[VulnWatch] Cisco Security Advisory: Access Point Memory Exhaustion from ARP Attacks



-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Cisco Security Advisory:
========================
Access Point Memory Exhaustion from ARP Attacks
===============================================

Advisory ID: cisco-sa-20060112-wireless

http://www.cisco.com/warp/public/707/cisco-sa-20060112-wireless.shtml

Revision 1.0
============

For Public Release 2006 January 12 1600 UTC (GMT)

+----------------------------------------------------------------------

Contents
========

Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures

- -----------------------------------------------------------------------

Summary
=======

A vulnerability exists in Cisco Aironet Wireless Access Points (AP)
running IOS which may allow a malicious user to send a crafted attack
via IP address Resolution Protocol (ARP) to the Access point which will
cause the device to stop passing traffic and/or drop user connections.

Repeated exploitation of this vulnerability will create a sustained DoS
(denial of service).

Cisco has made free software available to address this vulnerability
for affected customers. There are workarounds available to mitigate the
effects of the vulnerability.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20060112-wireless.shtml .

Affected Products
=================

Vulnerable Products
+------------------

This security advisory applies to all Cisco Aironet Wireless Access
Points that run Cisco IOS Software. The affected device types include:

* Cisco Aironet 1400 Series Wireless Bridges
* Cisco Aironet 1300 Series Access Points
* Cisco Aironet 1240AG Series Access Points
* Cisco Aironet 1230AG Series Access Points
* Cisco Aironet 1200 Series Access Points
* Cisco Aironet 1130AG Series Access Points
* Cisco Aironet 1100 Series Access Points
* Cisco Aironet 350 Series Access Points running IOS

Products Confirmed Not Vulnerable
+--------------------------------

* Cisco Wireless devices running a VxWorks based image (Version 12.05
and earlier)

No other Cisco products are currently known to be affected by this
vulnerability.

Details
=======

The Address Resolution Protocol (ARP) is used to dynamically map
physical hardware addresses to an IP address. Network devices and
workstations maintain internal tables in which these mappings are
stored for some period of time.

An attacker, who has successfully associated with a Cisco IOS Wireless
Access Point, may be able to spoof ARP messages to the management
interface on the Access Point. The attacker could add entries to the
ARP table on the device until physical memory has been completely
exhausted. This will leave the device in a state where it is unable to
pass traffic until the device has been reloaded by cycling the power.

After upgrading the Access Point (see Software Versions and Fixes), add
the command L2-FILTER BLOCK-ARP to each radio interface.

EXAMPLE:

!
!
interface Dot11Radio0
l2-filter block-arp
!
!



This vulnerability is documented in the Cisco Bug Toolkit as Bug ID
CSCsc16644.

Impact
======

Successful exploitation of this vulnerability may result in a denial of
service (DoS) impacting the availability of the Wireless Access Point.
Management and packet forwarding services will be unavailable.

Software Versions and Fixes
===========================

This issue is fixed in IOS version 12.3-7-JA2 which is available for
download at http://www.cisco.com/kobayashi/sw-center/sw-wireless.shtml .

It is important to note that in addition to the software upgrade, a
configuration change is also necessary to resolve this vulnerability.
Please see the Details section for information on this configuration
change.

When considering software upgrades, also consult
http://www.cisco.com/go/psirt and any subsequent advisories to determine
exposure and a complete update solution.

In all cases, customers should exercise caution to be certain the
devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported
properly by the new release. If the information is not clear, contact
the Cisco Technical Assistance Center ("TAC") or your contracted
maintenance provider for assistance.

Workarounds
===========

The workaround for this issue is to use Virtual LANs (VLANs) to isolate
wireless clients from the Access Point (AP) management interface. A
wireless VLAN infrastructure can be deployed that places AP management
interfaces in one VLAN and places wireless clients into different VLANs
based on SSID. No wireless clients should be allowed on the same VLAN
as the management interface of the AP. There are several design
considerations that must be accounted for when deploying VLANs on the
wireless network. For a discussion of the prerequisites, design
considerations, and wireless and wired hardware configuration examples
refer to:

Using VLANs with Cisco Aironet Wireless Equipment
http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_example09186a00801d0815.shtml

Additional information is available at:

Configuring VLANs
http://www.cisco.com/en/US/products/hw/wireless/ps4570/products_configuration_guide_chapter09186a0080341d34.html

In this example an existing AP is reconfigured to use VLANs. The AP is
configured in VLAN 10 (the native VLAN) and wireless clients are
configured in VLANS 20 and 30.

