-
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 https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010227-ios-snmp-ilmi.
-
This section provides details on affected products.
Vulnerable 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
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).
Products Confirmed 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.
No other Cisco products are currently known to be affected by these vulnerabilities.
-
Cisco 1400 and 1700 series.
-
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.
A separate Cisco Security Advisory has been announced regarding additional SNMP vulnerabilities. That advisory, http://www.cisco.com/warp/public/707/ios-snmp-community-vulns-pub.shtml, should be consulted in tandem with this notice.
-
system.sysContact -- The contact information for the
person or organization responsible for managing the device.
-
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.
-
Default workaround for use with releases for which no other
workarounds are effective:
-
Applying access lists to all the interfaces of the vulnerable
device blocking SNMP from all hosts but those authorized to manage the devices.
-
Blocking SNMP access at the edge of the network to prevent
undesirable SNMP traffic from entering the network containing the vulnerable
device.
-
Applying access lists to all the interfaces of the vulnerable
device blocking SNMP from all hosts but those authorized to manage the devices.
-
For affected releases based on IOS 11.1:
-
Remove the view so that the ILMI community cannot be reached:
no snmp-server view *ilmi
-
This configuration will not survive a system reload. The command
must be re-entered after every restart of the system.
-
Remove the view so that the ILMI community cannot be reached:
-
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 reapplied following every system reload of the affected device:
-
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.
-
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.
-
Since this configuration will not survive a system reload, the
command must be reentered after every restart of the system.
-
Expose the undocumented ILMI community string so it can be
modified:
-
For affected releases of IOS 11.2 through 11.3(8) THAT
REQUIRE ATM:
Note: This workaround is not valid for ATM switches such as the LS1010 and 8500 series. See section I for those devices.
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:
-
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
-
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.
-
Create a simple ACL to deny access using the following command. If
"66" is already in use, choose a different two-digit number:
-
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. However, the changes will not persist through a reboot of the device. These instructions must be reapplied following every system reload of the affected device:
-
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.
-
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.
-
This configuration will not survive a system reload. The command
must be reentered after every restart of the system.
-
Expose the undocumented ILMI community string so it can be
modified:
-
For affected releases of IOS 11.3(9) through 12.0(2)T THAT
REQUIRE ATM:
Note: This workaround is not valid for ATM switches such as the LS1010 and 8500 series. This workaround is also not valid for 12.0 releases that are based on 12.0(3)T and higher such as 12.0S. See section I for those devices.
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:
-
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
-
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.
-
Create a simple ACL to deny access using the following command. If
"66" is already in use, choose a different two-digit number:
-
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.
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
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.
-
For affected releases of IOS 12.0(3)T and later NOT REQUIRING
ATM:
-
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.
-
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.
-
Expose the undocumented ILMI community string so it can be
modified:
-
For affected releases of IOS 12.0(3)T and later THAT REQUIRE
ATM:
Note: This section also applies to ATM switch software such as for the LS1010 and the 8500 series. This section also applies to other 12.0 releases that are based on 12.0(3)T and higher such as 12.0S.
The only effective workaround for systems in this category is the default workaround:
-
Applying access lists to all the interfaces of the vulnerable
device blocking SNMP from all hosts but those authorized to manage the devices.
-
Blocking SNMP access at the edge of the network to prevent
undesirable SNMP traffic from entering the network containing the vulnerable
device.
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.
-
Applying access lists to all the interfaces of the vulnerable
device blocking SNMP from all hosts but those authorized to manage the devices.
-
Default workaround for use with releases for which no other
workarounds are effective:
-
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
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 Image or Platform
Availability of Fixed Releases*
11.x-based Releases
Rebuild
Interim**
Maintenance
10.3 and earlier
All
Not Affected
11.0-based Releases
Rebuild
Interim**
Maintenance
11.0
Major GD release for all platforms
11.0(22a)
2001-Mar-19
11.1-based Releases
Rebuild
Interim**
Maintenance
11,1
Major release for all platforms
11.1(24a)
2001-Mar-19
11.1AA
ED release for access servers: 1600, 3200, and 5200 series.
