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CA-2003-15 Cisco IOS Interface Blocked by IPv4 Packet
release date: July 16, 2003
Last revised: --
revision history can be found at the end of this file.
Cisco devices running Cisco IOS software and configured to
process Internet Protocol version 4 (IPv4) packets
in many versions of Cisco IOS could allow an intruder
to execute a denial-of-service attack against a vulnerable device.
IOS is a very widely deployed network operating system. A
vulnerability in IOS could allow an intruder to execute a
denial-of-service attack against an affected device. Cisco has
published an advisory on this topic, available at
We strongly encourage sites using IOS to read this document and take
is tracking this issue as VU#411332. This reference number
corresponds to CVE candidate CAN-2003-0567.
specially crafted IPv4 packets to an interface on a
vulnerable device, an intruder can cause the device to stop processing
packets destined to that interface. Quoting from Cisco's advisory:
device receiving these specifically crafted IPv4 packets will force
the inbound interface to stop processing traffic. The device may stop
processing packets destined to the router, including routing protocol
packets and ARP packets. No alarms will be triggered, nor will the
router reload to correct itself. This issue can affect all Cisco
devices running Cisco IOS software. This vulnerability may be
exercised repeatedly resulting in loss of availability until a
workaround has been applied or the device has been upgraded to a fixed
version of code."
patch from Cisco
a patch as described in Cisco's Advisory.
a patch can be applied, you can mitigate the risks presented by
this vulnerability by judicious use of access control lists (ACLs).
The correct use of ACLs depends of your network topology.
Additionally, ACLs may degrade performace on some systems. We
recommend reviewing the following before applying ACLs
Coordination Center thanks Cisco Systems of for notifying us
about this problem and for helping us to construct this advisory.
about this advisory may be directed to the author, Shawn
is available from:
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
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during other hours, on U.S. holidays, and on weekends.
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2003 Carnegie Mellon University.
July 16, 2003: Initial release
Version: PGP 6.5.8
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