Microsoft KB Archive/169461

= Access Violation in Dns.exe Caused by Malicious Telnet Attack =

Article ID: 169461

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Server 4.0, Terminal Server Edition
 * Microsoft Windows NT Server 4.0 Standard Edition

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This article was previously published under Q169461





SYMPTOMS
You may receive an Access Violation in Dns.exe. This is most often occurs on computers connected to public networks, such as the Internet, where deliberate attacks are common.



CAUSE
This particular attack is usually generated maliciously by typing the following command on the attacking system:

telnet 19 | telnet 53

This command causes a telnet connection to be established to port 19 (the chargen service, which generates a string of characters) with the output redirected to a telnet connection to port 53 (the DNS service.) This flood of characters causes an Access Violation in the DNS service, which is terminated, disrupting name resolution services.



RESOLUTION
The Microsoft DNS Server has been modified to correct this problem.

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For your convenience, the English version of this post-SP3 hotfix has been posted to the following Internet location. However, Microsoft recommends that you install Windows NT 4.0 Service Pack 4 to correct this problem.

ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP3/dns-fix



MORE INFORMATION
For additional information, please see the following article(s) in the Microsoft Knowledge Base:

162927 Telnetting to Port 53 May Crash DNS Service



STATUS
Microsoft has confirmed this problem could result in some degree of security vulnerability in Windows NT version 4.0. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.

Additional query words: 4.00 denial of service dns telnet port 53

Keywords: kbbug kbfix kbnetwork KB169461

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