12.1(7)
2001-Feb-26
11.1CA
Platform-specific support for 7500, 7200, 7000, and RSP
11.1(36)CA1
2001-Mar-02
11.1CC
ISP train: added support for FIB, CEF, and NetFlow on 7500, 7200, 7000, and RSP
11.1(36)CC1
2001-Mar-02
11,1CT
Added support for Tag Switching on 7500, 7200, 7000, and RSP
12.0(11)ST2
2001-Feb-26
11.1IA
DistributedDirector only
11.1(28)IA1
2001-Mar-02
11.2-based Releases
Rebuild
Interim**
Maintenance
11.2
Major release, general deployment
11.2(25a)
2001-Mar-05
11.2BC
Platform-specific support for IBM networking, CIP, and TN3270 on 7500, 7000, and RSP
12.1(7)
2001-Feb-26
11.2GS
Early deployment release to support 12000 GSR
12.0(15)S1
2001-Feb-20
11.2P
New platform support
11.2(25a)P
2001-Mar-05
11.2SA
Catalyst 2900XL switch only
12.0(5)WC
2001-Apr-12
11.2WA3
LS1010 ATM switch
12.0(10)W(18b)
12.0(13)W5(19b)
Available
Available
11.2(4)XA
Initial release for the 1600 and 3600
11.2(25a)P
2001-Mar-05
11.2(9)XA
Initial release for the 5300 and digital modem support for the 3600
11.2(25a)P
2001-Mar-5
11.3-based Releases
Rebuild
Interim**
Maintenance
11.3
Major release for all platforms
2001-Mar-05
2001-Mar-05
11.3AA
ED for dial platforms and access servers: 5800, 5200, 5300, 7200
11.3(11a)AA
2001-Mar-05
11.3DA
Early deployment train for ISP DSLAM 6200 platform
12.1(5)DA1
2001-Mar-19
11.3DB
Early deployment train for ISP/Telco/PTT xDSL broadband concentrator platform, (NRP) for 6400
12.1(4)DB1
2001-Feb-27
11.3HA
Short-lived ED release for ISR 3300 (SONET/SDH router)
Not Vulnerable
11.3MA
MC3810 functionality only
11.3(1)MA8
2001-Mar-19
11.3NA
Voice over IP, media convergence, various platforms
12.1(7)
2001-Mar-05
11.3T
Early deployment major release, feature-rich for early adopters
11.3(11b)T1
2001-Mar-05
11.3WA4
Multilayer Switching and Multiprotocol over ATM functionality for LS1010
12.0(10)W(18b)
12.0(13)W5(19b)
Available
Available
Introduction of ubr7246 and 2600
11.3(11b)T1
2001-Mar-05
12.0-based Releases
Rebuild
Interim**
Maintenance
12.0
General deployment release for all platforms
12.0(7.1)
12.0(8)
Available
Available
12.0DA
xDSL support: 6100, 6200
12.0(7.1)T
Available
12.0DB
ISP/Telco/PTT xDSL broadband concentrator platforms
12.1(4)DB1
2001-Feb-26
12.0DC
6400 Access Concentrator
12.1(4)DC2
2001-Feb-26
12.0S
Core/ISP support: GSR, RSP, c7200
12.0(15)S1
2001-Feb-20
12.0SC
Cable/broadband ISP: ubr7200
12.0(15)SC
2001-Mar-05
12.0SL
10000 ESR: c10k
12.0(14)SL1
2001-Feb-26
12.0ST
General deployment release for all platforms
12.0(11)ST2
2001-Feb-26
12.0T
Early Deployment(ED): VPN, Distributed Director, various platforms
12.1(7)
2001-Feb-26
12.0W5
cat8510c, ls1010, cat8510m
12.0(10)W5(18c)
Available
cat8540c, cat8540m
12.0(10)W5(18b)
Available
cat5atm, c6msm
12.0(13)W5(19)
Available
cat2948g-L3
12.0(10)W5(18e)
Available
cat4232
12.0(10)W5(18f)
Available
cat4840g
12.0(10)W5(18)
Available
12.0WT
cat4840g
12.0(13)WT6(1)
2001-Mar-15
12.0XA
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XB
Short-lived early deployment release
12.1(7)
2001-Feb-26
12.0XC
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XD
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XE
Early Deployment (ED): limited platforms
12.1(5c)E8
2001-Mar-5
12.0XF
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XG
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XH
Early Deployment (ED): limited platforms
12.0(4)XH5
2001-Mar-12
12.0XI
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XJ
Early Deployment (ED): limited platforms
12.1(7)
2001-Feb-26
12.0XK
Early Deployment (ED): limited platforms
12.0(7)XK4
2001-Mar-26
12.0XL
Early Deployment (ED): limited platforms
12.0(4)XH5
2001-Mar-12
12.0XM
Short-lived early deployment release
12.1(7)
2001-Feb-26
12.0XN
Early Deployment (ED): limited platforms
12.0XP
Early Deployment (ED): limited platforms
Not Vulnerable
12.0XQ
Short-lived early deployment release
12.1(7)
2001-Feb-26
12.0XR
Short-lived early deployment release
12.1(5)T5
2001-Mar-05
12.0XS
Short-lived early deployment release
12.1(5c)E8
2001-Mar-5
12.0XU
Early Deployment (ED): limited platforms
Not Vulnerable
12.0XV
Short-lived early deployment release
12.1(5)T5
2001-Mar-05
12.0XW
Early Deployment (ED): limited platforms
Not Vulnerable
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.
-
Maintenance - Most heavily tested and highly
recommended release of any label in a given row of the table.
-
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.
-
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.
-
Revision 1.5
2001-March-07
Corrected fixed release versions in table
Revision 1.4
2001-March-02
Corrected fixed release versions in table
Revision 1.3
2001-February-28
Corrected fixed release versions in table, modified workarounds for clarity
Revision 1.2
2001-February-27
Error corrected in Affected Products
Revision 1.1
2001-February-27
Error corrected in Workaround
Revision 1.0
2001-February-27
First interim public version
-
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