[NEWS] Cisco PIX Vulnerabilities (SNMP, VPNC)

From: SecuriTeam (support_at_securiteam.com)
Date: 12/18/03

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      Cisco PIX Vulnerabilities (SNMP, VPNC)
    ------------------------------------------------------------------------

    SUMMARY

    This advisory documents two vulnerabilities for the Cisco PIX firewall.
    These vulnerabilities are documented as CSCeb20276 (SNMPv3) and
    CSCec20244/CSCea28896 (VPNC)

    There are workarounds available to mitigate the effects of CSCeb20276
    (SNMPv3). No workaround is available for CSCec20244/CSCea28896 (VPNC).

    DETAILS

    Affected Products:
    All Cisco PIX firewall devices running the affected Cisco PIX firewall
    software, as documented below, are affected by these vulnerabilities.
     * CSCeb20276 (SNMPv3) 6.3.1, 6.2.2 and earlier, 6.1.4 and earlier. 5.x.x
    and earlier.
     * CSCec20244/CSCea28896 (VPNC) 6.2.3 and earlier. 6.1.x and 5.x.x are not
    affected; they do not implement the VPNC feature.

    The Firewall Service Module (FWSM) is also vulnerable to the SNMPv3 issue
    and is documented as
    <http://www.cisco.com/warp/public/707/cisco-sa-20031215-fwsm.shtml>
    http://www.cisco.com/warp/public/707/cisco-sa-20031215-fwsm.shtml. No
    other Cisco products are currently known to be affected by these
    vulnerabilities.

    To determine your software revision, type show version at the command line
    prompt.

    Details:
     * CSCeb20276 (SNMPv3)

    The Cisco PIX firewall crashes and reloads while processing a received
    SNMPv3 message when snmp-server host <if_name> <ip_addr> or snmp-server
    host <if_name> <ip_addr> poll is configured on the Cisco PIX firewall.
    This happens even though the Cisco PIX firewall does not support SNMPv3.

    A Cisco PIX firewall configured to only generate and send traps using the
    snmp-server host <if_name> <ip_addr> trap command is not vulnerable.

     * CSCec20244/CSCea28896 (VPNC)
    Under certain conditions, an established VPNC IPSec tunnel connection is
    dropped if another IPSec client attempts to initiate an IKE "Phase I"
    negotiation to the outside interface of the VPN Client configured Cisco
    PIX firewall.

    Only a Cisco PIX firewall configured as a VPN Client is vulnerable to this
    vulnerability.

    A VPNC also referred to as Easy VPN or ezVPN, connection is created when
    the Cisco PIX firewall is used as a VPN client to connect to a VPN server.
    An IKE Phase I negotiation is a step in the establishment of an IPSec
    session.

    CSCea28896 resolved this issue for the 6.3.x software releases and
    CSCec20244 resolved this issue for the 6.2(3.100) and later software
    releases.

    The Internetworking Terms and Cisco Systems Acronyms online guides can be
    found at <http://www.cisco.com/univercd/cc/td/doc/cisintwk/>
    http://www.cisco.com/univercd/cc/td/doc/cisintwk/.

    These vulnerabilities are documented in the Cisco Bug Toolkit as Bug ID
    CSCeb20276 (SNMPv3) and CSCec20244/CSCea28896 (VPNC). To access this tool,
    you must be a registered user and you must be logged in.

    Impact:
     * CSCeb20276 (SNMPv3)
    This vulnerability can be exploited to initiate a Denial of Service attack
    on the Cisco PIX firewall.

     * CSCec20244/CSCea28896 (VPNC)
    This vulnerability can be exploited to initiate a Denial of Service attack
    on sessions established between a Cisco PIX configured as a VPN Client and
    a VPN server.

    Software Versions and Fixes:
     * CSCeb20276 (SNMPv3) 6.3.2 and later, 6.2.3 and later, 6.1.5 and later.

     * CSCec20244/CSCea28896 (VPNC) 6.3.1 and later, 6.2(3.100) and later.

    The procedure to upgrade to the fixed software version is detailed at
    <http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/index.htm> http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/index.htm.

    Workarounds:
     * CSCeb20276 (SNMPv3)

    There are two workarounds available.
     o If SNMP polling to the PIX is required on a vulnerable image, one may
    choose to restrict the polling access to the SNMP server to trusted
    interfaces and trusted hosts by using this command:
       snmp-server host <if_name> <ip_addr> poll

    Note: Both Poll and Trap are enabled if one does not specifically use the
    poll or trap keyword in the command above. The above command cannot
    prevent a source IP spoofed SNMP request message from exploiting this
    vulnerability.

     o Disable the SNMP server on the Cisco PIX firewall as follows:
                clear snmp-server
                no snmp-server location
                no snmp-server contact
                snmp-server community public
                no snmp-server enable traps

    Note: The Cisco PIX firewall does not allow one to remove the community
    string altogether. It will always be either public or a user configured
    string. show snmp will still show snmp-server community public, but this
    does not mean SNMP is enabled.

    More details at
    <http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_62/cmdref/s.htm#1026423> http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_62/cmdref/s.htm#1026423.

     * CSCec20244/CSCea28896 (VPNC)

    No workaround. Please upgrade.

    The Cisco PSIRT recommends that affected users upgrade to a fixed software
    version of code.

    ADDITIONAL INFORMATION

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

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