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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20060112-wireless.
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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20060112-wireless.
This section provides details on affected products.
This security advisory applies to all Cisco Aironet Wireless Access Points that run Cisco IOS Software. The affected device types include:
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.
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 ( registered customers only)
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/docs/wireless/access_point/12.3_2_JA/configuration/guide/s32vlan.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.
Vulmon
!
! 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
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
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.
This issue is fixed in IOS version 12.3-7-JA2 which is available for download at http://tools.cisco.com/support/downloads/pub/Redirect.x?mdfid=278875243.
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 upgrade 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.
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.
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Revision 1.0 |
12-January-2006 |
Initial public release |
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