Webclass Sample

DOCUMENT:Q253155 11-JAN-2001 [vbwin] TITLE :HOWTO: Review Visual Basic WebClasses for CSSI Vulnerability PRODUCT :Microsoft Visual Basic for Windows PROD/VER:WINDOWS:6.0 OPER/SYS: KEYWORDS:kbVBp kbVBp600 kbDSupport ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning Edition for Windows, version 6.0 - Microsoft Visual Basic Professional Edition for Windows, version 6.0 - Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 ------------------------------------------------------------------------------- SUMMARY ======= This article describes how to identify and correct Visual Basic WebClass (IIS Applications) that are susceptible to cross-site scripting security issues (CSSI). Only input that is not correctly validated or formatted makes your application vulnerable to attack. This article focuses on Visual Basic 6.0 Webclass functionality (for example, replacement tags). For general guidelines regarding Active Server Pages (ASP) code, please see the following article in the Microsoft Knowledge Base: Q253119 HOWTO: Review ASP Code for CSSI Vulnerability MORE INFORMATION ================ Visual Basic Webclass developers should follow the guidelines for ASP code. These include: - Set the CHARSET for the page through the use of either a tag or Response.Charset. - Use Server.HTMLEncode() to encode any output that is generated from user input. - Use Server.URLEncode() to encode any output that is generated from user input that is included as part of a URL. The following sample code is an example of how you can use Server.HTMLEncode() and Server.URLEncode() in a Visual Basic 6.0 Webclass application to protect against the cross-site scripting vulnerability. It contains an HTML template (with replacement tags) and the associated Webclass source code. User-generated output that is included in the page source is encoded through the use of Server.HTMLEncode(). User-generated output that is included in the URL is encoded though the use of Server.URLEncode(): Template1.htm Webclass Sample

Here is some user generated output:

Here is a URL that contains user generated output: Click here!

WebClass Code Option Explicit Option Compare Text Private Sub WebClass_Start() Set NextItem = Template1 End Sub Private Sub Template1_Respond() Template1.WriteTemplate End Sub Private Sub Template1_ProcessTag(ByVal TagName As String, TagContents As String, SendTags As Boolean) Select Case TagName Case "WC@UserOutput" TagContents = Server.HTMLEncode("User Generated Output Here") Case "WC@URLFor" TagContents = URLFor(Template1) Case "WC@UserOutputURL" TagContents = Server.URLEncode("User Generated Output for URL Here") End Select End Sub REFERENCES ========== For more information, see the following advisory from the Computer Emergency Response Team (CERT) at Carnegie Mellon University: CERT(r) Advisory CA-2000-02 Malicious HTML Tags Embedded in Client Web Requests (http://www.cert.org/advisories/CA-2000-02.html) For additional information, click the article numbers below to view the articles in the Microsoft Knowledge Base: Q252985 HOWTO: Prevent Cross-Site Scripting Security Issues Q253119 HOWTO: Review ASP Code for CSSI Vulnerability Q253121 HOWTO: Review MTS/ASP Code for CSSI Vulnerability Q253120 HOWTO: Review Visual InterDev Generated Code for CSSI Vulnerability Q253117 Preventing Internet Explorer and Outlook Express Cross-Site Scripting Security Issues Additional query words: ====================================================================== Keywords : kbVBp kbVBp600 kbDSupport Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600 Version : WINDOWS:6.0 Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.