Cisco Security Advisory-
The Cisco 7920 Wireless IP Phone provides Voice Over IP service via IEEE 802.11b Wi-Fi networks and has a form-factor similar to a cordless phone. This product contains two vulnerabilities:
The first vulnerability 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 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.
Cisco has made free software available to address these vulnerabilities for affected customers. There are workarounds available to mitigate the effects of the vulnerability.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051116-7920.
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Fixed SNMP Community Strings
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) .
VxWorks Debugger Port (wdbrpc, 17185/udp)
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) .
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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:
The access-list must then be applied to all interfaces using configuration commands such as: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
interface ethernet 0/0 ip access-group 101 in
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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
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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.
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Cisco has provided free software to address these vulnerabilities; please consult the chart below for details.
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.
Cisco Bug ID
Affected Firmware Releases
First Fixed Firmware Release
CSCsb75186 ( registered customers only) (SNMP)
Release 1.0(8) and earlier
Release 1.0(9)
CSCsb38210 ( registered customers only) (VxWorks)
Release 2.0 and earlier
Release 2.01
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This vulnerability was reported to Cisco by Shawn Merdinger and will be disclosed on November 16, 2005 at the CSI 32nd Annual Computer Security conference in Washington, DC. The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory.
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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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