Creating VLANs will disable existing SSIDs. So for this example, the
existing SSID was deleted, the VLANs were created, Encryption Mode and
Keys were then set for each VLAN, and SSIDs were created for each VLAN.

!
! Set encryption ciphers and broadcast key rotation
!
interface Dot11Radio0
no ip address
no ip route-cache
!
encryption mode ciphers tkip
!
encryption vlan 10 mode ciphers tkip
! Encryption ciphers are set under the physical radio interface
!
encryption vlan 20 mode ciphers tkip
!
encryption vlan 30 mode ciphers tkip
!
broadcast-key change 43000
!
broadcast-key vlan 10 change 43000
! Broadcast key rotation is set under the physical radio interface
!
broadcast-key vlan 20 change 43000
!
broadcast-key vlan 30 change 43000
!
!
!
! Set the SSID's and their vlans and authentication method
!
ssid ap-devices-only
! each SSID must have a vlan and authentication settings
vlan 10
authentication open eap eap_methods
authentication network-eap eap_methods
authentication key-management wpa
!
ssid red20
vlan 20
authentication open eap eap_methods
authentication network-eap eap_methods
authentication key-management wpa
!
ssid red30
vlan 30
authentication open eap eap_methods
authentication network-eap eap_methods
authentication key-management wpa

!--------------------------
! Consider not configuring an SSID for the native VLAN
! which in this example is VLAN 10. Not configuring an
! SSID for the native VLAN will prevent all wireless
! clients from estabishing management connections to
! the AP
!-------------------------

!

interface Dot11Radio0.10
encapsulation dot1Q 10 native
! AP's are placed in this VLAN
no ip proxy-arp
no ip route-cache
no cdp enable
bridge-group 1
bridge-group 1 spanning-disabled
! If the virtual interfaces are configured via the HTTP GUI
! the bridge-group settings will be configured automatically
!
interface Dot11Radio0.20
encapsulation dot1Q 20
! Clients are placed in this VLAN
no ip route-cache
no cdp enable
bridge-group 20
bridge-group 20 subscriber-loop-control
bridge-group 20 block-unknown-source
no bridge-group 20 source-learning
no bridge-group 20 unicast-flooding
bridge-group 20 spanning-disabled
!
interface Dot11Radio0.30
encapsulation dot1Q 30
! Clients are placed in this VLAN
no ip route-cache
no cdp enable
bridge-group 30
bridge-group 30 subscriber-loop-control
bridge-group 30 block-unknown-source
no bridge-group 30 source-learning
no bridge-group 30 unicast-flooding
bridge-group 30 spanning-disabled
!
interface FastEthernet0
no ip address
no ip route-cache
duplex auto
speed auto
no cdp enable
!
!
! Set the Wired virtual interfaces
!
interface FastEthernet0.10
encapsulation dot1Q 10 native
no ip proxy-arp
no ip route-cache
no cdp enable
bridge-group 1
no bridge-group 1 source-learning
bridge-group 1 spanning-disabled
! If the virtual interfaces are configured via the HTTP GUI
! the bridge-group settings will be configured automatically
!
interface FastEthernet0.20
encapsulation dot1Q 20
no ip route-cache
no cdp enable
bridge-group 20
no bridge-group 20 source-learning
bridge-group 20 spanning-disabled
!
interface FastEthernet0.30
encapsulation dot1Q 30
no ip route-cache
no cdp enable
bridge-group 30
no bridge-group 30 source-learning
bridge-group 30 spanning-disabled
!
!
! The AP's BVI1 IP address must be from the native VLAN's subnet
!
interface BVI1
ip address 192.168.1.40 255.255.255.0
no ip route-cache


Wireless Network Security Best Practices
+---------------------------------------

In addition to the above workarounds and example, Cisco recommends
deploying Wireless network security best practices which are discussed
in the references below:

SAFE: Wireless LAN Security in Depth - version 2
http://www.cisco.com/en/US/netsol/ns340/ns394/ns171/ns128/networking_solutions_white_paper09186a008009c8b3.shtml


Wireless LAN Security Solution for Large Enterprise
http://www.cisco.com/en/US/netsol/ns340/ns394/ns348/ns386/networking_solutions_package.html

Cisco Wireless LAN Security Overview
http://www.cisco.com/en/US/products/hw/wireless/ps430/prod_brochure09186a00801f7d0b.html

Mitigation
+---------

The risk of this issue can be mitigated by requiring all wireless
clients to authenticate with an EAP based authentication protocol such
as EAP-FAST, PEAP, or EAP-TLS. However authenticated users could still
exploit this vulnerability as the mitigation cannot completely
eliminate the vulnerability.

