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ScriptScan improvement to whitelist URLs for trusted web sites (Performance improvement for web-based applications that are script intensive)
Technical Articles ID:  KB65382
Last Modified:  06/21/2013
Rated:


Environment

McAfee VirusScan Enterprise 8.8
McAfee VirusScan Enterprise 8.7i Patch 1 and later

 

Summary

When VirusScan Enterprise (VSE) is installed with the ScriptScan component, it inserts a proxy between the incoming script and the Windows scripting host. This can cause poor performance with web pages and web-based applications that are script-intensive. It is now possible to whitelist URLs for trusted web sites, such as sites within an intranet or sites that you use frequently and know to be safe.

This functionality is available in:
  • VSE 8.8
  • VSE 8.7i with Patch 1 and later
NOTES: 
  • Do not use wild card characters.
  • Partial URLs can be used. Be cautious when specifying partial matches to avoid excluding scripts from unexpected web sites. For example, adding only www as would exclude scripts from any source that contains the characters www in the URL.
  • You must enable Browser Helper Objects
  • McAfee suggests that you use only Fully Qualified Domain Names and NetBIOS names.

    Examples:

    Internal URL
    To exclude the script named script.js from http://internal.something.local/scripts/script.js, the URL exclusion would be internal.something.local.

    External URL
    Excluding an external URL such as http://www.mcafee.com would be www.mcafee.com.

     
  • If your DNS server records contain CNAME entries for a particular URL, exclude them. 
  • Web pages can run scripts hosted on other sites or locations. If you require access to a script hosted on another site, you must also exclude the URL of the host site.
  • Do not include port numbers in exclusions. If a port number is specified, the exclusion will be ignored as invalid.


IMPORTANT:

Although it is possible to disable ScriptScan, McAfee recommends that you first create and test exclusions before you completely disable this feature. There is some security risk in disabling ScriptScan because applications like Outlook and Internet Explorer can render and execute scripts before a file has been created on the local system. It is important to point out that the On-Access scanner can stop the payload of attacks via this medium, but ScriptScan has the added advantage of preventing an actual threat from executing in the first place.

Customers can be confident that even though ScriptScan may not be right for all environments, VirusScan Enterprise 8.x provides superior protection against blended threats, with integrated Buffer Overflow protection for common desktop applications and services, Access Protection rules to block and contain common threat models, and true On-Access Scanning for malware, including Anti-Spyware, and rapid-response daily-DAT updates, backed by the power and performance of ePO.

McAfee recognizes, however, that this can potentially put customers in the difficult position of making the trade-off between enhanced protection and end-user performance. A customer can elevate their protection level back to a comparable level by installing a Secure Web Gateway appliance just behind their externally-facing web-servers. This solution will provide the same protection as ScriptScan, but is directed only at the external web traffic, leaving the internal portal traffic unencumbered.
 

Solution

Perform the following steps to create a URL exclusion:

CAUTION: This article contains information about opening or modifying the registry.
  • The following information is intended for System Administrators. Registry modifications are irreversible and could cause system failure if done incorrectly.
  • Before proceeding, McAfee strongly recommends backing up your registry and understanding the restore process. For more information, see: http://support.microsoft.com/kb/256986.
  • Do not run a .REG file that is not confirmed to be a genuine registry import file.


IMPORTANT: With the release of VSE 8.8 and later, the following changes can be carried out via an ePO VSE 8.8 policy, or through the local console if not managed by ePO.

  1. Click Start, Run, type regedit and click OK.
  2. Navigate to and select the appropriate registry key:

    • VSE 8.8: [HKEY_LOCAL_MACHINE\SOFTWARE\McAfee\SystemCore\VSCORE\Script Scanner]
    • VSE 8.7i: [HKEY_LOCAL_MACHINE\SOFTWARE\McAfee\VSCORE\Script Scanner]
        
  3. Click Edit, New, Multi-String Value, and name the new value ExcludedURLs.
  4. Add the URL to exclude. 
  5. Ensure that each URL or partial URL is separated by a carriage return.

    NOTE:
    This only works for Windows XP and later because you cannot create multi-string values (REG_MULTI_SZ) in Windows 2000. If necessary, multi-string values can still be imported into Windows 2000. 
     
  6. Close the registry editor.
  7. Close and restart all Internet Explorer windows to allow the new configuration to be read.

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