Cisco IOS Advisory

Here is the official word... - We all agree that ATM is evil (thanks to Chris Wedgewood for those thoughts) and Arron agrees that he won't let Dean wind him up over the respective merits of the larger C and J boxes. (and they promise to conduct this meaningful dialog off-line)

Sender: nobody(a)cisco.com From: Cisco Systems Product Security Incident Response Team To: internal-security-announce(a)cisco.com Cc: psirt(a)cisco.com Subject: Cisco Security Advisory: Cisco IOS Software SNMP Read-Write ILMI Community String Vulnerability Date: Tuesday, 27 Feb 2001 04:00:00 -0500 (EST)

Cisco IOS Software SNMP Read-Write ILMI Community String Vulnerability Revision 1.0: INTERIM For Public Release 2001 February 27 04:00 US/Eastern (UTC+0500) _______________________________________________________________

Summary

Cisco IOS software releases based on versions 11.x and 12.0 contain a defect that allows a limited number of SNMP objects to be viewed and modified without authorization using a undocumented ILMI community string. Some of the modifiable objects are confined to the MIB-II system group, such as "sysContact", "sysLocation", and "sysName", that do not affect the device's normal operation but that may cause confusion if modified unexpectedly. The remaining objects are contained in the LAN-EMULATION-CLIENT and PNNI MIBs, and modification of those objects may affect ATM configuration. An affected device might be vulnerable to a denial-of-service attack if it is not protected against unauthorized use of the ILMI community string.

The vulnerability is only present in certain combinations of IOS releases on Cisco routers and switches. ILMI is a necessary component for ATM, and the vulnerability is present in every IOS release that contains the supporting software for ATM and ILMI without regard to the actual presence of an ATM interface or the physical ability of the device to support an ATM connection.

To remove this vulnerability, Cisco is offering free software upgrades for all affected platforms. The defect is documented in DDTS record CSCdp11863.

In lieu of a software upgrade, a workaround can be applied to certain IOS releases by disabling the ILMI community or "*ilmi" view and applying an access list to prevent unauthorized access to SNMP. Any affected system, regardless of software release, may be protected by filtering SNMP traffic at a network perimeter or on individual devices.

This notice will be posted at http://www.cisco.com/warp/public/707/ios-snmp-ilmi-vuln-pub.shtml.

Affected Products

The vulnerability is present only in certain releases of Cisco IOS Software versions 11.x and 12.0 for router and switch products that include support for Asynchronous Transfer Mode (ATM) networking and Interim Local Management Interface (ILMI), and it is present without regard to any physical capability for supporting an ATM interface.

Cisco IOS Software versions based on 10.3 and earlier do not contain the vulnerability. The defect was introduced in 11.0(0.2). All Cisco IOS software releases of 12.1 and later have been repaired and are not vulnerable to the defect described in this advisory.

To determine the software running on a Cisco product, log in to the device and issue the command "show version" to display the system banner. Cisco IOS software will identify itself as "Internetwork Operating System Software" or simply "IOS (tm)". The image name will be displayed between parentheses, usually on the next line of output, followed by "Version" and the IOS release name. Other Cisco devices will not have the "show version" command or will give different output.

The following example identifies a Cisco product running IOS release 12.0(3) with an installed image name of C2500-IS-L:

Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-IS-L), Version 12.0(3), RELEASE SOFTWARE

The device is not vulnerable to the defect described in this advisory since the model 2500 router is specifically excluded in the list of unaffected products shown below.

Cisco devices that may be running an affected IOS software release include, but are not limited to:

* Cisco 1400 and 1700 series.

* Cisco 2600 (except that c2600-c-mz, c2600-d-mz, c2600-i-mz, c2600-io3-mz, and c2600-ix-mz images are not vulnerable).

* Catalyst 2900 ATM, 2900XL, and 2948g series.

* Cisco 3620 (except that c3620-d-mz, c3620-i-mz, c3620-io3-mz, and c3620-ix-mz images are not vulnerable).

* Cisco 3640 (except that c3640-d-mz, c3640-i-mz, c3640-io3-mz, and c3640-ix-mz images are not vulnerable).

* Cisco 3660 (except that c3660-d-mz, c3660-i-mz, and c3660-ix-mz images are not vulnerable).

