Cisco Security Advisory
Cisco ONS 15216 OADM Telnet Denial-of-Service Vulnerability
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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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050713-ons.
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Vulnerable Products
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:
> RTRV-NE-GEN:
::100; TID-000 98-06-20 14-30-00 M001COMPLD"VENDOR=CISCO, MODEL=SOADM-1CH-1530.33, SN=0001,SOFTWARE=2.0.0, SOFTWAREUPDATE=1-3-2001,FIRMWARE=1.2.7, FIRMWAREUPDATE=1-3-2001,CHANNUM=1,LAMBDA1=1530.33,ALM-LOSDROP-WEST-1=ON, ALM-LOSDROP-EAST-1=ON,NAME=SOADM-1,LONGITUDE=100,LATITUDE=45, IPADDRESS=10.0.0.2,IPMASK=255.0.0.0,A_POWER=OPERATING, B_POWER=OPERATING"; This output shows that ONS 15216 OADM is running software release 2.0.0.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by these vulnerabilities.
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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.
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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.
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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.
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The Cisco PSIRT is not aware of any public announcements or 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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