MS-ISAC ADVISORY NUMBER:
2011-062

DATE(S) ISSUED:
10/11/11

SUBJECT:
Vulnerability in the Microsoft .NET Framework and Microsoft Silverlight Could Allow Remote Code Execution (MS11-078)

OVERVIEW:

A vulnerability has been discovered in the Microsoft .NET Framework and Microsoft Silverlight which could allow an attacker to take complete control of an affected system. Microsoft .NET is a software framework for applications designed to run under Microsoft Windows. Microsoft Silverlight is a web application framework that provides support for .NET applications and used for streaming media. This vulnerability can be exploited if a user visits or is redirected to a malicious web page, or runs a specially crafted Microsoft .NET or Silverlight application.

Successful exploitation could result in an attacker gaining the same privileges as the logged on user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

SYSTEMS AFFECTED:

  • Microsoft Silverlight 4
  • Microsoft .NET Framework 1.0 SP3
  • Microsoft .NET Framework 1.1 SP1
  • Microsoft .NET Framework 2.0
  • Microsoft .NET Framework 3.5.1
  • Microsoft .NET Framework 4.0

RISK:
Government:

  • Large and medium government entities: High
  • Small government entities: High

Businesses:

  • Large and medium business entities: High
  • Small business entities: High

Home users: High

DESCRIPTION:
A vulnerability has been discovered in the Microsoft .NET Framework and Microsoft Silverlight which could allow an attacker to take complete control of an affected system. The vulnerability in Microsoft .NETFramework and Microsoft Silverlight is due to the software not properly restrict inheritance within classes. This vulnerability can be exploited through the following attack scenarios:

In the first scenario, an attacker uploads malicious ASP.NET code to a web server that hosts user-created content. Successful exploitation could result in the attacker gaining the same privileges as the service account associated with the application pool identity. Depending on the privileges granted to the service account and on the application pool configuration, an attacker might be able to take control of other application pools on the Web server or be able to take complete control of the affected system.

In the second scenario, exploitation could occur if a user visits a specially crafted website that hosts malicious XBAP (Extensible Application Markup Language Browser Application) content. Successful exploitation could result in an attacker gaining the same privileges as the logged on user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

In the third scenario, an attacker can exploit this issue by creating Windows .NET applications tobypass Code Access Security (CAS) restrictions. Successful exploitation could result in an attacker gaining the same privileges as the logged on user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

RECOMMENDATIONS:
We recommend the following actions be taken:

  • Apply appropriate patches provided by Microsoft to vulnerable systems immediately after appropriate testing.
  • Remind users not to visit un-trusted websites or follow links provided by unknown or un-trusted sources.
  • Run all software as a non-privileged user (one without administrative privileges) to diminish the effects of a successful attack.
  • Apply the principle of Least Privilege to all services.
  • Unless there is a business need to do otherwise, consider disabling XAML browser applications in Internet Explorer.

REFERENCES:
Microsoft:
http://technet.microsoft.com/en-us/security/bulletin/ms11-078

CVE:
http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1253

Security Focus:
http://www.securityfocus.com/bid/49999