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Barracuda Web Security Gateway

Why doesn't NTLM authentication to the Barracuda Web Filter work from a Windows Vista or Windows 7machine?

  • Type: Knowledgebase
  • Date changed: 3 years ago
Solution #00003944


Applies to all Barracuda Web Filters, all firmware versions.


When a user tries to access a web site, from a network using NTLM authentication, Windows Vista and Windows 7 fails to send the user?s password to the Barracuda Web Filter. This happens because Windows Vista/Windows 7 uses NTLMv2 challenge/response authentication and the Barracuda Web Filter is expecting NTLMv1. 


The solution is to force the Windows machine to use the older encryption method as follows:


Vista/7 Home Basic and Home Premium

  1. Go to Start > Run, to open a command prompt and then type regedit.
  2. Expand the folders for HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa.
  3. Double click to open and modify the LmCompatibilityLevel parameter.
  4. Type 1 in the Value Data field (replace the default value of 3).
  5. Click OK.

Windows Vista/7 Business, Enterprise, and Ultimate

  1. Go to Start > Control Panel > System and Maintenance > Administrative Tools > Local Security Policy.
  2. Click the triangle next to Local Policy > Security Options.
  3. Double click to open Network security: LAN Manager Authentication Level.
  4. Select Send LM & NTLM - Use NTLMv2 Session Security if Negotiated from the dropdown box.
  5. Click OK.


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