[VulnWatch] Nokia SGSN (DX200 Based Network Element) SNMP issue

From: @stake Advisories (@stake)
Date: 03/13/03

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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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