[NT] Citrix Metaframe Presentation Server Policies Bypassing

From: SecuriTeam (support_at_securiteam.com)
Date: 10/06/05

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      Citrix Metaframe Presentation Server Policies Bypassing
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.citrix.com/> Citrix Presentation Server - "is the world s
    most widely deployed presentation server for centrally deploying and
    managing applications, especially in a heterogeneous environment, and
    delivering their functionality as a service to workers, wherever they may
    be."

    A vulnerability in Presentation Server allows a user bypass Citrix
    policies that have been applied to client name.

    DETAILS

    Vulnerable Systems:
     * Citrix Metaframe Presentation Server versions 3.0 and 4.0

    Citrix Presentation Server policy is used for administrators to restrict
    the user environment and these allow applying to: IP client, servers,
    Users, o Client Name.

    When user used the Web Interface to access to application in Citrix
    environment the CLIENT NAME used is WI_*, where (*) is a random value like
     asdfserw34vc342dk this extension allow administrators to use Citrix
    policy based in client name "WI_*" This policy can be used to restrict
    "printing Mapping, Disk Mapping, Control bandwidth, manage printer driver
    environment so..."

    When user uses the application in Web interface, he download and execute
    automatic file "launch.ica".
    If the user "save as" launch.ica in his PC, and edit with notepad. He can
    change the value in ClientName that another "WI_" and execute.

    When user connects to Citrix with ica file modified to Presentation
    Server, the value in clientname is different to the original one and
    bypasses the Citrix policies.

    Proof of concept:
    Here is an example extracted from launch.ica:

     [Encoding]
     InputEncoding=ISO8859_1
     [WFClient]
     Version=2
     ClientName=WI_XXXX -> change this extension with other name to bypass the
    citrix policies
     TransportReconnectEnabled=On
     RemoveICAFile=yes
     ProxyType=None
     ProxyTimeout=30000

    Vendor Status:
     
    <http://support.citrix.com/kb/entry!default.jspa?categoryID=275&externalID=CTX107705> http://support.citrix.com/kb/entry!default.jspa?categoryID=275&externalID=CTX107705

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:gustavog@grupoiptro.com.ar>
    Gustavo Gurmandi.
    The original article can be found at:
    <http://www.grupoitpro.com.ar/ctxpoliciesbypass.txt>
    http://www.grupoitpro.com.ar/ctxpoliciesbypass.txt

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