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AUSCERT External Security Bulletin Redistribution
Cisco IOS and Cisco IOS XE Software UDP Packet Processing
Denial of Service Vulnerability
7 September 2017
AusCERT Security Bulletin Summary
Product: Cisco IOS and Cisco IOS XE
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2017-6627
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Cisco IOS and Cisco IOS XE Software UDP Packet Processing Denial of Service
Advisory ID: cisco-sa-20170906-ios-udp
First Published: 2017 September 6 16:00 GMT
Version 1.0: Final
Cisco Bug IDs:
Base 5.3 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:X/RL:X/RC:X
A vulnerability in the UDP processing code of Cisco IOS and Cisco IOS XE
Software could allow an unauthenticated, remote attacker to cause the input
queue of an affected system to hold UDP packets, causing an interface queue
wedge and a denial of service (DoS) condition.
The vulnerability is due to Cisco IOS Software application changes that create
UDP sockets and leave the sockets idle without closing them. An attacker could
exploit this vulnerability by sending UDP packets with a destination port of 0
to an affected device. A successful exploit could allow the attacker to cause
UDP packets to be held in the input interfaces queue, resulting in a DoS
condition. The input interface queue will stop holding UDP packets when it
receives 250 packets.
There are workarounds that address this vulnerability.
This advisory is available at the following link:
This vulnerability affects Cisco IOS and Cisco IOS XE Software. For
information about affected software releases, consult the Cisco bug ID(s) at
the top of this advisory.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this
To work around this vulnerability, administrators can set a maximum hold queue
value that is greater than 250 for all device interfaces. The following
example shows how to set the value to 350 by using the hold queue in interface
Router# configure terminal
Router(config)# interface gigabitEthernet 1
Router(config-if)# hold-queue 350 in
Administrators can also configure an access-control list (ACL) that blocks UDP
packets with a destination port of 0 and apply the ACL to all device
interfaces, for example:
Extended IP access list 180
10 deny udp any any eq 0
For information about fixed software releases, consult the Cisco bug ID(s) at
the top of this advisory.
When considering software upgrades, customers are advised to regularly consult
the advisories for Cisco products, which are available from the Cisco Security
Advisories and Alerts page, to determine exposure and a complete upgrade
In all cases, customers should ensure that the devices to be upgraded contain
sufficient memory and confirm that current hardware and software
configurations will continue to be supported properly by the new release. If
the information is not clear, customers are advised to contact the Cisco
Technical Assistance Center (TAC) or their contracted maintenance providers.
Exploitation and Public Announcements
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any
public announcements or malicious use of the vulnerability that is described
in this advisory.
Version Description Section Status Date
1.0 Initial public release. - Final 2017-September-06
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF
GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS
LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO
CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the
distribution URL is an uncontrolled copy and may lack important information or
contain factual errors. The information in this document is intended for end
users of Cisco products.
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