* Cisco MC3810 (except that mc3810-i-mz, mc3810-is-mz, mc3810-is56i-mz, and mc3810-js-mz images are not vulnerable).

* Catalyst 4232, 4840g, 5000 RSFC series switches.

* Cisco 4500, 4700, and 5800 DSC series.

* Cisco 6200, 6400 NRP, and 6400 NSP series.

* Catalyst MSM (c6msm), 6000 Hybrid Mode (c6msfc), and 6000 Native Mode (c6sup).

* Cisco RSM, 7000, 7010, 7100, 7200, ubr7200, and 7500 series.

* Catalyst 8510CSR, 8510MSR, 8540CSR, and 8540MSR series.

* Cisco 10000 ESR and 12000 GSR series.

* LS1010 and Cisco 6260-NI2.

* DistributedDirector (except that igs-w3 images are not vulnerable).

Cisco products that are not affected by this vulnerability either because they have no support for ATM and ILMI, or because they do not run IOS include, but are not limited to:

* Catalyst ATM blade (runs possibly affected code, but an SNMP connection to the blade is not possible).

* Cisco 800 and 805 series.

* Cisco Universal Broadband Routers ubr900 and ubr920.

* Cisco 1003, 1004, and 1005 series.

* Cisco 1600, 2500, 2800, 4000 series.

* Cisco 2500 Fixed Frad.

* Cisco 3800 (not to be confused with MC3810).

* Cisco 5100, 5200, and 5300 series access servers.

* Catalyst 6000 Supervisor Module.

* Cisco PIX Firewall.

* Aironet and Cisco/Aironet wireless products.

* CS11000, Cache Engine, LocalDirector, and network scaling products (except that the Distributed Director might be affected).

* VPN products such as Altiga concentrators.

* Host-based network management or access management products.

* Cisco IP Telephony and telephony management software (except those that are hosted on a vulnerable IOS platform).

* Voice gateways and convergence platforms (except those that are hosted on a vulnerable IOS platform).

* Optical switch products such as the ONS 15000 series.

Details

ILMI (Interim Local Management Interface) is an independent industry standard used for configuration of ATM (Asynchronous Transfer Mode) interfaces. The standard specifies the use of mechanisms and formats previously defined by SNMP (Simple Network Management Protocol). Although it is based on SNMP, ILMI communication actually occurs using a transport other than IP (Internet Protocol) that traverses only the physical ATM link. ILMI is essential to functions such as ATM auto-discovery and LANE (LAN Emulation).

SNMP "objects" are variables that are organized into a MIB (Management Information Base). The MIB has a tree structure and contains both operational (read-only) data as well as configuration (read-write) options. By specifying a community string of "ILMI" in an SNMP request, access can be obtained to read the objects in three specific parts of the overall management tree structure on any device affected by this vulnerability: the MIB-II system group, the LAN-EMULATION-CLIENT MIB, and the PNNI (Private Network-to-Network Interface) MIB. A subset of objects in each part can be modified using the same "ILMI" community string.

The MIB-II system group contains basic information about the device itself. The number of objects that can be modified is limited. Examples include:

* system.sysContact: The contact information for the person or organization responsible for managing the device.

* system.sysLocation: A description of the physical location where the device is installed or operating.

* system.sysName: The hostname of the device, how it identifies itself at the console prompt. (This might not be the same name by which the device is known to other hosts on the network.)

Most of the objects in the system MIB are read-only and cannot be changed via SNMP, such as the time elapsed since the previous restart and textual descriptions of the device's hardware and software.

Numerous objects can be viewed in the LAN-EMULATION-CLIENT MIB and PNNI MIB, and modification of some of the read-write objects can have an affect on ATM operation of the device. The objects in the LAN-EMULATION-CLIENT MIB can only be viewed or modified if LANE has already been configured on the device.

Access to SNMP in Cisco IOS software can be limited by applying access control lists (ACLs), by modifying or removing the SNMP view, by removing the community string from the running configuration, or by disabling the SNMP service. Any SNMP query that does not meet the criteria for access is promptly discarded when such protective measures are in place. If a query does meet the criteria for access, then a response is formulated and sent.

It is possible to configure the device so that the ILMI community string is unavailable in all IOS 11.1 and higher releases. The particular method selected to accomplish this depends on the specific IOS release and configuration.

