Microsoft is investigating a reported vulnerability in
its ASP.NET that could allow an attacker to bypass security
features on a web server and view sensitive content.
The company published an advisory for website administrators on
the vulnerability on Tuesday 5 October and provided instructions
for mitigating the effects of the hole, which is in a component of
ASP.NET called the "canonicalisation routine".
Attackers could create URLs that are specially designed to
exploit the flaw, enabling them to bypass authentication or Windows
authorisation on web applications that use ASP.NET, Microsoft
said.
ASP.NET is the latest version of Microsoft's Active Server Page
(ASP) technology, which allows developers to create web-based
applications by embedding small programs, written in a variety of
languages such as Visual Basic, Perl and C#, in web pages, which
are then transmitted to users.
The canonicalisation routine is a process that interprets URL
requests for content on a web server and determines the proper way
to respond for those requests.
For example, there is more than one way to refer to the location
of a file, such as homepage.html, on a web server. The
canonicalisation routine interprets the information in a URL to
determine what page the URL is asking for, according to information
on the Microsoft web page.
The vulnerability affects all versions of ASP.NET, including
versions running on Windows 2000, Windows 2000 Server, XP
Professional and Windows Server 2003, Microsoft said.
Microsoft has released a small software module called the
Microsoft ASP.NET ValidatePath module (VPModule.msi) that can be
applied to Internet Information Server 5.0, 5.1 or 6.0 web servers
and will prevent exploitation of the ASP.NET vulnerability. The
company is also working on a security patch for the vulnerability,
it said.
The company also recommended that website owners review its
knowledge base for suggestions on ways to programme checks for
problems with URL canonicalisation.
Paul Roberts writes for IDG News Service