Hash: SHA1

             AUSCERT External Security Bulletin Redistribution

     ESB-2004.0296 -- US-CERT Technical Cyber Security Alert TA04-111B
               Cisco IOS SNMP Message Handling Vulnerability
                               22 April 2004


        AusCERT Security Bulletin Summary

Product:                Cisco routers and switches running IOS trains
                        12.0S, 12.1E, 12.2, 12.2S, 12.3, 12.3B and 12.3T
Publisher:              US-CERT
Impact:                 Denial of Service
Access Required:        Remote

- --------------------------BEGIN INCLUDED TEXT--------------------

Hash: SHA1

Cisco IOS SNMP Message Handling Vulnerability

   Original release date: April 20, 2004
   Last revised: --
   Source: US-CERT

Systems Affected

     * Cisco routers and switches running vulnerable versions of IOS.
       Vulnerable IOS versions known to be affected include:

     * 12.0(23)S4, 12.0(23)S5
     * 12.0(24)S4, 12.0(24)S5
     * 12.0(26)S1
     * 12.0(27)S
     * 12.0(27)SV, 12.0(27)SV1
     * 12.1(20)E, 12.1(20)E1, 12.1(20)E2
     * 12.1(20)EA1
     * 12.1(20)EW, 12.1(20)EW1
     * 12.1(20)EC, 12.1(20)EC1
     * 12.2(12g), 12.2(12h)
     * 12.2(20)S, 12.2(20)S1
     * 12.2(21), 12.2(21a)
     * 12.2(23)
     * 12.3(2)XC1, 12.3(2)XC2
     * 12.3(5), 12.3(5a), 12.3(5b)
     * 12.3(6)
     * 12.3(4)T, 12.3(4)T1, 12.3(4)T2, 12.3(4)T3
     * 12.3(5a)B
     * 12.3(4)XD, 12.3(4)XD1


   There is a vulnerability in Cisco's Internetwork Operating System
   (IOS) SNMP service. When vulnerable Cisco routers or switches process
   specific SNMP requests, the system may reboot. If repeatedly
   exploited, this vulnerability could result in a sustained denial of
   service (DoS).

   This vulnerability is distinct from the vulnerability described in
   US-CERT Technical Alert TA04-111A issued earlier today. Cisco has
   published an advisory about this distinct SNMP issue at the following


I. Description

   The Simple Network Management Protocol (SNMP) is a widely deployed
   protocol that is commonly used to monitor and manage network devices.
   There are several types of SNMP messages that are used to request
   information or configuration changes, respond to requests, enumerate
   SNMP objects, and send both solicited and unsolicited alerts. These
   messages use UDP to communicate network information between SNMP
   agents and managers.

   There is a vulnerability in Cisco's IOS SNMP service in which attempts
   to process specific SNMP messages are handled incorrectly. This may
   potentially cause the device to reload.

   Typically, ports 161/udp and 162/udp are used during SNMP operations
   to communicate. In addition to these well-known ports, Cisco IOS uses
   a randomly selected UDP port in the range from 49152/udp to 59152/udp
   (and potentially up to 65535) to listen for other types of SNMP
   messages. While SNMPv1 and SNMPv2c formatted messages can trigger this
   vulnerability, the greatest risk is exposed when any SNMPv3 solicited
   operation is sent to a vulnerable port.

   Cisco notes in their advisory:

   "SNMPv1 and SNMPv2c solicited operations to the vulnerable ports will
       perform an authentication check against the SNMP community string,
       which may be used to mitigate attacks. Through best practices of
       hard to guess community strings and community string ACLs, this
       vulnerability may be mitigated for both SNMPv1 and SNMPv2c.
       However, any SNMPv3 solicited operation to the vulnerable ports
       will reset the device. If configured for SNMP, all affected
       versions will process SNMP version 1, 2c and 3 operations."

   Cisco is tracking this issue as CSCed68575. US-CERT is tracking this
   issue as VU#162451.

II. Impact

   A remote, unauthenticated attacker could cause the vulnerable device
   to reload. Repeated exploitation of this vulnerability could lead to a
   sustained denial of service condition.

III. Solution

Upgrade to fixed versions of IOS

   Cisco has published detailed information about upgrading affected
   Cisco IOS software to correct this vulnerability. System managers are
   encouraged to upgrade to one of the non-vulnerable releases. For
   additional information regarding availability of repaired releases,
   please refer to the "Software Versions and Fixes" section of the Cisco
   Security Advisory.



   Cisco recommends a number of workarounds, including disabling SNMP
   processing on affected devices. For a complete list of workarounds,
   see the Cisco Security Advisory.

Appendix A. Vendor Information

   This appendix contains information provided by vendors for this
   advisory. As vendors report new information to US-CERT, we will update
   this section and note the changes in our revision history. If a
   particular vendor is not listed below, we have not received their

Cisco Systems

   Please refer to Cisco Security Advisory: "Vulnerabilities in SNMP
   Message Processing". Cisco has published their advisory at the
   following location:


   US-CERT thanks Cisco Systems for notifying us about this problem.

   Feedback can be directed to the authors: Jeff Havrilla, Shawn Hernan,
   Damon Morda

   The latest version of this document can be found at:


   Copyright 2004 Carnegie Mellon University.

   Terms of use:

   Revision History

   April 20, 2004: Initial release

Version: GnuPG v1.2.1 (GNU/Linux)


- --------------------------END INCLUDED TEXT--------------------

You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.

This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:


If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:


Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business 
                hours which are GMT+10:00 (AEST).  On call after hours 
                for member emergencies only.
Comment: http://www.auscert.org.au/render.html?it=1967