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Chunked encoding post can consume excessive memory on IIS 4.0 webserver

Vulnerability Note VU#25716

Original Release Date: 2002-06-13 | Last Revised: 2002-06-13


Microsoft IIS 4.0, circa March 2000, contained a vulnerability that allowed an intruder to consume unlimited memory on a vulnerable server.


Older versions of IIS 4.0, circa March 2000, contained a vulnerability in the chunked-encoding transfer mechanism that permitted an intruder to allocate unlimited memory on the server. Quoting from Microsoft security bulletin MS00-018:

IIS 4.0 supports chunked encoding transfers, but does not limit the size of the buffer that can be reserved. This would allow a malicious user to request an extremely large buffer for a POST or PUT operation, but never actually send data, thereby blocking memory on the server that had been allocated to the session.

This would not permit an intruder to execute code.


Intruders can interrupt the ordinary operation of a vulnerable IIS 4.0 server, potentially preventing it from responding to legitimate requests. Additionally, an intruder may be able to degrade the overall performance of other process on the machine.


Apply a patch as described in MS00-018.

Vendor Information

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Microsoft Corporation

Updated:  June 13, 2002



Vendor Statement


Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A



Thanks to Petteri Stenius for reporting this vulnerability.

This document was written by Shawn V Hernan based on information provided by Microsoft in MS00-018

Other Information

CVE IDs: CVE-2000-0226
Severity Metric: 2.62
Date Public: 2000-03-20
Date First Published: 2002-06-13
Date Last Updated: 2002-06-13 18:42 UTC
Document Revision: 3

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