PR08-20: Bypassing ASP .NET "ValidateRequest" for Script Injection- Attacks

From: ProCheckUp Research <research@procheckup.com>
To: bugtraq@securityfocus.com
Cc: WebAppSec <webappsec@securityfocus.com>,websecurity@webappsec.org
Subject: PR08-20: Bypassing ASP .NET "ValidateRequest" for Script Injection- Attacks
Date:


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The Microsoft .NET framework comes with a request validation feature,
configurable by the ValidateRequest setting. ValidateRequest has been a
feature of ASP.NET since version 1.1. This feature consists of a series
of filters, designed to prevent classic web input validation attacks
such as HTML injection and XSS (Cross-site Scripting). This paper
introduces script injection payloads that bypass ASP .NET web validation
filters and also details the trial-and-error procedure that was followed
to reverse-engineer such filters by analyzing .NET debug errors.

The original version of this paper was released in January 2006 for
private CPNI distribution. This paper has now been updated in August
2008 to include additional materials such as input payloads that bypass
the latest anti-XSS .NET patches (MS07-40) released in July 2007.

Paper:

http://www.procheckup.com/PDFs/bypassing-dot-NET-ValidateRequest.pdf


Advisory:

http://www.procheckup.com/Vulnerability_PR08-20.php
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