Since Friday is usually “trash” day (when you dump articles you don’t expect anyone to read) I don’t usually post anything major. But thanks to some unexpected work that hit yesterday, I wasn’t able to get part 2 of this series out when I wanted to. If you can tear yourself away from those LOLCatz long enough, we’re going to talk about web browsers, WAFs, and web application gateways. These are the first two components of Application and Database Monitoring and Protection (ADMP), which I define as:
Products that monitor all activity in a business application and database, identify and audit users and content, and, based on central policies, protect data based on content, context, and/or activity.
As we discussed in part 1, one of the biggest problems in web application security is that the very model of the web browsers and the World Wide Web is not conducive to current security needs. Browsers are the ultimate mashup tool- designed to take different bits from different places and seamlessly render them into a coherent whole. The first time I started serious web application programming (around 1995/96) this blew my mind. I was able to embed disparate systems in ways never before possible. And not only can we embed content within a browser, we can embed browsers within other content/applications. The main reason, as a developer, I converted from Netscape to IE was that Microsoft allowed IE to be embedded in other programs, which allowed us to drop it into our thick VR application. Netscape was stand alone only; seriously limiting its deployment potential.
This also makes life a royal pain on the security front where we often need some level of isolation. Sure, we have the same-origin policy, but browsers and web programming have bloated well beyond what little security that provides. Same-origin isn’t worthless, and is still an important tool, but there are just too many ways around it. Especially now that we all use tabbed browsers with a dozen windows open all the time. Browsers are also stateless by nature, no matter what AJAX trickery we use. XSS and CSRF, never mind some more sophisticated attacks, take full advantage of the weak browser/server trust models that result from these fundamental design issues.
In short, we can’t trust the browser, the browser can’t trust the server, and individual windows/tabs/sessions in the browser can’t trust each other. Fun stuff!
I’ve talked about WAFs before, and their very model is also fundamentally flawed. At least how we use WAFs today. The goal of a WAF is, like a firewall, to drop known bad traffic or only allow known good traffic. We’re trying to shield our web applications from known vulnerabilities, just like we use a regular firewall to block ports, protocols, sources, and destinations. Actually, a WAF is closer to IPS than it is to a stateful packet inspection firewall.
But web apps are complex beasts; every single one a custom application, with custom vulnerabilities. There’s no way a WAF can know all the ins and outs of the application behind it, even after it’s well tuned. WAFs also only protect against certain categories of attacks- mostly some XSS and SQL injection. They don’t handle logic flaws, CSRF, or even all XSS. I was talking with a reference yesterday of one of the major WAFs, and he had no trouble slicing through it during their eval phase using some standard techniques.
To combat this, we’re seeing some new approaches. F5 and WhiteHat have partnered to feed the WAF specific vulnerability information from the application vulnerability assessment. Imperva just announced a similar approach, with a bunch of different partners.
These advances are great to see, but I think WAFs will also need to evolve in some different ways. I just don’t think the model of managing all this from the outside will work effectively enough.
The idea of ADMP is that we build a stack of interconnected security controls from the browser to the database. At all levels we both monitor activity and include enforcement controls. The goal is to start with browser session virtualization connected to a web application gateway/WAF. Then traffic hits the web server and web application server, both with internal instrumentation and anti-exploitation. Finally, transactions drop to the database, where they are again monitored and protected.
All of the components for this model exist today, so it’s not science fiction. We have browser session virtualization, WAFs, SSL-VPNs (that will make sense in a minute), application security services and application activity monitoring, and database activity monitoring. In addition to the pure defensive elements, we’ll also tie in to the applications at the design and code level through security services for adaptive authentication, transaction authentication, and other shared services (happy Dre? 🙂 ). The key is that this will all be managed through a central console via consistent policies.
In my mind, this is the only thing that makes sense. We need to understand the applications and the databases that back them. We have to do something at the browser level since even proper parameterization and server side validation can’t meet all our needs. We have to start looking at transactions, business context, and content, rather than just packets and individual requests.
Point solutions at any particular layer have limited effectiveness. But if we stop looking at our web applications as pieces, and rather design security that addresses them as a whole, we’ll be in much better shape. Not that anything is perfect, but we’re looking at risk reduction, not risk elimination. A web application isn’t just a web server, just some J2EE code, or just a DB- it’s a collection of many elements working together to perform business transactions, and that’s how we need to look at them for effective security.
