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AUSCERT External Security Bulletin Redistribution
Cisco IOS Software UBR Devices IPv6 to IPv4 Subsystem Denial
of Service Vulnerability
29 June 2015
AusCERT Security Bulletin Summary
Product: Cisco IOS
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2015-4199
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Cisco IOS Software UBR Devices IPv6 to IPv4 Subsystem Denial of Service
Threat Type: CWE-362: Race Conditions
IntelliShield ID: 39423
First Published: 2015 June 22 14:53 GMT
Last Published: 2015 June 22 14:53 GMT
Port: Not available
Urgency: Unlikely Use
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.
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
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.
Cisco UBR devices running Cisco IOS Software are affected.
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.
Cisco has released bug ID CSCug47366 for registered users, which contains
additional details and an up-to-date list of affected product versions.
An unauthenticated, remote attacker could exploit this vulnerability to cause
a PRE module on an affected device to crash, resulting in a DoS condition.
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.
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.
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 firstname.lastname@example.org.
The security vulnerability applies to the following combinations of products.
Cisco IOS 15.3S 15.3(3)S
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THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF
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TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES
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