-3531.html (Links to External Site)
Cause:   Access control error, State error
Underlying OS:  Linux (Oracle)
Underlying OS Comments:  5

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:  [El-errata] ELSA-2016-3531 Important: Oracle Linux 5 openssh security update

Oracle Linux Security Advisory ELSA-2016-3531

http://linux.oracle.com/errata/ELSA-2016-3531.html

The following updated rpms for Oracle Linux 5 have been uploaded to the 
Unbreakable Linux Network:

i386:
openssh-4.3p2-82.0.2.el5.i386.rpm
openssh-askpass-4.3p2-82.0.2.el5.i386.rpm
openssh-clients-4.3p2-82.0.2.el5.i386.rpm
openssh-server-4.3p2-82.0.2.el5.i386.rpm

x86_64:
openssh-4.3p2-82.0.2.el5.x86_64.rpm
openssh-askpass-4.3p2-82.0.2.el5.x86_64.rpm
openssh-clients-4.3p2-82.0.2.el5.x86_64.rpm
openssh-server-4.3p2-82.0.2.el5.x86_64.rpm

ia64:
openssh-4.3p2-82.0.2.el5.ia64.rpm
openssh-askpass-4.3p2-82.0.2.el5.ia64.rpm
openssh-clients-4.3p2-82.0.2.el5.ia64.rpm
openssh-server-4.3p2-82.0.2.el5.ia64.rpm


SRPMS:
http://oss.oracle.com/ol5/SRPMS-updates/openssh-4.3p2-82.0.2.el5.src.rpm



Description of changes:

[4.3p2-82.0.2]
- CVE-2015-5600: MaxAuthTries limit bypass via duplicates in 
KbdInteractiveDevices (John Haxby) [orabug 22985024]
- CVE-2016-3115: missing sanitisation of input for X11 forwarding (John 
Haxby) [orabug 22985024]


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