Microsoft Security Bulletin MS99-047 - Critical
Patch Available for "Malformed Spooler Request" Vulnerability
Published: November 04, 1999
Originally Posted: November 04, 1999
Microsoft has released a patch that eliminates a security vulnerability in Microsoft® Windows NT® 4.0. The vulnerability could allow a user to cause the print spooler service to crash, or to run arbitrary code on a Windows NT machine. The patch also eliminates a vulnerability that could allow a user to substitute code of their choosing for a print provider that runs in a privileged state.
Frequently asked questions regarding this vulnerability can be found at
Certain APIs in the Windows NT 4.0 print spooler subsystem have unchecked buffers. If an affected API were provided with random data as input, it could crash the print spooler service. If it were provided with a specially-malformed argument, it could be used to run arbitrary code on the server via a classic buffer overrun attack. The majority of the affected APIs require the caller to be a member of the Power Users or Administrators group; however, at least one is callable by normal users. None of the calls could be made by anonymous users, but the calls could be made remotely.
A second vulnerability exists because incorrect permissions would allow a normal user to specify his or her own code as a print provider. Because print providers run in a local System context, this would allow the user to gain additional privileges on the local machine. This vulnerability could not be exploited remotely.
Affected Software Versions
- Microsoft Windows NT 4.0 Workstation
- Microsoft Windows NT 4.0 Server
- Microsoft Windows NT 4.0 Server, Enterprise Edition
- Microsoft Windows NT 4.0 Server, Terminal Server Edition
Windows NT 4.0 Workstation, Windows NT 4.0 Server and Windows NT 4.0 Server, Enterprise Edition:
Note The patches above can be installed on systems running Windows NT 4.0 Service Pack 5 or 6. A version that can be installed on systems running previous service packs will be released shortly.
Windows NT 4.0 Server, Terminal Server Edition:
- This vulnerability is eliminated in Service Pack 6 for Windows NT 4.0 Server, Terminal Server Edition.
Please see the following references for more information related to this issue.
Microsoft Security Bulletin MS99-047: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-047.mspx.
Microsoft Knowledge Base (KB) article 243649, Unchecked Print Spooler Buffer may Expose System Vulnerability, http://support.microsoft.com/default.aspx?scid=kb;en-us;243649&sd=tech Note It may take 24 hours from the original posting of this bulletin for this KB article to be visible.
Microsoft Security web site, http://www.microsoft.com/technet/security/default.mspx.
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at
Microsoft acknowledges the eEye Digital Security Team (http://www.eeye.com/html/) for discovering the buffer overrun vulnerability and reporting it to us.
- November 04, 1999: Bulletin Created.
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