C# Exceptions

Hi,

I'm testing a C# desktop application. During my testing so far we have
found security issues that lead to application crash with following
type of errors:

1. Acess Violation Acception
2. Null Reference Acception
3. Invalid Object Acception
4. Application crash dump

Are these issues really a security threat for a desktop application?

We got these errors by sending junk data over the network replies that
this application gets from its web services. However I fail to
understand the security implication and risk of these exceptions.
Since this is a desktop application and not a web service or server
how would these issues impact the security of the desktop application.
The application doesn't open any port on the network for incoming
requests. What would be the best strategy to test such application?
What would be the points from where attacker could attack such a
aplication.

I'll really appreciate some enlightening thoughts on above queries.

Thanx in advance.

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