Home > Articles > Operating Systems, Server > Microsoft Servers

  • Print
  • + Share This

Client/Web Server Communications

There are really two distinct security issues between the user's Web browser and the Web server:

  • Clear-text transmission of the HTML text stream—In particular, the user credentials entered on the NFuse logon screen are passed as clear text back to the Web server.

  • Cached session information maintained on the user's personal computer—This includes user credentials stored in clear-text cookies and the ICA connection files, which can also contain user credential information that can possibly be exploited to gain access to a MetaFrame server.

Secure Sockets Layer and the HTML Text Stream

The most common way to secure the transmission of HTML text between a Web browser and the server is to use the Secure Sockets Layer (SSL) protocol. SSL provides support for server and client authentication, as well as data integrity and encryption. All Web servers and Web browsers that are compatible with NFuse 1.5 provide SSL support. To enable SSL connectivity, you will need to configure SSL on the NFuse-enabled Web server. For complete details on how to set up SSL connectivity for your particular Web server, refer to the server's documentation.

In my test environment, I am running IIS 5.0 on a Windows 2000 Server. To configure my IIS server to use SSL, I would go through the following steps:

  1. Acquire and install a server certificate on my Web server. This certificate verifies the identity of my Web server. Before SSL communications can be established, the Web browser must be capable of successfully matching this certificate against its list of trusted certificate authorities (CA). For my example, I am going to use a Web server certificate issued by a Microsoft Certificate Authority that is internal to my company (Noisy River). Certificates are installed and configured in IIS 5 by opening the IIS management snap-in and selecting the Properties option for your Web server. Figure 2 shows my sample IIS Web site along with the corresponding properties page. Under the Directory Security tab you will see a Server Certificate button. Until a valid certificate has been installed, the View and Edit buttons will not be available.

  2. Figure 2

    IIS 5.0 Web site property page

  3. After the certificate has been installed, the next step is to configure the Web site to require SSL encryption. I simply right-click on my Web folder, select Properties, and then click Edit under the Directory Security tab. Here there is a Require Secure Channel checkbox and a Require 128-Bit Encryption checkbox, as shown in Figure 3. Once selected, an SSL secure channel is required for a user to access the Web page.

  4. Figure 3

    Configuring a Web page to use a secure SSL channel

When these steps are completed, an intranet user in my company should be able to connect to my site and automatically establish an SSL secure tunnel. Because a CA internal to Noisy River issued my server certificate, the first time that a user's Web browser attempts to access the NFuse site, a dialog box will appear similar to the one in Figure 4. This warns the user that while the server certificate is valid, it has not come from a CA that the browser has been configured to trust. Both Netscape and IE will provide the user with the option to trust certificates from this authority.

Figure 4

Unknown CA security alert in IE

Once accepted, the NFuse logon screen should appear, and the closed padlock icon should appear at the bottom of the Web browser (Netscape or IE). HTTP communications between the NFuse-enabled Web server and the user's Web browser are now secure.

Web Browser Cookies

Any of the generated NFuse Web sites created by the Web Site Wizard will store the user credentials in clear text within a cookie on the user's local desktop. By default, this cookie exists only for the duration of the user's session. Although SSL will protect the transmission of this cookie information, there is still the potential for someone with access to the user's local browser to retrieve this clear-text information. Citrix provides two possible "solutions" to this problem:

  • Encrypt the data before writing it to the cookie. Citrix includes an ASP sample Web site that performs this operation. It can be found in the NFuse15\ASPEncrypt folder in the root of your NFuse Web server. The actual encryption algorithm is a simple XOR of the password to be encrypted with a randomly generated 512-byte session key. The resulting encrypted password has the same length as the original password, but the text now appears scrambled. The generated encryption session key is maintained in a server-side session object. The Web pages associated with the ASPEncrypt example include a large amount of information that describes exactly what operations are being performed.

  • Instead of maintaining the user credentials in a cookie, they can be stored in session variables on the Web server. This session information is unique to each user that is connected to the Web server. For example, the following ASP text would store the user ID and domain information in the session object:

      Session("nfuseUserID") = user
      Session("nfuseDomain") = domain

    For complete information on session variables and their properties, consult an ASP or JSP (JavaServer Pages) reference.

Cached ICA Files and ICA Session Tickets

When a user clicks on an application link, the corresponding ICA file is downloaded and processed by the user's ICA client to establish the actual connection to the appropriate MetaFrame server. Typically this file is stored in the browser's local file cache and, as a result, can be a potential target for an attacker trying to gain access to the MetaFrame environment.

The real vulnerability lies not in the fact that by default the ICA file includes the user ID (in clear text), domain (also in clear text), and password (encrypted with Citrix's Basic encryption scheme), but that any ICA client can use this file to automatically log onto any MetaFrame server that the user has access to. If an attacker is capable of stealing an ICA file, then as long as the user does not change his password, that file can be used over and over again to launch the application with the user's credentials. The file could quite easily be edited to allow the attacker to establish a full desktop session on a MetaFrame server unless the appropriate security existed on the server to limit the user to a specific published application.

