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2015-10 Security Bulletin: Junos: OpenSSH brute force keyboard interactive MaxAuthTries bypass (CVE-2015-5600)



Article ID: JSA10697 SECURITY_ADVISORIES Last Updated: 14 Oct 2015Version: 1.0
Product Affected:
This issue can affect any product or platform running Junos OS.​
A vulnerability in OpenSSH may allow a remote network based attacker to effectively bypass restrictions on number of authentication attempts, as defined by MaxAuthTries settings on Junos. This may enable brute force password attacks to gain access to the device.

The PAM (Pluggable Authentication Modules) library provides a flexible framework for user authentication and session setup / teardown. It is used not only in the base system, but also by a large number of third-party applications.

Various authentication methods (UNIX, LDAP, Kerberos etc.) are implemented in modules which are loaded and executed according to predefined, named policies. These policies are defined in /etc/pam.conf, /etc/pam.d/<policy name>, /usr/local/etc/pam.conf or /usr/local/etc/pam.d/<policy name>.

The PAM API is a de facto industry standard which has been implemented by several parties. FreeBSD uses the OpenPAM implementation.

This issue is assigned CVE-2015-5600.

The following software releases have been updated to resolve this specific issue: Junos OS 12.1X44-D55, 12.1X46-D40, 12.1X47-D30*, 12.3R11, 12.3X48-D20*, 13.2X51-D40*, 13.2X52-D30, 13.3R8, 14.1R6, 14.2R5, 15.1F3, 15.1F2-S1, 15.1R2, 15.1X49-D20, 15.1X53-D20, and all subsequent releases.

*upcoming releases.

This issue is being tracked as PR 1106752 and is visible on the Customer Support website.

KB16765 - "In which releases are vulnerabilities fixed?" describes which release vulnerabilities are fixed as per our End of Engineering and End of Life support policies.​​

As a workaround, use access lists or firewall filters to limit access to the device, so that it can only be accessed from trusted hosts. Restrict access to only highly trusted administrators.

Additionally, system administrators may disable password based authentication completely, and implement key based authentication exclusively in their SSH server configuration. This would eliminate the possibility of being ever exposed to password brute force attacks.
How to obtain fixed software:
Security vulnerabilities in Junos are fixed in the next available Maintenance Release of each supported Junos version. In some cases, a Maintenance Release is not planned to be available in an appropriate time-frame. For these cases, Service Releases are made available in order to be more timely. Security Advisory and Security Notices will indicate which Maintenance and Service Releases contain fixes for the issues described. Upon request to JTAC, customers will be provided download instructions for a Service Release. Although Juniper does not provide formal Release Note documentation for a Service Release, a list of "PRs fixed" can be provided on request.

Modification History:
Modification History:

2015-10-14: Initial publication

CVSS Score:
8.1 (CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H)
Severity Level:
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories"

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