The Browser and Web Application Gateway
A little while back I wrote about the concept of browser session virtualization. To plagiarize myself and save a little writing time so I can get my behind to happy hour:
What we ideally need is a way to completely isolate our content in the browser. One way to do this is session virtualization, pioneered by GreenBorder, who was later acquired by Google (the GreenBorder site is just in support mode now). When a user connects to our site, we push down some code to create a virtual environment in the browser that we strictly control. We wall off that session, which could just be an isolated iFrame in a page, so that it only accesses content we send it. Basically, we break the normal browser model and hijack what we need. This would, for example, help stop CSRF since other browser elements won’t be able to trigger a connection to our application. Done right, it limits man in the middle attacks, even if the user authorizes a bad digital certificate. To work properly, this needs to be tied to a gateway that controls the session. While we could do it from the web/app server itself, I suspect we’ll see this as a web application firewall feature, just as we see similar features from SSL-VPNs. I think isolated WAFs have a very limited lifespan, but this is exactly the kind of feature that will extend their value. Better yet, we can tie this in to our Application and Database Monitoring and Protection to build a browser-to-database protected path. We can completely track a transaction or piece of content from the database server to the browser and back. We could even use this to isolate out potentially “bad” content in an in-browser sandbox. For example, it could be a way to enable all those social networking widgets in a more controlled way but locking in potentially bad content instead of known good. Will this protect us from keystroke sniffers or a completely compromised host? Nope, but it will definitely help with a large number of our current browser security issues. If we combine it with full ADMP and additional methods like transaction authentication, I think we can regain a bit of control of the web application security mess.
Thus we see one migration path for a WAF. A user goes to connect to the application and hits the WAF, which is now more of a Web Application Gateway. The gateway, like an SSL-VPN, sends the session virtualization code down to the browser. We do this outside of the web application for performance reasons. The secure virtual session is established and the gateway then allows communications with the application behind it.
For things like retail and financial sites that include only limited third party content if any, we can monitor activity from the browser through to the application and work within the isolated session. It both improves our ability to control what’s being sent to the browser, and gives us a higher degree of confidence that what’s coming from the browser is safe. We still validate everything, but since we’re tied to the application itself we can validate in the browser and at the gateway before we even hit the app (and further validate there). Since in a controlled environment we know what transactions should be allowed (or not), we have more ability to detect and block “bad” transactions like SQL injection from the user.
In less controlled environments- thing MySpace or Gmail and everything in between- the gateway also becomes a filter for third party content. Like Checkpoint’s new ForceField. The gateway filters out, to the best of its ability, harmful third party content coming from third party sites. Basically, it becomes an SSL-VPN for secure browsing.
This is obviously not viable for all sites due to bandwidth considerations, and in those circumstances we’ll drop this part and stick to the rest of the ADMP stack, or only virtualize our pieces of content knowing the user is at risk for the third party stuff we’re still linking them to.
Future of the WAF, Option 2
I’ve just described a scenario where the WAF extends into a Secure Web Application Gateway that adds virtualization, encryption, and content filtering. That doesn’t mean WAFs won’t also still exist in non-virtualized situations, since that will still be a massive volume of sites out there.
For these sites the WAF continues to progress with deeper application integration and application understanding, and works with the elements I’ll describe later that will be embedded into the applications and databases. Rather than hanging around outside the application with barely any idea what’s going on behind it, the WAF will take its cues from the app, help manage sessions, and monitor activity outside the app to block the few things we know we can pick up at that layer.
Why use the WAF at all? To give us a choke point and offload some of the monitoring and processing that could hurt application performance. Let’s be honest- maybe WAFs will eventually go away, but performance problems alone will probably keep next-gen WAFs viable for a while. There are also plenty of things we can now block before they ever hit the application controls, which, by nature of being integrated at the app level, will be more complex and delicate.
But again, by tightly integrating with our other layers, instead of naievely assuming that an external black box will magically solve our problems, we get a much higher level of functionality. Feeding in vulnerability data as we’re just starting to do is a good beginning, but once we plug in deeper to the application and database servers we’ll get entirely new levels of functionality.
Part 2 Conclusions
What I’ve described today is how we can build a (more) trusted path from the browser to the face of the application. WAFs will add gateway capabilities, both protecting the applications behind them and the browsers in front of them. Since this won’t be the right approach in all circumstances, WAFs will also evolve with tighter integration to the application and other ADMP stack components.
Again, this might sound like little more than the usual analyst fiction, but all the components are here today. Also, I don’t expect my predictions to be totally accurate. I’m roughly guessing I’m at 85% or so.
Next week I’ll start digging into the application and database. We’ll talk about application instrumentation, anti-exploitation, DAM, trusted transaction paths, and shared security services.