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             AUSCERT External Security Bulletin Redistribution

                               ESB-2015.1678
       Cisco IOS Software UBR Devices IPv6 to IPv4 Subsystem Denial
                         of Service Vulnerability
                               29 June 2015

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Cisco IOS
Publisher:         Cisco Systems
Operating System:  Cisco
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2015-4199  

Original Bulletin: 
   http://tools.cisco.com/security/center/viewAlert.x?alertId=39423

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Vulnerability Alert

Cisco IOS Software UBR Devices IPv6 to IPv4 Subsystem Denial of Service 
Vulnerability

Threat Type: CWE-362: Race Conditions

IntelliShield ID: 39423

Version: 1

First Published: 2015 June 22 14:53 GMT

Last Published: 2015 June 22 14:53 GMT

Port: Not available

CVE: CVE-2015-4199

Urgency: Unlikely Use 

Credibility: Confirmed 

Severity: Mild Damage 

CVSS Base: 5.4 

CVSS Version 2.0

CVSS Temporal: 4.5

Version Summary: Cisco Universal Broadband Routers running Cisco IOS Software
contain a vulnerability that could allow an unauthenticated, remote attacker 
to cause a denial of service condition. Updates are available.

Description

A vulnerability in the IPv6 to IPv4 subsystem of Cisco IOS Software could 
allow an unauthenticated, remote attacker to trigger a Performance Routing 
Engine (PRE) crash on a targeted system, resulting in a denial of service 
(DoS) condition.

The vulnerability is due to a race condition that may cause a NULL pointer to
be freed. An attacker could exploit this vulnerability by submitting crafted 
content to a targeted device designed to trigger a race condition. A 
successful exploit could cause a PRE module on the device to crash, resulting
in a DoS condition.

Cisco has confirmed the vulnerability and released software updates.

Warning Indicators

Cisco UBR devices running Cisco IOS Software are affected.

IntelliShield Analysis

An attacker would need to cause hundreds of IPv6-enabled customer premises 
equipment (CPE) devices to drop and reestablish connectivity with the affected
UBR simultaneously and repeatedly over a period of time. This requirement 
would make it difficult to achieve a successful exploit.

Vendor Announcements

Cisco has released bug ID CSCug47366 for registered users, which contains 
additional details and an up-to-date list of affected product versions.

Impact

An unauthenticated, remote attacker could exploit this vulnerability to cause
a PRE module on an affected device to crash, resulting in a DoS condition.

Technical Information

The vulnerability is due to a race condition that may result in a NULL pointer
being freed on an affected device.

An attacker could exploit this vulnerability by submitting crafted content to
a targeted device designed to trigger a race condition. A successful exploit 
could cause a PRE module on the device to crash, resulting in a DoS condition.

Safeguards

Administrators are advised to apply the appropriate updates.

Administrators are advised to allow only trusted users to have network access.

Administrators can help protect affected systems from external attacks by 
using a solid firewall strategy.

Administrators may consider using IP-based access control lists (ACLs) to 
allow only trusted systems to access the affected systems.

Administrators are advised to monitor affected systems.

Patches/Software

Cisco customers with active contracts can obtain updates through the Software
Center at the following link: Cisco. Cisco customers without contracts can 
obtain upgrades by contacting the Cisco Technical Assistance Center at 
1-800-553-2447 or 1-408-526-7209 or via email at tac@cisco.com.

Alert History

Initial Release

Product Sets

The security vulnerability applies to the following combinations of products.

Primary Products:

Cisco IOS 15.3S 15.3(3)S

Associated Products:

N/A

Alerts and bulletins on the Cisco Security Intelligence Operations Portal are
highlighted by analysts in the Cisco Threat Operations Center and represent a
subset of the comprehensive content that is available through Cisco Security 
IntelliShield Alert Manager Service. This customizable threat and 
vulnerability alert service provides security staff with access to timely, 
accurate, and credible information about threats and vulnerabilities that may
affect their environment.

LEGAL DISCLAIMER

The urgency and severity ratings of this alert are not tailored to individual
users; users may value alerts differently based upon their network 
configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED 
THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF 
GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED 
THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION
IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE
TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES 
THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.

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