How to prevent DNS cache pollution

DNS cache pollution can occur if Domain Name System (DNS) "spoofing" has been encountered. The term "spoofing" describes the sending of non-secure data in response to a DNS query. It can be used to redirect queries to a rogue DNS server and can be malicious in nature.

Note If a DNS server has been configured to forward resolution requests to another server, establishing a child-parent relationship, the child DNS server could still be vulnerable to DNS cache pollution attacks performed against a parent DNS server if that server is not performing DNS cache pollution protection. By default, Microsoft DNS servers, using Windows 2000 Service Pack 3 or later, acting as a parent in a child-parent relationship will fully perform cache pollution protection. Therefore, make sure that all DNS servers in an organization have DNS cache pollution protection enabled.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

Windows NT 4.0

With Windows NT 4.0 Service Pack 4 (SP4) or later, a Windows NT-based DNS server can filter out the responses for these non-secure records.

To enable this feature:

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DNS\Parameters
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value Name: SecureResponses
   Data Type: REG_DWORD
   Value: 1 (To eliminate non-secure data)
4. Quit Registry Editor.

By default, this key does not exist and non-secure data is not eliminated from responses.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

Windows 2000

A Windows 2000-based DNS server can filter out the responses for these non-secure records.

To enable this feature:

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DNS\Parameters
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value Name: SecureResponses
   Data Type: REG_DWORD
   Value: 1 (To eliminate non-secure data)
4. Quit Registry Editor.

By default, on Windows 2000 Service Pack 1 (SP1) and Windows 2000 Service Pack 2 (SP2), this key does not exist and non-secure data is not eliminated from responses. Although DNS cache pollution protection is enabled by default in Windows 2000 SP3 and later, the registry key does not exist and is not needed. The only reason to create this registry key is to disable DNS cache pollution protection. For more information about DNS cache pollution protection, click the following article number to view the article in the Microsoft Knowledge Base:

Note On Windows 2000, you can perform the same entry in the GUI. Use the following steps to do this:

1. Open the DNS Management Console by clicking Start, Programs, Adminstrative Tools, and then clickingDNS.
2. Right-click on the server name in the left window pane.
3. Choose Properties.
4. Choose the Advanced tab.
5. Place a check in the box "Secure cache against pollution".

Windows 2003

DNS cache pollution protection is enabled by default in Microsoft Windows 2003.

To view the DNS cache pollution settings, use the following steps:

1. Open the DNS Management Console by clicking Start, Programs, Adminstrative Tools, and then clicking DNS.
2. Right click on the server name in the left window pane.
3. Choose Properties.
4. Choose the Advanced tab.
5. Confirm that the "Secure cache against pollution" check box is selected.

Note In Windows 2003 DNS, the registry key setting does not exist, however the setting is enabled in the GUI by default. You can also check the current setting by running the following command at a command prompt: Dnscmd /Info /SecureResponses