"An 'Asp.Net' accident waiting to happen" - Draft article


D

Dinis Cruz

Hello

Please see bellow the final draft of an article soon to be published.

I would appreciate your comments and corrections of anything that I
might have got wrong.

Best regards

Dinis Cruz


-------------------------------------


An 'Asp.Net' accident waiting to happen

I would like to call the attention of the Asp.Net Community and
Microsoft to an accident waiting to happen. In a time where Security
is finally being taken seriously by Microsoft, their focus is still in
adding features to products and not making the existent products
secure.

The accident will be the wide spread exploitation of websites hosted
in shared hosting environments (such as ISPs). The problems described
next will also affect any major Asp.Net application, but their
problems will be dealt privately and lessons will not be learnt by the
community.

Asp.Net is the latest and most powerful web application development
tool produced by Microsoft. Although it is a major technological
advance from its predecessors (Asp, ISAPI, Web Classes, Custom COM
Objects developed in Visual Studio 6, etc.) it is also very dangerous.

The .Net framework (which is fully implemented in Asp.Net) is very
feature rich and powerful. It provides the developer (i.e. development
team) with a huge array of tools, objects and methods that make their
web application development a quick, easy and effective process.

Microsoft, knowing that security is becoming more and more a central
issue for end clients, included in the .Net framework several
technologies that allow the creation and deployment of secure
applications. The most important are:

- Code Access Security (CAS)
- Ability to deploy APTCA (AllowPartiallyTrustedCallersAttribute)
assemblies in the GAC (Global Assembly Cache)
- Built in Encryption technology (DPAPI)
- Several methods to implement Secured Database Accesses
- Several authentication methods and Build-in Impersonation features
- Extended used of Role Based Security (used in conjunction with
Windows server security features)

IIS 6 web server and windows 2003 also provide some tools to deploy
secure websites:

- Applications pools (allow the execution of each website under the
rights on a unique (low privileged) user)
- Better management of process and threads

These tools should allow the developer to create secure applications
that could be deployed in secure servers.

The problem is that today, the development and deployment of secure
web applications in secure web servers is almost impossible because:

- Although CAS (Code Access Security) could be used to limit what a
web application could 'do' on the host server, in the real world it
doesn't work. Any web application that is executed in 'Partially
trusted' environments (i.e. not in 'Full Trust') will not have access
to fundamental Asp.Net features such as: Database connectivity using
OleDB or ODBC, use of COM objects and many other important features.

- If a developer wants to use the powerful Asp.Net development
environment in a quick, easy and effective way, the solution is to run
its Asp.Net code in 'Full Trust' environments. The problem is that
most security tools and technologies previously mentioned only work
effectively in 'Partially trusted' environments

- Most ISPs that provide Shared Hosting environments allow their
hosted websites to execute with 'Full Trust' rights. This means that
even if a developer manages to get their web application to work in
'Partially trusted' environments, he would not be able to find a
secure host for it. The only way around this is to purchase a
dedicated server, which is also very dangerous, because it would then
be the developer's responsibility to securely configure and manage it.

- Most developers will store sensitive information (such as usernames
and passwords) in an unencrypted format in configuration files stored
in their website's folders (for example in Web.config). This happens
because the current version of Asp.Net doesn't provide a quick,
effective and scalable solution to store encrypted data in the
registry (or other secure location)

- In a shared hosting environment everybody has access to everybody's
temporary files (i.e. the 'Asp.Net Temporary files' folder) and in
Asp.Net all code is initially compiled into IL (Intermediate Language)
which is easily decompiled into VB or C#. This means that every user
with access to a valid account in a shared hosting environment can
read the source code (.aspx, vb, cs or dll) of every website hosted in
that server.

- In 'Full Trust' environments, the developer has access to the entire
windows 32 API and (using reflection) all .Net functions (private or
public). This means that it is easy to write code that: Executes
commands on the server (i.e. creates processes), lists usernames,
lists running process, list installed services, open TCP connections,
etc...

Fundamentally, the problem is that the current version of the .Net
Framework (version 1.14) doesn't allow the creation of secure hosting
environments.

Unless (of course), one is prepared to developed 'Partially Trusted'
web applications.

This could be done by using the reduced (and very limited) 'Partially
Trusted' Asp.Net development environment, or by spending an extra 50%
to 100% development time in creating secure strong name assemblies
that can be published in the server's GAC (although this is not very
practical for ISPs).

Today (Oct/2003):

1) There are hundreds of ISPs providing 'Full Trust' Asp.Net shared
hosting services

2) Microsoft is not publicly acknowledging (as a problem or security
vulnerability) the fact that these ISPs have no alternative but to
provide 'Full Trust' shared hosting environments. And consequently is
not focused on providing or developing a solution.

3) Microsoft is focused in developing the next version of Asp.Net
(version 1.2) which will have even more features and will be even more
powerful (although Microsoft says that the new version will be more
secure)

4) Malicious users have already realized that the current windows
based ISP's hosting environments are insecure and easy to exploit.
Although most incidents are still private and the ISPs will not
publicly acknowledge their existence, recently one case was so serious
that it got some press attention: See the "Interland Security
Incident" story where a malicious user injected malicious code in
several websites hosted by Interland's shared hosting servers. This
code used known bugs in the website's visitors Internet Explorer Web
Browser which (description from the Wired article) "... Web surfers
who have visited the compromised sites might get a surprise on their
next phone bill when they discover expensive calls made to 900
numbers. Others could also find themselves party to a
denial-of-service attack launched against another computer...". For
more details read this article: "Wired.com : 'Security holes Vex Web
Hosting Firm' : http://www.wired.com/news/business/0,1367,60303,00.html"
and this "news.com : 'Web Hosting Company confirms hack attack' :
http://news.com.com/2100-1002-5076050.html" and this
"ComputerWorld.com : 'Security breach at Web host leaves sites at
risk' : http://www.computerworld.com/securitytopics/security/story/0,10801,84675,00.html".

5) The ISPs are telling their clients that their shared hosting
servers are secure and the clients believe them (reinforced by the
fact that Microsoft doesn't acknowledge the problem). This is quite
important because if the clients where aware of these problems, they
would demand (and possibly pay more for) secure environments to host
their websites.

The massive exploitation of these vulnerabilities by malicious users
is just a matter of time. In my view the most dangerous problem is the
fact that (today) there is no real alternative (i.e. solution) to
securely host Asp.Net websites in a shared hosting environment.

If in a near future a major security incident occurs (with widespread
media coverage) and, the ISPs had to (or where forced to) change the
current 'Full Trust' level to a 'Partially trusted' level, the side
effect would be that most (if not all) hosted Asp.Net websites would
stop working or would seriously malfunction.

In conclusion, it is an 'Asp.Net' accident waiting to happen!

Dinis Cruz is a Security Consultant currently working for several UK
governmental Departments, International Corporations and ISPs. He is
specialist in .Net Security and is the creator and main developer of
the Open Source web application ANSA (Asp.Net Security Consultant). He
is also the managing director of DDPlus; a UK based IT Security
Company (www.ddplus.net). Dinis can be contacted on (e-mail address removed)
 
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