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Nokia SGSN (DX200 Based Network Element) SNMP issue
From: "@stake Advisories" <advisories () atstake com>
Date: Thu, 13 Mar 2003 12:03:56 -0500

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                             @stake, Inc.
                           www.atstake.com

                          Security Advisory

Advisory Name: Nokia SGSN (DX200 Based Network Element) SNMP issue
Release Date: 03/13/2003
 Application: Nokia SGSN (DX200 Based Network Element)
    Platform: DX200
    Severity: An attacker is able to read SNMP options with any
              community string
      Author: Ollie Whitehouse [ollie () atstake com]
Vendor Status: Vendor has removed support for this protocol
CVE Candidate: CVE Candidate number applied for
   Reference: www.atstake.com/research/advisories/2003/a031303-2.txt


Overview:

      Nokia's (http://www.nokia.com) SGSN (Serving GPRS support
node) is the platform which exists between the legacy GSM network
and the new IP core of the GPRS network. This enables operators to
deploy high speed data access over the top of their GSM network with
minimal upgrades to their BSCs (Base Station Controllers), thus
making the transition from a 2.0G  to a 2.5G network.

Due to its position in the network (i.e. between the RF network and
the IP network) the SGSN will have interfaces on the SS7 signaling
network and the IP core network as well as  connections to the BSCs.
For this reason, the SGSN can be considered a key part of the
infrastructure of any mobile operator looking to deploy GPRS.

A vulnerability exists in the SNMP (Simple Network Management
Protocol) daemon of the DX200 based network element that allows an
attacker to read SNMP options with ANY community string.

This is a good example of why network elements which introduce IP
functionality to legacy networks should have their functionality
verified in terms of impact on security before deployment in a
production environment.


Proof of Concept:

      The following proof of concept will return the the default MIB
information on the DX200 based network element using the snmpwalk and
snmpset commands which ship by default with operating systems such
as Linux.

      [reading of SNMP details]
      snmpwalk <IP of SGSN> tellmeyoursecrets


Vendor Response:

      In SNMP v1 (RFC 1157) and v2c (RFC 1901) standards,
authentication is based on a community string (text string)
representing an unencrypted username without a password. A recognized
concern in industry is that the security check as documented in these
SNMP standards is inadequate.

Because of the above,  read access to MIB-II (RFC 1213)  variables is
allowed in Nokia SGSN SG1 / SG1.5 products with any community string
value. However, write access to MIB-II  variables is not permitted in
Nokia SGSN SG1 / SG1.5 products, even though the SNMP MIB-II RFC
standard defines some of the MIB-II variables to be write accessible.
Nokia has made a product design decision that the value of each write
accessible MIB-II variable remains unchanged, even in cases where the
SNMP agent in Nokia SGSN SG1 / SG1.5 products would return an OK
status notification as a response to the SNMP set-request operation.

This means that a malicious attacker is under no circumstances able
to alter any settings of Nokia SGSN SG1 / SG1.5 products via the SNMP
interface. Furthermore, support for the SNMP interface has been
removed from subsequent Nokia SGSN releases, which eliminates the
possibilities for SNMP based vulnerabilities completely.


Vendor Recommendation:

      Network operators do not need to take any further action.


@stake Recommendation:

      Typically in a GPRS network design, the SGSN should not be
contactable from the Gi interface of the GGSN where the user's
routable IP is located. This is due to the fact that GGSN to SGSN
communication occurs over the Gn interface. However @stake has
observed instances where the NMS (Network Management System) network
is routable from the Gi network. If the SGSN has an NMS connection,
then appropriate ACLs (Access Control Lists) should be deployed on
the routing device or firewall between the Gi and the NMS networks to
restrict access to SNMP.


Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned
the following names to these issues.  These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

 CVE Candidate number applied for


@stake Vulnerability Reporting Policy:
http://www.atstake.com/research/policy/

@stake Advisory Archive:
http://www.atstake.com/research/advisories/

PGP Key:
http://www.atstake.com/research/pgp_key.asc


@stake is currently seeking application security experts to fill
several consulting positions.  Applicants should have strong
application development skills and be able to perform application
security design reviews, code reviews, and application penetration
testing. Please send resumes to jobs () atstake com
Copyright 2003 @stake, Inc. All rights reserved.


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