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Category:   Device (VoIP/Phone/FAX)  >   Cisco IP Phones Vendors:   Cisco
Cisco 7920 Wireless IP Phone Grants Remote Users SNMP Access, Discloses Debugging Information, and Lets Remote Users Deny Service
SecurityTracker Alert ID:  1015232
SecurityTracker URL:
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Nov 16 2005
Impact:   Denial of service via network, Disclosure of system information, Modification of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): Cisco 7920 Wireless IP Phone, firmware version 2.0 and prior
Description:   A vulnerability was reported in the Cisco 7920 Wireless IP Phone. A remote user can modify the configuration, obtain debugging information, and cause denial of service conditions.

The SNMP service uses fixed community strings that allow a remote user to read, write, and delete the configuration on a target device. Cisco has assigned Cisco bug ID CSCsb75186 to this vulnerability.

The device has an open UDP port (17185) that runs the VxWorks Remote Debugger. A remote user can connect to the port to cause denial of service conditions or obtain debugging information. Cisco has assigned Cisco bug ID CSCsb38210 to this vulnerability.

The vendor credits Shawn Merdinger with reporting this vulnerability.

Impact:   A remote user can view, modify, and delete the configuration.

A remote user can obtain debugging information.

A remote user can cause denial of service conditions.

Solution:   Cisco has issued a fixed version (2.01).

[Editor's note: The SNMP vulnerability was corrected in release 1.0(9).]

The vendor's advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Access control error

Message History:   None.

 Source Message Contents

Subject:  [Full-disclosure] Cisco Security Advisory: Fixed SNMP Communities

Hash: SHA1

Cisco Security Advisory: Fixed SNMP Communities and Open UDP Port in Cisco 7920
Wireless IP Phone

Document ID: 68179

Advisory ID: cisco-sa-20051116-7920

Revision 1.0

For Public Release 2005 November 16 1600 UTC (GMT)

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


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

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


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

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

Affected Products

Vulnerable Products

  * Cisco 7920 Wireless IP Phone, firmware version 2.0 and earlier

Products Confirmed Not Vulnerable

  * Cisco 7920 Wireless IP Phone, firmware version 2.01

No other Cisco products are currently known to be affected by these
vulnerabilities, including other IP telephony products.


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) .


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.

Software Versions and Fixes

Cisco has provided free software to address these vulnerabilities; please
consult the chart below for details.

When considering software upgrades, also consult
and any subsequent advisories to determine exposure and a complete upgrade

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.

|                    | Affected  |   First    |
|    Cisco Bug ID    | Firmware  |   Fixed    |
|                    | Releases  |  Firmware  |
|                    |           |  Release   |
| CSCsb75186 (       | Release   |            |
| registered         | 1.0(8)    | Release    |
| customers only)    | and       | 1.0(9)     |
| (SNMP)             | earlier   |            |
| CSCsb38210 (       | Release   |            |
| registered         | 2.0 and   | Release    |
| customers only)    | earlier   | 2.01       |
| (VxWorks)          |           |            |


  * 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

    The following extended access-list can be adapted to your network. This
    example assumes that all Cisco 7920 phones are connected to the network and that all SNMP access is to be restricted to a
    management station with the IP address of

        access-list 101 permit udp host 
	  range 161 162
        access-list 101 permit udp host 
	  port 17185
        access-list 101 deny udp any range 161 162
        access-list 101 deny udp any 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:

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,
or as otherwise set forth at Downloads at

Do not contact either "" or "" 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

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:

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 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

This vulnerability was reported to Cisco by Shawn Merdinger and will be
disclosed on November 16, 2005 at the CSI 32^nd Annual Computer Security
conference in Washington, DC. The Cisco PSIRT is not aware of any malicious use
of the vulnerability described in this advisory.

Status of This Notice: FINAL


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.


This advisory is posted on Cisco's worldwide website at

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.


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      | 2005-November-16 | 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
. This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at

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Version: GnuPG v1.4.2 (GNU/Linux)

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