This defect is documented as CSCdp11863. The vulnerability is repaired by imposing a test such that an SNMP request using the "ILMI" community string will only be recognized if it has been transported by ILMI.

ATM functionality was added in various 10.x releases of Cisco IOS software. However, the function containing the defect was introduced when support for ILMI and other ATM features was added in IOS release 11.0(0.2). Therefore, all prior releases are not vulnerable.

Impact

If SNMP requests can be received by an affected device, then certain MIB objects can be viewed without proper authorization, causing a violation of confidentiality.

A subset of the readable MIB objects can be modified without authorization to cause a failure of integrity. For example, the hostname can be modified so as to confuse network adminstrators, or the contact and location information could be changed with a goal of disrupting operations or embarassing whoever is responsible for the device.

Objects in the LAN-EMULATION-CLIENT and PNNI MIBs can be viewed and modified, thus resulting in changes to the operation of ATM functions. If ATM is in use on the device, this may result in a failure of availability.

Any affected device that is not otherwise protected against the receipt of SNMP packets is vulnerable to a denial-of-service (DoS) attack by flooding the SNMP port with read or write requests.

Software Versions and Fixes

The following table summarizes the known affected Cisco IOS software releases and the earliest estimated dates of availability for fixed releases. All dates are tentative and subject to change.

Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. If a device is running an earlier release that is known to be vulnerable, it should be upgraded to at least the indicated version.

When selecting a release, keep in mind the following definitions:

Maintenance Most heavily tested and highly recommended release of any label in a given row of the table.

Rebuild Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair.

Interim Built at regular intervals between maintenance releases and receive less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability. Interim releases are usually not available for customer download via CCO without prior arrangement.

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 TAC for assistance as shown in the following section.

More information on IOS release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.