The follow is a sample ICA file that I copied from the Temporary Internet Files directory on a Windows 98 desktop that had been used to access a published application via an NFuse-enabled Web server.

[WFClient]
Version=2
ClientName=nrsc-joeuser

[ApplicationServers]
MS PowerPoint 2000=

[MS PowerPoint 2000]
Address=10.25.125.85
InitialProgram=#MS PowerPoint 2000
DesiredColor=2
TransportDriver=TCP/IP
WinStationDriver=ICA 3.0

Username=joeuser
Domain=nrsc
Password=0009a89b5289528d4a905c

DesiredHRES=640
DesiredVRES=480
TWIMode=On

[EncRC5-0]
DriverNameWin32=pdc0n.dll
[EncRC5-40]
DriverNameWin32=pdc40n.dll
[EncRC5-56]
DriverNameWin32=pdc56n.dll
[EncRC5-128]

DriverNameWin32=pdc128n.dll

Once I have this file, the first thing I can do is comment out the InitialProgram and TWIMode lines. The first change tells the ICA client to try to launch a full desktop instead of the specific published application, while the second change turns off the seamless windows mode. Unless connections on the MetaFrame server (10.25.125.85) have been limited to allowing only published application connections then these changes will allow me to run a full desktop session as joeuser.

Fortunately, the MetaFrame administrator has a few options available at her disposal to try to make the actual ICA file more secure:

  • Completely remove user credentials from the template.ica file

  • Use Citrix session tickets for user authentication instead of the standard user ID, domain, and password triplet

Removing User Credentials from the template.ica file

If you go in and modify the template.ica file for your Web site, you can completely remove any reference to the user's logon credentials. Without these credentials, the ICA file will not provide any additional information that could be used to compromise a user's account. The downside to this is that your users will be prompted to log onto every MetaFrame server that they connect to before being able to run the published application. To remove the stored credentials delete the following lines from the template.ica file:

<[NFuse_IFSESSIONFIELD sessionfield="NFUSE_ENCRYPTIONLEVEL" value="basic"]>
Username=[NFuse_User]
Domain=[NFuse_Domain]
Password=[NFuse_PasswordScrambled]
<[/NFuse_IFSESSIONFIELD]>

Implementing Session Ticketing

With the release of NFuse 1.5, Citrix has included a new user authentication security mechanism known as session ticketing. Session ticketing replaces the traditional process of passing the user ID, password, and domain to a MetaFrame server for logon. Instead, a session ticket is requested from the Citrix server farm by the Web server for the user before sending the ICA file. This session ticket information is placed into the ICA file, where it is then used by the client to perform user authentication. By default, session tickets are configured to have a timeout period of 200 seconds. After this time, or after the ticket has been used to authenticate the user, it expires and is no longer valid.

To use session tickets, you must have Service Pack 2 installed and Feature Release 1 activated on all servers that will be publishing applications. This is because FR1 includes updates to the MetaFrame server so that it can process session ticket logons properly. Nothing will happen if a user attempts to launch an application using a session ticket against a MetaFrame server that does not have FR1 activated. Session tickets are currently not supported with the initial release of the XML Service for Unix.

You can specify that you want to use ticketing during the generation of a Web site using the Web Site Wizard, or you can modify an existing site to use tickets simply by replacing the following user credential information in your template.ica file

<[NFuse_IFSESSIONFIELD sessionfield="NFUSE_ENCRYPTIONLEVEL" value="basic"]>
Username=[NFuse_User]
Domain=[NFuse_Domain]
Password=[NFuse_PasswordScrambled]
<[/NFuse_IFSESSIONFIELD]>

with the following two lines:

AutoLogonAllows=ON

[NFuse_Ticket]

The AutoLogonAllow option is used so that the ticket information is passed through if an encryption level higher than Basic is required to connect to the MetaFrame server. By default, autologon is not supported for any ICA session that is using security greater than Basic. This is because the user credential information is passed during an autologon before the actual establishment of a strong encryption session between the client and the server. I will talk more about ICA session encryption a little later in this article.

If I once again look at the cached ICA file (assuming that I have not turned off caching), I will see the following information instead of the regular user authentication data:

AutologonAllowed=ON
Username=joeuser
Domain=\6D4F78F34C1FC0D6

ClearPassword=E515275B5A8E8B

The backslash (\) character signals to the MetaFrame server that the standard user credentials have not been provided. Instead, a session ticket is to be used. The ticket is extracted and used to retrieve the domain and password information that is then used to log on the user. If someone attempts to use a ticket that has either expired or already been used, then the standard message displayed when an invalid password or user ID has been provided will appear. Essentially, the ICA file itself is useless, and a new one will need to be retrieved to allow the user to log onto either the same or a different MetaFrame server.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020