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Memory leakage in 2-tier applications

The 2-tier applications use front-end to directly communicate to DB. There's no separate business logic tier. All the business logic are at client side. Thick client applications (mostly) are classic examples of that. Applications developed in .Net and Java could be found in big nos. inside any organization. Sometimes it's difficult to straightaway move to 3-tier architecture. Businesses are reluctant to accept this approach due to:
- Moving towards 3-tier involves a great amount of coding efforts and  money.
- Sometimes the applications are almost end of life and are not being retired just because of there;s no good reason to do so. 
- Most of the above applications are Intranet applications. Business claims that being an internal application, this is less susceptible to attack.

But they forget one very big risk under these claims- sensitive information in memory dumps. 

The application being 2-tier connects to DB while constructing the connection string using DB credentials, server name, DB name, port no. etc. These are at risk of being exposed when the client wants to connect to DB. 

But how an attacker can get the dump? He needs to have physical access to the victim's machine. So it's impossible. But we are not talking about an external attacker, we are talking about if the valid user of the application himself turns malicious. He can take the memory dump and find grab the sensitive information such as DB connection string. The soul of an application, ie, DB is compromised, bypassing the business layer. The business doesn't understand this.

So, any fix? There's no fix! As long as the app is 2-tier, there's no fix. However there are compensating controls- make it hard to grab the info from memory. 
- SecureString class- https://msdn.microsoft.com/en-/library/system.security.securestring(v=vs.110).aspx 
But only supported for .Net 4.5 and above. Represents text that should be kept confidential, such as by deleting it from computer memory when no longer needed. This class cannot be inherited.

- Write own code to overwrite the memory location- garbage collection. I saw a code by one developer which does it, to avoid password being exposed in memory. But you have to construct the connectionstring at some point of time, even momentarily, so that the app will connect to the DB and then quickly overwrite that. This reduces the attack window by a large extent- but not fixes it.

There's no real fix than moving to 3-tier architecture.For  2-tier we have to accept the risk.

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