Thursday, December 29, 2011

Run a ASP.Net site/service? Update now... (Vulnerability in ASP.NET Could Allow Denial of Service and Vulnerabilities in .NET Framework Could Allow Elevation of Privilege)

Scott Gu - ASP.NET Security Update Shipping Thursday, Dec 29th

"A few minutes ago Microsoft released an advance notification security bulletin announcing that we are releasing an out-of-band security update to address an ASP.NET Security Vulnerability.

The security update we are releasing resolves a publicly disclosed Denial of Service issue present in all versions of ASP.NET. We’re currently unaware of any attacks on ASP.NET customers using this exploit, but we strongly encourage customers to deploy the update as soon as possible.

We are releasing the security update via Windows Update and the Windows Server Update Service. You can also manually download and install it via the Microsoft Download Center. We will release the update on Thursday, December 29th at approximately 10am Pacific Time (US and Canada). We are announcing it ahead of time to ensure that administrators know that the security update is coming, and are prepared to apply it once it is available.


Security Research & Defense - More information about the December 2011 ASP.Net vulnerability

Today, we released Security Advisory 2659883 alerting customers to a newly disclosed denial-of-service vulnerability affecting several vendors’ web application platforms, including Microsoft’s ASP.NET. This blog post will cover the following:

  • Impact of the vulnerability
  • How to know if your configuration is vulnerable to denial-of-service
  • How to detect the vulnerability being exploited at network layer
  • How to detect the vulnerability being exploited on the server
  • Background on the workaround to protect your website

Impact of the vulnerability

This vulnerability could allow an anonymous attacker to efficiently consume all CPU resources on a web server, or even on a cluster of web servers. For ASP.NET in particular, a single specially crafted ~100kb HTTP request can consume 100% of one CPU core for between 90 – 110 seconds. An attacker could potentially repeatedly issue such requests, causing performance to degrade significantly enough to cause a denial of service condition for even multi-core servers or clusters of servers.

We anticipate the imminent public release of exploit code. Therefore, we encourage ASP.NET website owners to review the Security Advisory 2659883 and this blog post to evaluate the denial-of-service risk to your web property and to implement the workaround and/or attack detection mechanisms until a security update is available to comprehensively address the issue.

Vulnerable configurations

The root cause of the vulnerability is a computationally expensive hash table insertion mechanism triggered by an HTTP request containing thousands and thousands of form values. Therefore, any ASP.NET website that accepts requests having HTTP content types application/x-www-form-urlencoded or multipart/form-data are likely to be vulnerable. This includes the default configuration of IIS when ASP.NET is enabled and also the majority of real-world ASP.NET websites.

Detecting attacks at the network layer


Security Bulletins - Microsoft Security Bulletin MS11-100 - Critical

Vulnerabilities in .NET Framework Could Allow Elevation of Privilege (2638420)

Executive Summary

This security update resolves one publicly disclosed vulnerability and three privately reported vulnerabilities in Microsoft .NET Framework. The most severe of these vulnerabilities could allow elevation of privilege if an unauthenticated attacker sends a specially crafted web request to the target site. An attacker who successfully exploited this vulnerability could take any action in the context of an existing account on the ASP.NET site, including executing arbitrary commands. In order to exploit this vulnerability, an attacker must be able to register an account on the ASP.NET site, and must know an existing user name.

This security update is rated Critical for Microsoft .NET Framework 1.1 Service Pack 1, Microsoft .NET Framework 2.0 Service Pack 2, Microsoft .NET Framework 3.5 Service Pack 1, Microsoft .NET Framework 3.5.1, and Microsoft .NET Framework 4 on all supported editions of Microsoft Windows. [GD: Emphasis added] For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerabilities by correcting how the .NET Framework handles specially crafted requests, and how the ASP.NET Framework authenticates users and handles cached content. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

This security update also addresses the vulnerability first described in Microsoft Security Advisory 2659883.

Recommendation. The majority of customers have automatic updating enabled and will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers consider applying the security update using update management software, or by checking for updates using the Microsoft Update service.


Why does it seem these always happen during the holiday's? Sigh...

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