Cisco 7920 Wireless IP Phone Privileges Escalation and Information Disclosure
20 Nov. 2005
Summary
"The Cisco Wireless IP Phone 7920 is an easy-to-use IEEE 802.11b wireless IP phone that provides comprehensive voice communications in conjunction with Cisco CallManager and Cisco CallManager Express. "
The first vulnerability in Cisco 7920 Wireless IP Phone is an SNMP service with fixed community strings that allow remote users to read, write, and erase the configuration of an affected device. The second vulnerability in Cisco 7920 Wireless IP Phone is an open VxWorks Remote Debugger on UDP port 17185 that may allow an unauthenticated remote user to access debugging information or cause a denial of service.
Vulnerable Systems:
* Cisco 7920 Wireless IP Phone, firmware version 2.0 and prior
Successful exploitation of these vulnerabilities may result in information leakage or denial of service attacks against an affected device. In the case of the Fixed SNMP Community Strings vulnerability, an attack may take the form of erasure or modification of the device configuration and personal user data.
Privileges Escalation:
The Cisco 7920 Wireless IP Phone provides an SNMP service with fixed read-only and read-write community strings of "public" and "private", respectively. These strings cannot be changed by the user and will allow remote users to issue an SNMP GetRequest or SetRequest to the phone. SNMP can be used to retrieve and modify the device configuration, including stored user data such as phone book entries. To address this vulnerability, Cisco has provided updated software that removes the SNMP functionality from this product.
This issue is documented in Cisco bug ID CSCsb75186 (registered customers only) .
Information Disclosure:
The Cisco 7920 Wireless IP Phone listens on UDP port 17185 to allow connections from a VxWorks debugger. This port may allow remote users to collect debugging information or conduct a denial of service attack against an affected device. To address this vulnerability, Cisco has provided updated software that closes UDP port 17185.
This issue is documented in Cisco bug ID CSCsb38210 ( registered customers only) .
Workaround:
* For sites that restrict Cisco 7920 phones to one or more known subnets, Access Control Lists (ACLs) can be used to deny traffic to the affected ports.
The following extended access-list can be adapted to your network. This example assumes that all Cisco 7920 phones are connected to the 192.168.10.0 network and that all SNMP access is to be restricted to a management station with the IP address of 10.1.1.1:
access-list 101 permit udp host 10.1.1.1 192.168.10.0 0.0.0.255 range 161 162
access-list 101 permit udp host 10.1.1.1 192.168.10.0 0.0.0.255 port 17185
access-list 101 deny udp any 192.168.10.0 0.0.0.255 range 161 162
access-list 101 deny udp any 192.168.10.0 0.0.0.255 port 17185
access-list 101 permit ip any any
The access-list must then be applied to all interfaces using configuration commands such as:
interface ethernet 0/0
ip access-group 101 in
* Infrastructure ACLs (iACL)
Although it is often difficult to block traffic transiting your network, it is possible to identify traffic which should never be allowed to target your infrastructure devices and block that traffic at the border of your network. Infrastructure ACLs are considered a network security best practice and should be considered as a long-term addition to good network security as well as a workaround for this specific vulnerability. The white paper entitled "Protecting Your Core: Infrastructure Protection Access Control Lists" presents guidelines and recommended deployment techniques for iACLs: http://www.cisco.com/warp/public/707/iacl.html
