[NEWS] Cisco IOS Software Processing of SAA Packets

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To: list@securiteam.com
Date: 18 May 2003 11:05:44 +0200

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  Cisco IOS Software Processing of SAA Packets
------------------------------------------------------------------------

SUMMARY

The Service Assurance Agent (SAA) is the new name for the Response Time
Reporter (RTR) feature.

The router is vulnerable only if the RTR responder is enabled. When the
router receives a malformed RTR packet, it will crash. RTR is disabled by
default. Although RTR was introduced in Cisco IOSŪ Software Release 11.2,
only the following main releases are vulnerable:
  * 12.0S, SC, ST, SL, SP, SX
  * 12.1, E, EA, EC, EX, EY
  * 12.2, DA, S
 
For the complete list, please see the Software Versions and Fixes section.
No other Cisco product is vulnerable.

There is no workaround short of disabling the RTR responder. It is
possible to mitigate the vulnerability by applying the access control list
(ACL) on the router.

DETAILS

Affected Products:
This vulnerability affects the following main Cisco IOS Software releases
(some X releases are also affected, and those details are in the Software
Version and Fixes section).

+-----------------------------------------+
| Major | Vulnerable Releases |
| Release | |
|---------+-------------------------------|
| 12.0S | 15, 16, 17, 18, 19, 21 |
|---------+-------------------------------|
| 12.0SC | 15, 16 |
|---------+-------------------------------|
| 12.0SL | 15, 17, 19 |
|---------+-------------------------------|
| 12.0ST | 16, 17, 18, 19, 20, 21 |
|---------+-------------------------------|
| 12.0SP | 19, 20 |
|---------+-------------------------------|
| 12.0SX | 21 |
|---------+-------------------------------|
| 12.1 | 10, 10a, 11, 11a, 11b, 12, |
| | 12a, 12b, 12c, 13, 14, 14.5 |
|---------+-------------------------------|
| 12.1E | 10, 11b, 11.5 |
|---------+-------------------------------|
| 12.1EA | 8, 9 |
|---------+-------------------------------|
| 12.1EC | 10, 10.5 |
|---------+-------------------------------|
| 12.1EX | 10 |
|---------+-------------------------------|
| 12.1EY | 10 |
|---------+-------------------------------|
| 12.2 | 6.8a, 7, 7a, 7b, 7c |
|---------+-------------------------------|
| 12.2DA | 7, 9.4 |
|---------+-------------------------------|
| 12.2S | 9, 10.5 |
+-----------------------------------------+

No other Cisco products are affected.

Details:
The RTR feature allows you to monitor network performance, network
resources, and applications by measuring response times and availability.
With this feature, you can perform troubleshooting, problem notifications,
and problem analysis based on response time reporter statistics.

A router is vulnerable only if the RTR responder is enabled. In order to
verify this, check the router's configuration. Execute the following
command while logged on a router:

    Router>show rtr responder
         RTR Responder is: Enabled
         Number of control messages received: 0 Number of errors: 0
         Recent sources:
         Recent error sources:

If you notice the line "RTR Responder is: Enabled," then you are
vulnerable.

Alternatively, you can use this procedure:

    Router>show ip socket
         show ip socket
         Proto Remote Port Local Port In Out Stat TTY OutputIF
         ....
          17 0.0.0.0 0 10.0.0.1 1967 0 0 89 0

If you notice a line as in the example above where the router is listening
to the port 1967, then you are vulnerable.

For Cisco IOS Software, this vulnerability is documented as two Cisco Bug
IDs: CSCdx17916 and CSCdx61997.

Impact:
By sending malformed RTR packets, it is possible to crash the router.

Software Versions and Fixes:
By going to the following URL, you can see a complete table of software
versions and fixes:
 
<http://www.cisco.com/warp/public/707/cisco-sa-20030515-saa.shtml#Software> http://www.cisco.com/warp/public/707/cisco-sa-20030515-saa.shtml#Software

Obtaining Fixed Software:
Cisco is offering free software upgrades to remedy this vulnerability for
all affected customers. 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
<http://www.cisco.com/public/sw-license-agreement.html>
http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set
forth at the Cisco Connection Online Software Center at
<http://www.cisco.com/public/sw-center/sw-usingswc.shtm>
http://www.cisco.com/public/sw-center/sw-usingswc.shtm.

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 <http://www.cisco.com> http://www.cisco.com.

Customers whose Cisco products are provided or maintained through prior or
existing agreement with third-party support organizations such as Cisco
Partners, authorized resellers, or service providers should contact that
support organization for assistance with the upgrade, which should be free
of charge.

Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). In those cases, customers may only upgrade to a
later version of the same release as indicated by the applicable row in
the Software Versions and Fixes table.

Cisco 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: tac@cisco.com
 
See <http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml>
http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional
TAC contact information, including special localized telephone numbers and
instructions and e-mail addresses for use in various languages.

Please have your product serial number available and 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@cisco.com" or
"security-alert@cisco.com" for software upgrades.

Workarounds:
There is no workaround short of disabling the RTR responder. It is
possible to mitigate the vulnerability by applying the ACL on the router.

If you want to disable the RTR, you need to execute the following
commands:

    Router#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    Router(config)#no rtr responder
    Router(config)#exit
    Router#copy running-config startup-config

If you want to block all offending packets on your network edge, then you
should create an ACL, or modify an existing one, to contain an entry
resembling:

    Router#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    Router(config)#access-list 101 deny udp any any eq 1967
    Router(config)#interface eth0
    Router(config)#ip access-group 101 in

In this example the interface eth0 is assumed to be facing toward the
network edge. You will have to substitute it for the correct interface on
your router.

This will prevent any packet that is destined to the port 1967/UDP from
entering your network. If you need to enable these packets to traverse
your network, then the ACL must exclude only your internal routers.

In addition to filtering packets at the network edge, you may apply
filtering on the device itself and permit packets only from known good
sources. This will contribute to the overall mitigation of this issue.

    Router#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    Router(config)#access-list 101 permit udp 10.0.0.1 10.0.0.10 eq 1967
    Router(config)#access-list 101 deny udp any 10.0.0.10 eq 1967
    Router(config)#interface eth0
    Router(config)#ip access-group 101 in

In this example, 10.0.0.1 is the legitimate source and 10.0.0.10 is the
address of the router itself.

ADDITIONAL INFORMATION

The information has been provided by <mailto:psirt@cisco.com> Cisco
Systems Product Security Incident Response Team.

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