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Category:   Device (Storage)  >   QNAP Storage Devices Vendors:   QNAP Systems
(QNAP Systems Issues Fix for QNAP QTS) OpenSSH 'KbdInteractiveDevices' Lets Remote Users Bypass Security Restrictions on the Target System
SecurityTracker Alert ID:  1034134
SecurityTracker URL:  http://securitytracker.com/id/1034134
CVE Reference:   CVE-2015-5600   (Links to External Site)
Date:  Nov 12 2015
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. QNAP QTS is affected.

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:   QNAP Systems has issued a fix for CVE-2015-5600 for QNAP QTS (4.2.0 RC2 (Build 0910)) [in September 2015].

The QNAP Systems advisory is available at:

https://www.qnap.com/i/en/support/con_show.php?cid=85

Vendor URL:  www.qnap.com/i/en/support/con_show.php?cid=85 (Links to External Site)
Cause:   Access control error, State error

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



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