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AUSCERT External Security Bulletin Redistribution
Cisco IOS-XE Fragmented Packet Resource Consumption Vulnerability
31 July 2015
AusCERT Security Bulletin Summary
Product: Cisco IOS-XE Software
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2015-4293
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Cisco IOS-XE Fragmented Packet Resource Consumption Vulnerability
Threat Type: CWE-399: Resource Management Errors
IntelliShield ID: 40215
First Published: 2015 July 29 20:04 GMT
Last Published: 2015 July 29 20:04 GMT
Port: Not available
Urgency: Unlikely Use
Severity: Mild Damage
CVSS Base: 5.0
CVSS Temporal: 4.1
Version Summary: Cisco IOS-XE Software contains a vulnerability that could
allow an unauthenticated, remote attacker to cause a denial of service
condition. Updates are available.
A vulnerability in the packet reassembly subsystem of Cisco IOS-XE could allow
an unauthenticated, remote attacker to consume CPU resources which may lead to
a denial of service (DoS) condition.
The vulnerability is due to an error message that is triggered to the console
and the syslog when a fragmented packet cannot be properly reassembled. When
an affected device fails to successfully perform reassembly, instead of
silently dropping the fragments, the ATTN-3-SYNC_TIMEOUT error message may be
triggered. On a device that is highly loaded, this condition may be leveraged
to consume CPU resources that may be required by another process, resulting in
a temporary halt of the queued process. In some situations this may lead to a
drop of transit traffic. An attacker could trigger this vulnerability by
sending a series of IPv4 or IPv6 fragments, that are designed to trigger the
error message, directly to the affected device.
Cisco IOS-XE devices rate-limit error messages to once every 60 seconds by
Cisco has confirmed the vulnerability and released software updates.
At the time this alert was first published, Cisco IOS-XE Software versions
3.13S and prior were vulnerable. Later versions of Cisco IOS-XE Software may
also be affected.
To exploit the vulnerability, an attacker must send a continuous series of
network packets to a targeted device. Devices that are protected by network
filtering or have access restricted from untrusted networks may be at less
risk of exploitation.
Cisco indicates through the CVSS score that functional exploit code exists;
however, the code is not known to be publicly available.
Cisco has released bug ID CSCuo37957 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 targeted device to stop processing network traffic, resulting in a DoS
The vulnerability is due to improper processing of fragmented packets by
devices running Cisco IOS-XE Software.
An unauthenticated, remote attacker could exploit the vulnerability by sending
a series of malicious IPv4 or IPv6 network packets to a targeted device. The
processing of message fragments could cause the device to perform logging
operations resulting from the large volume of network packets, consuming
additional resources and 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 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 email@example.com.
The security vulnerability applies to the following combinations of products.
Cisco Cisco IOS XE Software 2.1 .0, .1, .2 | 2.2 .1, .2, .3 | 2.3 .0, .0t,
.1t, .2 | 2.4 .0, .1 | 2.5 .0, .1, .2 | 2.6 .0, .1, .2 | 3.10S .0, .0a, .1,
.2, .3 | 3.11S .0, .1, .2 | 3.12S .0, .1 | 3.13S .0
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.
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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