[NEWS] Vulnerability in Cisco IOS Embedded Call Processing Solutions

From: SecuriTeam (support_at_securiteam.com)
Date: 01/23/05

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      Vulnerability in Cisco IOS Embedded Call Processing Solutions
    ------------------------------------------------------------------------

    SUMMARY

    Cisco Internetwork Operating System (IOS ) Software release trains 12.1YD,
    12.2T, 12.3 and 12.3T, when configured for the Cisco IOS Telephony Service
    (ITS), Cisco CallManager Express (CME) or Survivable Remote Site Telephony
    (SRST) may contain a vulnerability in processing certain malformed control
    protocol messages.

    A successful exploitation of this vulnerability may cause a reload of the
    device and could be exploited repeatedly to produce a Denial of Service
    (DoS).

    Cisco has made free software upgrades available to address this
    vulnerability for all affected customers. There are workarounds available
    to mitigate the effects of the vulnerability.

    DETAILS

    Vulnerable Products
    This issue affects all Cisco devices running any unfixed version of Cisco
    IOS code that supports, and is configured for ITS, CME or SRST.

    A Cisco device running ITS or CME will have the following line in the
    configuration:
    telephony-service

    A Cisco device running SRST will have the following line in the
    configuration:
    call-manager-fallback

    To determine the software running on a Cisco product, log in to the device
    and issue the show version command to display the system banner. Cisco IOS
    Software will identify itself as "Internetwork Operating System Software"
    or simply "IOS." On the next line of output, the image name will be
    displayed between parentheses, followed by "Version" and the IOS release
    name. Other Cisco devices will not have the show version command or will
    give different output.

    The following example identifies a Cisco product running IOS release
    12.0(3) with an installed image name of C2500-IS-L:
    Cisco Internetwork Operating System Software IOS (TM)
    2500 Software (C2500-IS-L), Version 12.0(3), RELEASE SOFTWARE

    The release train label is "12.0".

    The next example shows a product running IOS release 12.3(6) with an image
    name of C2600-JS-MZ:
    Cisco Internetwork Operating System Software IOS (tm)
    C2600 Software (C2600-JS-MZ), Version 12.3(6), RELEASE SOFTWARE (fc1)

    Additional information about Cisco IOS release naming can be found at
    <http://www.cisco.com/warp/public/620/1.html>
    http://www.cisco.com/warp/public/620/1.html.

    Products Confirmed Not Vulnerable:
    ITS, CME and SRST are IOS-only features. Devices that do not run IOS are
    not vulnerable.

    Details:
    More information about Cisco's IOS Telephony Service (ITS) and Cisco
    CallManager Express (CME) can be found here:
    <http://www.cisco.com/en/US/products/sw/voicesw/ps4625/index.html>
    http://www.cisco.com/en/US/products/sw/voicesw/ps4625/index.html

    More information on Cisco's Survivable Remote Site Telephony (SRST) can be
    found here:
    <http://www.cisco.com/en/US/products/sw/voicesw/ps2169/index.html>
    http://www.cisco.com/en/US/products/sw/voicesw/ps2169/index.html

    ITS, CME and SRST are features that allow a Cisco device running IOS to
    control IP Phones using the Skinny Call Control Protocol (SCCP). SCCP is
    the Cisco CallManager native signaling protocol.

    Certain malformed packets sent to the SCCP port on an IOS device
    configured for ITS, CME or SRST may cause the target device to reload.
    This issue is documented in Cisco bug ID CSCee08584.

    The following commands can be used to determine if ITS or CME are running.
    A device that does not have ITS or CME enabled will display:
    Router#show telephony-service
    telephony-service is not enabled

    A device that has ITS or CME enabled will show something similar to:
    Router#show telephony-service
    CONFIG (Version=3.0)
     =====================
    Cisco CallManager Express
    ip source-address 192.168.1.1 port 2000
    max-ephones 2
    max-dn 2
    max-conferences 8
    max-redirect 5
    time-format 12
    date-format mm-dd-yy
    keepalive 30
    timeout interdigit 10
    timeout busy 10
    timeout ringing 180
    edit DN through Web: disabled.
    edit TIME through web: disabled.
    Log (table parameters):
         max-size: 150
         retain-timer: 15
    create cnf-files version-stamp Jan 01 2002 00:00:00
    auto assign 1 to 2
    local directory service: enabled.

    The following commands can be used to determine if SRST is running. A
    device that does not have SRST enabled will display:
    Router#show call-manager-fallback
    Call-manager fallback is not enabled

    A device that has SRST enabled will show something similar to:
    Router#show call-manager-fallback
    CONFIG
     ======
    ip source-address 192.168.1.1 port 2000
    max-ephones 2
    max-dn 4
    huntstop
    time-format 12
    date-format mm-dd-yy
    keepalive 30
    interdigit timeout 10
    busy timeout 10
    Limit number of DNs per phone:
      7910: 34
      7935: 34
      7940: 34
      7960: 34

    Spoofed attacks are impractical since the attacker must pass all of the
    TCP/IP integrity checks first, including the initial sequence number and
    source TCP port number.