+===========================================================================+ | Train | Description of | Availability of Fixed Releases* | | | Image or Platform | | +===========================================================================+ | 10.3-based Releases and | | | | | Earlier | Rebuild | Interim** | Maintenance | +===========================================================================+ | 10.3 and | | | | earlier |All |Not affected | +===========================================================================+ | 11.0-based Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | | |11.0(22a) | | | | 11.0 |Major GD release | | | | | |for all platforms |2001-Mar-05 | | | +===========================================================================+ | 11.1-based Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | | |11.1(24a) | | | | 11.1 |Major release for | | | | | |all platforms |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |ED release for | | |12.1(7) | | 11.1AA |access servers: | | | | | |1600, 3200, and | | | | | |5200 series. | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Platform-specific |11.1(36)CA1 | | | | 11.1CA |support for 7500, | | | | | |7200, 7000, and RSP|2001-Mar-02 | | | +----------+-------------------+------------+---------------+---------------+ | |ISP train: added | | | | | |support for FIB, |11.1(36)CC1 | | | | 11.1CC |CEF, and NetFlow on| | | | | |7500, 7200, 7000, |2001-Mar-02 | | | | |and RSP | | | | +----------+-------------------+------------+---------------+---------------+ | |Added support for |12.0(11)ST2 | | | | 11.1CT |Tag Switching on | | | | | |7500, 7200, 7000, | | | | | |and RSP |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | | |11.1(28)IA1 | | | | 11.1IA |DistributedDirector| | | | | |only |2001-Feb-26 | | | +===========================================================================+ | 11.2-based Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | | |11.2(25a) | | | | 11.2 |Major release, | | | | | |general deployment |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |Platform-specific | | | | | |support for IBM | | |12.1(7) | | 11.2BC |networking, CIP, | | | | | |and TN3270 on 7500,| | |2001-Feb-26 | | |7000, and RSP | | | | +----------+-------------------+------------+---------------+---------------+ | |Early deployment |12.0(15)S1 | | | | 11.2GS |release to support | | | | | |12000 GSR |2001-Feb-20 | | | +----------+-------------------+------------+---------------+---------------+ | | |11.2(25a)P | | | | 11.2P |New platform | | | | | |support |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | | | | |12.1WC | | 11.2SA |Catalyst 2900XL | | | | | |switch only | | |2001-Apr-12 | +----------+-------------------+------------+---------------+---------------+ | | | | |12.0(10)W5(18c)| | 11.2WA3 |LS1010 ATM switch | | | | | | | | |Available | +----------+-------------------+------------+---------------+---------------+ | | |11.2(25a)P | | | |11.2(4)XA |Initial release for| | | | | |the 1600 and 3600 |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |Initial release for| | | | | |the 5300 and |11.2(9)XA1 | | | |11.2(9)XA |digital modem | | | | | |support for the |Unscheduled | | | | |3600 | | | | +===========================================================================+ | 11.3-based Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | | |11.3(11b) | | | | 11.3 |Major release for | | | | | |all platforms |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |ED for dial | | | | | |platforms and |11.3(11a)AA | | | | 11.3AA |access servers: | | | | | |5800, 5200, 5300, |2001-Mar-05 | | | | |7200 | | | | +----------+-------------------+------------+---------------+---------------+ | |Early deployment |12.1(5)DA1 | | | | 11.3DA |train for ISP DSLAM| | | | | |6200 platform |2001-Feb-28 | | | +----------+-------------------+------------+---------------+---------------+ | |Early deployment | | | | | |train for |12.1(4)DB1 | | | | |ISP/Telco/PTT xDSL | | | | | 11.3DB |broadband | | | | | |concentrator | | | | | |platform, (NRP) for|2001-Feb-26 | | | | |6400 | | | | +----------+-------------------+------------+---------------+---------------+ | |Short-lived ED | | | 11.3HA |release for ISR |Not Vulnerable | | |3300 (SONET/SDH | | | |router) | | +----------+-------------------+------------+---------------+---------------+ | | |11.3(1)MA8 | | | | 11.3MA |MC3810 | | | | | |functionality only |Unscheduled | | | +----------+-------------------+------------+---------------+---------------+ | |Voice over IP, |12.1(7) | | | | 11.3NA |media convergence, | | | | | |various platforms |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |Early deployment |11.3(11b)T1 | | | | 11.3T |major release, | | | | | |feature-rich for | | | | | |early adopters |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |Multilayer | | | | | |Switching and | | |12.0(14)W5(20) | | |Multiprotocol over | | | | | 11.3WA4 |ATM functionality | | | | | |for Catalyst 5000 | | | | | |RSM, 4500, 4700, | | |2001-Feb-28 | | |7200, 7500, LS1010 | | | | +----------+-------------------+------------+---------------+---------------+ | | |11.3(11b)T1 | | | |11.3(2)XA |Introduction of | | | | | |ubr7246 and 2600 |2001-Mar-05 | | | +===========================================================================+ | 12.0-based Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | |General deployment | |12.0(7.1) |12.0(16) | | 12.0 |release for all | | | | | |platforms | |Available |2001-Feb-20 | +----------+-------------------+------------+---------------+---------------+ | | | |12.0(7.1)T | | | 12.0DA |xDSL support: 6100,| | | | | |6200 | |Available | | +----------+-------------------+------------+---------------+---------------+ | |ISP/Telco/PTT xDSL |12.1(4)DB1 | | | | 12.0DB |broadband | | | | | |concentrator | | | | | |platforms |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.1(4)DC2 | | | | 12.0DC |6400 Access | | | | | |Concentrator |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.0(15)S1 | | | | 12.0S |Core/ISP support: | | | | | |GSR, RSP, c7200 |2001-Feb-20 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.0(15)SC1 | | | | 12.0SC |Cable/broadband | | | | | |ISP: ubr7200 |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.0(14)SL1 | | | | 12.0SL |10000 ESR: c10k | | | | | | |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | |General deployment |12.0(11)ST2 | | | | 12.0ST |release for all | | | | | |platforms |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.1(5c)E8 | | | | 12.0SX |Early Deployment | | | | | |(ED) |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | |Early | | | | | |Deployment(ED): | | |12.1(7) | | 12.0T |VPN, Distributed | | | | | |Director, various | | |2001-Feb-26 | | |platforms | | | | +----------+-------------------+------------+---------------+---------------+ | |cat8510c, cat8540c,| | | | | |ls1010, cat8510m, | |12.0(10)W5(18c)|12.0(14)W5(20) | | |cat8540m, c5atm, | | | | | |c5atm, c3620, | | | | | |c3640, c4500, | | | | | 12.0W5 |c5rsfc, c5rsm, | |Available |2001-Feb-28 | | |c7200, rsp, | | | | | |cat2948g, cat4232 | | | | | +-------------------+------------+---------------+---------------+ | | | |12.0(10)W5(18d)|12.0(14)W5(20) | | |c6msm | | | | | | | |Available |2001-Feb-28 | +----------+-------------------+------------+---------------+---------------+ | |General deployment | | |12.0(13)WT6(1) | | 12.0WT |release for all | | | | | |platforms | | |2001-Feb-20 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XA |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | | | | |12.1(7) | | 12.0XB |Short-lived early | | | | | |deployment release | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XC |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XD |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment |12.1(5c)E8 | | | | 12.0XE |(ED): limited | | | | | |platforms |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XF |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XG |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment |12.0(4)XH5 | | | | 12.0XH |(ED): limited | | | | | |platforms |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XI |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1(7) | | 12.0XJ |(ED): limited | | | | | |platforms | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment |12.0(7)XK4 | | | | 12.0XK |(ED): limited | | | | | |platforms |Unscheduled | | | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment |12.0(4)XH5 | | | | 12.0XL |(ED): limited | | | | | |platforms |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | | | | |12.1(7) | | 12.0XM |Short-lived early | | | | | |deployment release | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | | | | 12.0XN |(ED): limited | | | | | |platforms | | | | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1WC | | 12.0XP |(ED): limited | | | | | |platforms | | |2001-Apr-12 | +----------+-------------------+------------+---------------+---------------+ | | | | |12.1(7) | | 12.0XQ |Short-lived early | | | | | |deployment release | | |2001-Feb-26 | +----------+-------------------+------------+---------------+---------------+ | | |12.1(5)T5 | | | | 12.0XR |Short-lived early | | | | | |deployment release |2001-Mar-05 | | | +----------+-------------------+------------+---------------+---------------+ | | |12.1(5c)E8 | | | | 12.0XS |Short-lived early | | | | | |deployment release |2001-Feb-26 | | | +----------+-------------------+------------+---------------+---------------+ | |Early Deployment | | |12.1WC | | 12.0XU |(ED): limited | | | | | |platforms | | |2001-Apr-12 | +----------+-------------------+------------+---------------+---------------+ | | |12.1(5)T5 | | | | 12.0XV |Short-lived early | | | | | |deployment release |2001-Mar-05 | | | +===========================================================================+ |12.1-based and Later Releases | Rebuild | Interim** | Maintenance | +===========================================================================+ | All 12.1 | | | | Releases |Various platforms |Not Vulnerable | +===========================================================================+ | Notes | +===========================================================================+ | * All dates are estimated and Subject to change. | | | |** Interim releases are subjected to less rigorous testing than regular | | maintenance releases, and may have serious bugs. | +===========================================================================+

