Advisory ID: cisco-sa-20050713-ons
For Public Release 2005 July 13 15:00 UTC (GMT)
The Cisco ONS 15216 OADM (Optical Add/Drop Multiplexer) contains a vulnerability in the handling of telnet sessions that can cause a denial-of-service condition in the management plane. Traffic going through the Cisco ONS 15216 OADM (i.e. transit traffic), is not affected when the management plane is under a denial-of-service condition. However, clearing the denial-of-service condition on the management plane requires resetting the device, which impacts transit traffic.
Cisco has made free software available to address this vulnerability. There are workarounds available to mitigate the effects of the vulnerability (see the Workarounds section).
This advisory is posted at
Only the Cisco ONS 15216 OADM running software release 2.2.2 and earlier is affected by the vulnerability described in this advisory.
To determine your software revision, launch a TL1 session and use the RTRV-NE-GEN command at the TL1 prompt to retrieve the software version information like in the following example:
TID-000 98-06-20 14-30-00 M001COMPLD"VENDOR=CISCO, MODEL=SOADM-1CH-1530.33,
This output shows that ONS 15216 OADM is running software release 2.0.0.
No other Cisco products are currently known to be affected by these vulnerabilities.
Telnet is a protocol used for remote management of network devices. It is defined in RFC 854.
The Cisco ONS15216 OADMs allow service providers to add and drop single to multiple wavelengths from their optical transport network.
The Cisco ONS 15216 OADM has separate management and data planes. The management plane is used to manage the device and is usually connected to a network isolated from the Internet and local to the customer's environment. Traffic being switched and transmitted by the OADM flows through the data plane.
Sending a specially crafted stream of data to a telnet session with the Cisco ONS 15216 OADM can cause the session to lock up, and no further telnet sessions can be established. While the telnet session is locked up, traffic flowing through the data plane is not affected. Please note that a TCP session must have been previously established, i.e. the TCP 3-way handshake must have occurred, for the vulnerability to be triggered. This makes it difficult to spoof the source addresses during an attack.
Restoring communications with the management plane requires reloading the Cisco ONS 15216 OADM. This operation affects traffic flowing through the data plane.
This vulnerability is documented in Cisco bug ID CSCee23360 -- Communications permanently lost after Telnet session closed.
Cisco has not provided scores for the vulnerability in this advisory based on the Common Vulnerability Scoring System (CVSS). At the time of original publication, CVSS scoring in Cisco security publications was not yet adopted
Successful exploitation of the vulnerability described in this document may result in a denial-of-service condition in the management plane that will disable the remote manageability of the Cisco ONS 15216 OADM. Clearing a denial-of-service condition on the management plane will result in a denial-of-service condition in the data plane while the device boots up.
When considering software upgrades, please also consult http://www.cisco.com/en/US/products/products_security_advisories_listing.html 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") for assistance.
The vulnerability described in this advisory is fixed in release 2.2.3 and later of the ONS 15216 OADM software. If you are currently running the identified vulnerable software, you should obtain fixed software, as detailed below.
The effectiveness of any workaround 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 is the most appropriate for use in the intended network before it is deployed.
The Cisco ONG platform provides separate management and data planes. Established networking best practices recommend that the management plane is connected to a private network that is completely isolated from the Internet and that is not reachable by customers' traffic.
If complete management and data plane isolation is not possible it is recommended to use Access Control Lists (ACLs) on neighboring routers to only allow telnet connections to the Cisco ONS 15216 OADM from specific network management stations and IP address ranges. This type of filtering could be implemented as part of an Infrastructure ACL, which is a networking best practice. For more information on iACLs, refer to "Protecting Your Core: Infrastructure Protection Access Control Lists" at http://www.cisco.com/warp/public/707/iacl.html.
Cisco has released free software updates that address these vulnerabilities. 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 Cisco.com Downloads at
Do not contact firstname.lastname@example.org or email@example.com for software upgrades
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 whose Cisco products are provided or maintained through prior or existing agreements 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 who purchase direct from Cisco but do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should acquire 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: firstname.lastname@example.org
Customers should have their product serial number available and be prepared to give the URL of this notice as evidence of entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.
Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.
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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.
Initial public release.