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ICMPv6 Router Announcement flooding denial of service affecting multiple systems
From: Marc Heuse <mh () mh-sec de>
Date: Tue, 05 Apr 2011 17:50:55 +0200
This security advisory is released because Microsoft doesnt want to fix
the issue. Cisco did for its IOS and ASA within 3 months.
Title: ICMPv6 Router Announcement flooding denial of service affecting
Date: 05 April 2011
Vendors: Cisco, Juniper, Microsoft, FreeBSD
Affected Products: All Cisco IOS ASA with firmware < November 2010
All Netscreen versions
All Windows versions
All FreeBSD version
Vulnerability: ICMPv6 Router Announcement flooding denial of service
Severity: 7.8 (CVE CVSS Score), local network
CVEs: CVE-2010-4670, CVE-2010-4671, CVE-2010-4669
05 April 2011
When flooding the local network with random router advertisements,
hosts and routers update the network information, consuming all
available CPU resources, making the systems unusable and unresponsive.
As IPv6 and autoconfiguration are enabled by default, all are
affected in their default configuration.
For Windows, a personal firewall or similar security product does not
protect against this attack.
Note: Microsoft does not want to fix this security issue for their
Updating the routing tables and configuring IPv6 addresses take up
all available CPU resources.
Routers and firewalls do not forward traffic.
The denial of service is in affect until the flooding is terminated.
The exact impact differs from the affected system type:
Cisco: 100% traffic loss with autconfiguration active, 80% without.
Netscreen: Only affected when the interface is configured as host, traffic
is forwarded until the neighbor information times out, then the traffic
Windows: 100% CPU, 100% RAM
FreeBSD: 100% CPU, additionally IPv6 support can be lost until reboot
Old Linux kernels are also affected, detailed version information unknown.
On IPv6 networks, hosts automatically find out about available
routers via ICMPv6 router announcements which are sent by the
routers. Additionally, router announcemens are used to replace
DHCP by the so called autoconfiguration feature.
Windows and FreeBSD - like all modern operating systems - enable
IPv6 and autoconfiguration by default and are thereby vulnerable.
A personal firewall will not protect against this attack.
If a system receives a router announcement of a new router, it
updates its routing table with the new router, and if the
autoconfiguration flag is set on the announcement (and the host
is configured to configure its IPv6 address by this mechanism),
the host chooses an IPv6 address from the announced network space.
If a network is flooded with random router announcements, systems
scramble to update their routing tables and configure IPv6
Flood the network with router advertisements coming from different
routers and announcing different network prefixes.
A tool to test for this vulnerability is included in the thc-ipv6
package, called flood_router6.
Cisco: IOS fix CSCti24526 , ASA fix CSCti33534
Linux: fixed prior 2010
Netscreen: Juniper waiting for IETF results for how to fix the issue
Windows: Microsoft made clear that they do not plan to issue a
fix for this security issue.
The procession of router announcements must be disabled.
Please consult your system manual on how to this for your
Alternatively, disable IPv6.
10 July 2010 Microsoft informed
10 July 2010 Cisco informed
01 August 2010 Cisco confirms problem, announces fix for October
12 August 2010 Microsoft confirms vulnerability, states no fix
will be supplied.
22 November 2010 Cisco confirms fixes are available and started to
be deployed in current firmwares
28 December 2010 vendor-sec informed (among other issues)
05 February 2011 FreeBSD informed (made aware via vendor-sec 5 weeks
20 February 2011 Juniper informed
09 March 2011 Juniper confirms problem
01 April 2011 Juniper informs that they work with the IETF to
develop a standard method to cope with this and
mh () mh-sec de
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The contents of this advisory is copyright (c) 2010,2011 by Marc Heuse
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- ICMPv6 Router Announcement flooding denial of service affecting multiple systems Marc Heuse (Apr 06)