Obtaining Fixed Software

Cisco is offering free software upgrades to remedy this vulnerability for all affected customers. Customers with service contracts may upgrade to any software release. Customers without contracts may upgrade only within a single row of the table above, except that any available fixed software release will be provided to any customer who can use it and for whom the standard fixed software release is not yet available. Customers may install only the feature sets they have purchased.

Note that not all fixed software may be available as of the release date of this notice.

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained via Cisco's Software Center at http://www.cisco.com/.

Customers without contracts or warranty should get their upgrades by contacting the Cisco Technical Assistance Center (TAC) as shown below: * (800) 553-2447 (toll-free in North America) * +1 408 526 7209 (toll call from anywhere in the world) * e-mail: tac(a)cisco.com

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including instructions and e-mail addresses for use in various languages.

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. Please do not contact either "psirt(a)cisco.com" or "security-alert(a)cisco.com" for software upgrades; faster results will be obtained by contacting the TAC directly.

Workarounds

Several workarounds are available based on customer needs, equipment, and software features. The usefulness and practicality of each workaround depends on the IOS release running on the device and many variables in the customer's environment. Customers are urged to consider each of the following alternatives carefully before deploying. These workarounds are only needed if it is not possible to upgrade to an unaffected release of IOS software.

A. Default workaround for use with releases for which no other workarounds are effective:

1. Applying access lists to all the interfaces of the vulnerable device blocking SNMP from all hosts but those authorized to manage the devices.

