Cisco IOS Software IP Service Level Agreement Vulnerability

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Updated:November 9, 2014

Document ID:1454785347590903

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Cisco Security Advisory

Cisco IOS Software IP Service Level Agreement Vulnerability

High

Advisory ID:

cisco-sa-20110928-ipsla

First Published:

2011 September 28 16:00 GMT

Last Updated:

2012 September 21 19:19 GMT

Version 2.1:

Final

Workarounds:

See below

Cisco Bug IDs:

CSCtk67073

CVE-2011-3272

CVSS Score:

Base 7.8, Temporal 6.4

CVE-2011-3272

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Summary

The Cisco IOS IP Service Level Agreement (IP SLA) feature contains a denial of service (DoS) vulnerability. The vulnerability is triggered when malformed UDP packets are sent to a vulnerable device. The vulnerable UDP port numbers depend on the device configuration. Default ports are not used for the vulnerable UDP IP SLA operation or for the UDP responder ports.

Cisco has released software updates that address this vulnerability.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110928-ipsla.

Note: The September 28, 2011, Cisco IOS Software Security Advisory bundled publication includes ten Cisco Security Advisories. Nine of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses vulnerabilities in Cisco Unified Communications Manager. Each advisory lists the Cisco IOS Software releases that correct the vulnerability or vulnerabilities detailed in the advisory as well as the Cisco IOS Software releases that correct all vulnerabilities in the September 2011 Bundled Publication.

Individual publication links are in "Cisco Event Response: Semiannual Cisco IOS Software Security Advisory Bundled Publication" at the following link:

http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep11.html

Affected Products

Vulnerable Products
Cisco devices that are running Cisco IOS Software are vulnerable when they are configured for IP SLA, either as responders or as originators of vulnerable IP SLA operations.

To determine the Cisco IOS Software release that is running on a Cisco product, administrators can log in to the device and issue the show version command to display the system banner. The system banner confirms that the device is running Cisco IOS Software by displaying text similar to "Cisco Internetwork Operating System Software" or "Cisco IOS Software." The image name displays in parentheses, followed by "Version" and the Cisco IOS Software release name. Other Cisco devices do not have the show version command or may provide different output.

The following example shows output from a device that runs a Cisco IOS Software image:

Router> show version Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2009 by Cisco Systems, Inc. Compiled Wed 02-Dec-09 17:17 by prod_rel_team !--- output truncated

Additional information about Cisco IOS Software release naming conventions is available in the white paper Cisco IOS and NX-OS Software Reference Guide available at: http://www.cisco.com/web/about/security/intelligence/ios-ref.html.
Products Confirmed Not Vulnerable

No other Cisco products are currently known to be affected by these vulnerabilities.

Details

IP SLA is an embedded agent in Cisco IOS Software designed to measure and monitor common network performance metrics like jitter, latency (delay), and packet loss.

The vulnerability that is described in this document is triggered by malformed IP SLA packets sent to the vulnerable device and port. A vulnerable device can be an IP SLA responder or the source device of a vulnerable IP SLA operation.

This vulnerability is documented in Cisco bug ID CSCtk67073 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2011-3272.

Vulnerable IP SLA Responder Configurations

A device configured either as an IP SLA general responder or a permanent IP SLA UDP responder is vulnerable.

The general responder processes IP SLA control protocol packets on UDP port 1967 and then may dynamically open vulnerable UDP ports according to the IP SLA operations requested using the control protocol. The configuration for a general responder is as follows:
```
ip sla responder 
```
The IP SLA UDP permanent responder is also vulnerable. An example configuration is as follows:
```
ip sla responder udp-echo port 300
```
There is no default UDP port number for the UDP permanent responder

Alternatively, both the general responder and the permanent responder can be identified with the show ip sla responder command. The general responder is vulnerable when it has been enabled. The permanent responder is vulnerable only when it has been enabled and the "udpEcho Responder" is present. In the Following example, the general responder is not vulnerable because it has not been enabled but the permanent responder is vulnerable because it has been enabled with a UDP echo responder:
```
Router# show ip sla responder
        General IP SLA Responder on Control port 1967
General IP SLA Responder is: Disabled

        Permanent Port IP SLA Responder
Permanent Port IP SLA Responder is: Enabled

udpEcho Responder: 
  IP Address             Port
  0.0.0.0                 300
```
Vulnerable IP SLA Source Device Configurations

An IP SLA source device is a Cisco IOS device that has at least one IP SLA operation configured. To be vulnerable a probe originator needs to have at least one scheduled probe that uses either of the following IP SLA operations:
- udp-jitter probe
- udp-echo
A vulnerable IP SLA source device configuration includes all the following commands:
- An ip sla global configuration command to define an IP SLA operation
- Either a udp-echo or a udp-jitter IP SLA configuration command
- An ip sla schedule global configuration command that activates one of the probes that uses a vulnerable IP SLA operation
The following examples show a source device that is configured for IP SLA UDP echo and UDP jitter probes:
```
ip sla 201
 udp-echo 192.168.134.21 201
ip sla schedule 201 start-time now

ip sla 301
 udp-jitter 192.168.134.121 122
ip sla schedule 301 start-time now
```
The destination UDP ports for the probes need to be configured. If the source UDP port is not configured an available port number will be used when the probe is started. A device that originates a vulnerable operation will be vulnerable on the source UDP ports of the probe and a responder will be vulnerable on the destination UDP port used for the probe.

IP SLA probes can be configured using Simple Network Management Protocol (SNMP). In that case, by default, the output of the show running-config command will not include the IP SLA probe configuration. The show ip sla configuration command can be used to verify whether a probe has been configured either by the command line or via SNMP.
```
Router# show ip sla configuration | include operation
Type of operation to perform: udp-jitter
```

Workarounds

There are no workarounds for this vulnerability, but there are mitigations that can be deployed on a general IP SLA responder to reduce the exposure to this vulnerability.

General IP SLA Responder Mitigation

For devices that are configured as general responders, a mitigation is to restrict IP SLA control packets on UDP port 1967 that are addressed to the vulnerable device to permit only trusted probe originators to open UDP ports that could be exploited. This can be accomplished using techniques such as Infrastructure Access list or Control Plane Protection.

For devices configured as general responders, mitigation techniques that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory: http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20110928-ipsla.

IP SLA Permanent Responder Mitigation

For the permanent responder, the mitigation is to filter UDP packets addressed to the configured UDP port of each permanent responder to permit packets from the IP addresses of trusted devices.

IP SLA Source Devices Mitigation

For IP SLA source devices, a mitigation is to allow only UDP packets from trusted devices (that is, devices that are the target of IP SLA operations)

Fixed Software

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.

Additionally, the Cisco IOS Software Checker is available on the Cisco Cisco Security (SIO) portal at http://tools.cisco.com/security/center/selectIOSVersion.x. It provides several features for checking which Security Advisories affect specified versions of Cisco IOS Software.