Obtaining Fixed Software
========================

Cisco has made free software available to address this vulnerability
for affected customers. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they
have purchased. By installing, downloading, accessing or otherwise
using such software upgrades, customers agree to be bound by the terms
of Cisco's software license terms found at
http://www.cisco.com/public/sw-license-agreement.html, or as otherwise
set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml .

Do not contact either "psirt@xxxxxxxxx" or "security-alert@xxxxxxxxx"
for software upgrades.

Customers with Service Contracts
================================

Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on Cisco's worldwide
website at http://www.cisco.com.

Customers using Third-party Support Organizations
+------------------------------------------------

Customers whose Cisco products are provided or maintained through prior
or existing agreement with third-party support organizations such as
Cisco Partners, authorized resellers, or service providers should
contact that support organization for guidance and assistance with the
appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or
fix is the most appropriate for use in the intended network before it
is deployed.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.

* +1 800 553 2447 (toll free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac@xxxxxxxxx

Have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
for additional TAC contact information, including special localized
telephone numbers and instructions and e-mail addresses for use in
various languages.

Exploitation and Public Announcements
=====================================

The Cisco PSIRT is not aware of any malicious use of the vulnerability
described in this advisory.

This issue was reported to us by Eric Smith at Bucknell University.

Status of This Notice: FINAL
============================

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 stand-alone copy or Paraphrase of the text of this document that
omits the distribution URL in the following section is an uncontrolled
copy, and may lack important information or contain factual errors.

Distribution
============

This advisory is posted on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/cisco-sa-20060112-wireless.shtml .

In addition to worldwide web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.

* cust-security-announce@xxxxxxxxx
* first-teams@xxxxxxxxx
* bugtraq@xxxxxxxxxxxxxxxxx
* vulnwatch@xxxxxxxxxxxxx
* cisco@xxxxxxxxxxxxxxxxx
* cisco-nsp@xxxxxxxxxxxxxxx
* full-disclosure@xxxxxxxxxxxxxxxxx
* comp.dcom.sys.cisco@xxxxxxxxxxxxxxxxxx

Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing
lists or newsgroups. Users concerned about this problem are encouraged
to check the above URL for any updates.

Revision History
================

+----------------------------------------+
| Revision | | Initial |
| 1.0 | 12-January-2006 | public |
| | | release |
+----------------------------------------+

Cisco Security Procedures
=========================

Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and registering
to receive security information from Cisco, is available on Cisco's
worldwide website at
http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html
This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at
http://www.cisco.com/go/psirt.

+-----------------------------------------------------------------------

All contents are Copyright 1992-2006 Cisco Systems, Inc. All rights
reserved.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.2 (GNU/Linux)

iD8DBQFDxn/tezGozzK2tZARAlO2AKDzt7Sd5/AGp8hfvVGdCCn8RttNdQCfdmy8
jjbWbHEN9O+xStDeHu3172o=
=3qgs
-----END PGP SIGNATURE-----



Relevant Pages

  • RE: VALN hopping
    ... little skeptical if it was only Cisco doing the research into VLAN ... According to Cisco they are a good security measure. ... I don't know of any exploits which enable you to VLAN hop. ... therefore require a Layer 3 device to route traffic between them. ...
    (Security-Basics)
  • Cisco Security Advisory: Access Point Memory Exhaustion from ARP Attacks
    ... Cisco Security Procedures ... interfaces in one VLAN and places wireless clients into different VLANs ... bridge-group 1 spanning-disabled ...
    (Bugtraq)
  • [Full-disclosure] Cisco Security Advisory: Access Point Memory Exhaustion from ARP Attacks
    ... Cisco Security Procedures ... interfaces in one VLAN and places wireless clients into different VLANs ... bridge-group 1 spanning-disabled ...
    (Full-Disclosure)
  • RE: The Trivial Cisco IP Phones Compromise
    ... It seems that dispite repeated efforts to educate Cisco about the ... tout their knee-jerk "firewall" response. ... TFTP is the remote unauthenticated administrative mechanism. ... I will explore the problems with Cisco's VLAN ...
    (Bugtraq)
  • VLANs / Bridging / BPDU
    ... I'm having an issue with using vlans and bridging. ... something that can be fixed in either FreeBSD or in the Cisco IOS. ... So the idea is raw0 (renamed vlan interface) accepts the traffic from ...
    (freebsd-net)