2. Blocking SNMP access at the edge of the network to prevent undesirable SNMP traffic from entering the network containing the vulnerable device.

Access lists should be deployed with careful consideration of the possible effects on network operation and performance. Also note that authentication based on an IP source address is weak, so the preceding method will not protect against certain types of attacks in which the IP source address has been spoofed. Further information can be found in the Cisco document "Improving Security on Cisco Routers", available at http://www.cisco.com/warp/public/707/21.html

B. For affected releases based on IOS 11.1:

1. Remove the view so that the ILMI community cannot be reached:

no snmp-server view *ilmi

2. This configuration will not survive a system reload. The command must be re-entered after every restart of the system.

C. For affected releases of IOS 11.2 through 11.3(8) NOT REQUIRING ATM:

In this affected range of releases, the ILMI community string can be modified or deleted. However, the changes will not persist through a reboot of the device. These instructions must be re-applied following every system reload of the affected device:

1. Expose the undocumented ILMI community string so it can be modified:

snmp-server community ILMI RW

The preceding command may cause an error that can be safely ignored.

2. Disable read-write capability for the same community:

no snmp-server community ILMI RW

If an error is displayed, then this workaround cannot be applied to the device. Use the default workarounds presented in the first item above.

3. Since this configuration will not survive a system reload, the command must be re-entered after every restart of the system.

If the command in item 2 above did not generate an error and ATM is not needed on this device, then this workaround is complete.

D. For affected releases of IOS 11.2 through 11.3(8) THAT REQUIRE ATM:

This workaround will allow ILMI to continue to function for ATM while constraining who may reconfigure the device by way of the ILMI community string:

1. Create a simple ACL to deny access using the following command. If "66" is already in use, choose a different two-digit number:

access-list 66 deny any

2. Apply it generally to the ILMI community to restrict its view:

snmp community ILMI view *ilmi RW 66

An error will be reported if the *ilmi view doesn't exist. If that occurs, then use the following command to explicitly restrict the ILMI view:

snmp community ILMI RW 66

If the preceding command produces persistent errors, then this workaround cannot be applied to this device. Use the default workarounds presented in the first item above.

E. For affected releases of IOS 11.3(9) through 12.0(2)T NOT REQUIRING ATM:

All versions of IOS in this range will accept this workaround, and the change will remain in place after a system reload.

1. Expose the undocumented ILMI community string so it can be modified:

snmp-server community ILMI RW

The preceding command may cause an error that can be safely ignored.

2. Disable read-write capability for the same community:

no snmp-server community ILMI RW

If an error is displayed, then this workaround cannot be applied to the device. Stop this procedure and use the default workarounds presented in the first item above.

F. For affected releases of IOS 11.3(9) through 12.0(2)T THAT REQUIRE ATM:

This workaround will allow ILMI to continue to function for ATM while constraining who may reconfigure the device by way of the ILMI community string:

1. Create a simple ACL to deny access using the following command. If "66" is already in use, choose a different two-digit number:

access-list 66 deny any

2. Apply it generally to the ILMI community to restrict its view:

snmp community ILMI view *ilmi RW 66

An error will be reported if the *ilmi view doesn't exist. If that occurs, then use the following command to explicitly restrict the ILMI view:

snmp community ILMI RW 66

If the preceding command produces persistent errors, then this workaround cannot be applied to this device. Use the default workaround presented in the first item above.

G. For affected releases of IOS 12.0(3)T and later: These releases of IOS include support for Simple Network Management Protocol version 3 (SNMPv3), which is required for this workaround.

1. Confirm the presence of SNMPv3 support by asking the console CLI (command-line interpreter) for assistance with options to complete the snmp-server command. Enter config mode, enter the command shown below, and note the expected response:

snmp-server user test test ?

remote Specify a remote SNMP entity to which the user belongs v1 user using the v1 security model v2c user using the v2c security model v3 user using the v3 security model

If the preceding command did not produce the expected results, then SNMPv3 is not supported in the release and this workaround cannot be applied. Stop this procedure and consider applying the default workaround presented above in the first item.

Otherwise, if the device responded as expected, continue with the following explanation and instructions.

