WebApp Sec mailing list archives
Re: Three Physical Tiers in the Name of Security?
From: "Frank O'Dwyer" <fod () littlecatZ com>
Date: Thu, 28 Jul 2005 22:38:35 +0100
One argument for having three tiers is basically a least privilege / containment argument. The idea is that if the web tier and/or credential gets compromised, it can only execute (hopefully) narrowly defined business logic requests against the middle tier, it cannot directly update tables. It is basically the difference between being able to execute raw SQL and stored procedures. The middle tier needs to be suspicious of the web tier for this to work, i.e. it depends what the business logic enforces. But if you didn't make that split, then a compromised web tier would have immediate access to the whole database backend and update/query tables directly, without being constrained by business logic at all. So there is a good reason to get the business logic physically off the web tier, and create a logical middle tier, at least. There is a similar argument for physically splitting the middle tier from the DB, for example if the same DB is accessed by multiple apps, then each middle tier gets the access it needs and no more. But depending on what you are doing you may or may not care about that. Also depends whether you need segregation of duties between those who admin the various tiers. So at least if you're facing a hostile network then it's reasonable to have 3 logical tiers, but that doesn't necessarily mean that the middle & DB tiers couldn't be physically co-located. Cheers, Frank Richard Burgett wrote:
One of our new colleagues is leading the charge to require *all* business logic (i.e. database calls) to be physically located on a middle tier server (which is separate from the Web and DB Server). The motivation for this change is "to be more secure". We're a Microsoft shop, and are finally moving from ASP to ASP.Net for public facing web apps (ones that provide web registrations and similar with a database). I can understand using Three Physical Tiers for the reasons of performance, scalability, and design purposes. But, I've yet to find a compelling reason why to do this for security reasons (after some googling). Could anyone point to some sort of authoritative document on this or give a response? Chapter 7 in the "Building Secure ASP.NET Applications" book has very useful information, I'm just basically trying to see how security mesures up between the 2 physical tier scenario of "ASP.NET to SQL Server" and 3 physical tier scenarios of "ASP.NET to Remote Enterprise Services to SQL Server" (or even "Using .NET Remoting"). Do 2 Physical tiers only cut it for small web sites that don't store things like Credit Card info (i.e. "Grandma's Cookie Shop")? Where would you draw the line for moving to 3 tiers (being a bank)? Upto what level of sensitive info can you store in 2 physical tiers? In trying to look at it from a bad guy's perspective, how much more protection does the extra physical tier give you? (especially in terms of trying to escalating database privilege or trying to penetrate backend systems) I'm not too familiar with these newer technologies in terms of pen-testing, but I imagine it wouldn't be that much harder to "island hop" across the middle tier with netcat (or similar) after gaining access and elevating privileges. (these newer technologies must use open ports that pass through the firewall between servers that could somehow be compromised). We have a fairly low volume of transactions, and were hoping to smoothe out the learning curve for our existing developers that are learning .Net and web stuff and take a more gradual approach. (although some of our apps are small and they all probably don't warrant the extra complexity of this approach). Personally, I don't like the rigid rule of having to create a class on a middle tier for all database calls to populate a web page, but maybe it will grow on me ;) Some of our developers are thinking 3 tiers is actually 3 tears from the eyes, lol Thanks for any feedback, Richard __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Current thread:
- Three Physical Tiers in the Name of Security? Richard Burgett (Jul 27)
- RE: Three Physical Tiers in the Name of Security? Lyal Collins (Jul 28)
- Re: Three Physical Tiers in the Name of Security? Lucas Holt (Jul 28)
- Re: Three Physical Tiers in the Name of Security? Frank O'Dwyer (Jul 28)
- Re: Three Physical Tiers in the Name of Security? Christopher Canova (Jul 28)
- Re: Three Physical Tiers in the Name of Security? Frank O'Dwyer (Jul 29)
- <Possible follow-ups>
- RE: Three Physical Tiers in the Name of Security? Jeff Robertson (Jul 28)
- Re: Three Physical Tiers in the Name of Security? Groves Powers (Jul 28)
- RE: Three Physical Tiers in the Name of Security? Lyal Collins (Jul 28)