    Impact:
    Successful exploitation of the vulnerability may result in a device
    reload. Repeated exploitation could result in a Denial of Service (DoS)
    attack.

    Software Versions and Fixes
    A list of vulnerable systems and their corresponding fixes can be found at
    the following link:
    <http://www.cisco.com/warp/public/707/cisco-sa-20050119-itscme.shtml#software> http://www.cisco.com/warp/public/707/cisco-sa-20050119-itscme.shtml#software

    Workarounds
    The effectiveness of any workaround is dependent on specific customer
    situations such as product mix, network topology, traffic behavior, and
    organizational mission. Due to the variety of affected products and
    releases, customers should consult with their service provider or support
    organization to ensure any applied workaround is the most appropriate for
    use in the intended network before it is deployed.

    Affected devices that must run ITS, CME or SRST are vulnerable, and there
    are not any specific configurations that can be used to protect them.
    Applying access lists on interfaces that should not accept ITS, CME or
    SRST traffic and putting firewalls in strategic locations may greatly
    reduce exposure until an upgrade can be performed.

    The IP Telephony Security in Depth SAFE paper at the URL below discusses a
    variety of best practices that should keep your voice network isolated
    from the Internet. These best practices may help to reduce the risk of
    exposure, although attacks from within the local network should always be
    considered a potential risk.
     
    <http://www.cisco.com/en/US/netsol/ns340/ns394/ns171/ns128/networking_solutions_white_paper09186a00801b7a50.shtml> SAFE: IP Telephony Security in Depth

    Using 'strict-match'
    It is possible to restrict SCCP communications to the IP specified in the
    ip source-address configuration command by using the strict-match option.
    More information on this command can be found at the following URL:

     
    <http://www.cisco.com/en/US/netsol/ns340/ns394/ns165/ns391/networking_solutions_design_guidance09186a00801f8e30.html#wp40333> Cisco CallManager Express Security Guide to Best Practices

    Using Access Lists
    Where possible, it is recommended to block SCCP traffic at the network
    edge with an Infrastructure Access Control List (iACL) or a Transit Access
    Control List (tACL).

    For more information on iACLs, refer to "Protecting Your Core:
    Infrastructure Protecton Access Control Lists":
    <http://www.cisco.com/warp/public/707/iacl.html>
    http://www.cisco.com/warp/public/707/iacl.html

    For more information on tACLs, refer to 'Transit Access Control Lists:
    Filtering at Your Edge": <http://www.cisco.com/warp/public/707/tacl.html>
    http://www.cisco.com/warp/public/707/tacl.html

    Below is an example of an access list to block SCCP traffic from anywhere
    but a permitted network.

    Note: In SRST deployments the SCCP packets are not addressed directly to
    the SRST device. The SCCP packets will be addressed to the call control
    devices (typically Cisco CallManager).

    In this example, the permitted telephony devices are on the 172.16.0.0/16
    network and the SCCP port being used is the default, TCP port 2000. If the
    specific IP addresses of the telephony devices are known, then the access
    list can be made to restrict traffic from only those devices.

    !--- Permit access from any IP address in the 172.16.0.0/16
    !--- to TCP port 2000.

    access-list 101 permit tcp 172.16.0.0 0.0.255.255 any eq 2000

    !--- Deny all traffic to port 2000.

    access-list 101 deny tcp any any eq 2000

    !--- Permit all other traffic.

    access-list 101 permit ip any any

    Using Control Plane Policing

    The Control Plane Policing (CoPP) feature may be used to mitigate this
    vulnerability. In the following example SCCP traffic is permitted to and
    from the 192.168.10.0/24 subnet. All other TCP port 2000 traffic destined
    to the device is blocked.
    access-list 140 deny tcp 192.168.10.0 0.0.0.255 any eq 2000
    access-list 140 deny tcp any 192.168.10.0 0.0.0.255 eq 2000
    access-list 140 permit tcp any any eq 2000
    access-list 140 deny ip any any

    class-map match-all sccp-class
      match access-group 140

    policy-map control-plane-policy
      class sccp-class

         police 8000 1500 1500 conform-action drop exceed-action drop

    control-plane
     service-policy input control-plane-policy

    CoPP is available in IOS release trains 12.2S and 12.3T. Additional
    information on the configuration and use of the CoPP feature can be found
    at the following URL:
    <http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/products_feature_guide09186a00801afad4.html> Control Plane Policing

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:psirt@cisco.com> Cisco
    Systems Product Security Incident Response Team.
    The original article can be found at:
    <http://www.cisco.com/warp/public/707/cisco-sa-20050119-itscme.shtml>
    http://www.cisco.com/warp/public/707/cisco-sa-20050119-itscme.shtml

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