In these IOS releases (12.0(3)T and later), ILMI packets are processed by the SNMP engine in the same manner as ordinary IP SNMP packets. An access control list or a view applied to the ILMI community string will be processed whether the transport is ILMI or IP. However, the only types of access control lists that can be applied to a community string are via IP access-list statements, which when applied, block ALL non-IP packets, including ILMI packets. Modifying or deleting the *ilmi view will also affect the packets transported by ILMI, so workarounds that change the view are equally ineffective at permitting ILMI while denying SNMP. In this range of releases, it is not possible to apply a workaround that denies IP SNMP packets that does not also deny ILMI SNMP packets.

H. For affected releases of IOS 12.0(3)T and later NOT REQUIRING ATM:

1. Expose the undocumented ILMI community string so it can be modified:

snmp-server community ILMI RW

The preceding command may cause an error that can be safely ignored.

2. Disable read-write capability for the same community:

no snmp-server community ILMI RW

If an error is displayed, then this workaround cannot be applied to the device. Stop this procedure and consider using the default workaround.

I. For affected releases of IOS 12.0(3)T and later THAT REQUIRE ATM:

NOTE: This section also applies to 12.0-based ATM switch software such as for the LS1010 and the 8500 series.

The only effective workaround for systems in this category is the default workaround:

1. Applying access lists to all the interfaces of the vulnerable device blocking SNMP from all hosts but those authorized to manage the devices.

2. Blocking SNMP access at the edge of the network to prevent undesirable SNMP traffic from entering the network containing the vulnerable device.

Access lists should be deployed with careful consideration of the possible effects on network operation and performance. Also note that authentication based on an IP source address is weak, so the preceding method will not protect against certain types of attacks in which the IP source address has been spoofed. In this range of releases it is not possible to block IP SNMP packets while permitting ILMI SNMP packets. The alternative workarounds presented previously will almost certainly cause a failure of ATM ILMI communications resulting in a loss of ATM connectivity, either immediately upon configuration, or unexpectedly at some later time. Either use the default workaround or upgrade to fixed software.

Exploitation and Public Announcements

This vulnerability is known to the engineering staff of several Cisco customers. Cisco considers it known to the public prior to the publication of this notice.

Cisco is aware of one recent incident involving the unauthorized modification of a router that appears to have resulted from this vulnerability. However, it may have been the unintended side-effect of a test of the vulnerability.

Cisco is not aware of any available tools specifically designed to make use of this vulnerability. However, various off-the-shelf network management programs could easily be used to test for this vulnerability and to exploit it. Certain widely-available programs known to the cracker community could be modified by any reasonably competent programmer to automate the abuse of this vulnerability.

Cisco is not aware of any general public discussion of this vulnerability other than the exceptions previously noted.

Status of This Notice: INTERIM

This is an interim security advisory. Cisco anticipates issuing updated versions of this notice at irregular intervals as there are material changes in the facts, and will continue to update this notice as necessary. The reader is warned that this notice may contain inaccurate or incomplete information. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco anticipates issuing monthly updates of this notice until it reaches FINAL status.

A standalone copy or paraphrase of the text of this security advisory that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

Distribution

This notice will be posted at http://www.cisco.com/warp/public/707/ios-snmp-ilmi-vuln-pub.shtml .

In addition to Worldwide Web posting, a text version of this notice will be clear-signed with the Cisco PSIRT PGP key and will be posted to the following e-mail and Usenet news recipients:

* cust-security-announce(a)cisco.com

* bugtraq(a)securityfocus.com

* firewalls(a)lists.gnac.com

* first-teams(a)first.org (including CERT/CC)

* cisco(a)spot.colorado.edu

* cisco-nsp(a)puck.nether.net

* comp.dcom.sys.cisco

* Various internal Cisco mailing lists

Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates.

Revision History

Revision 1.0 2001-Feb-27 First interim public version

Cisco Product Security Incident Procedures

Instructions for reporting product security vulnerabilities in Cisco products, obtaining assistance with customer security incidents, and registering to receive security information from Cisco can be found at http://www.cisco.com/warp/public/707/sec_incident_response.shtml , including instructions for press inquiries regarding Cisco Security Advisories. _______________________________________________________________

Copyright 2001 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, and include all date and version information. _______________________________________________________________

-- \_ Roger De Salis Cisco Systems NZ Ltd