It occurred to me while I was writing another blog that we need to talk about Web Application Firewalls (WAF). We think everyone should use one. Your current network and security infrastructure is the castle and drawbridge, whereas WAF is your portcullis. Not securing your applications is like giving away the keys to your kingdom.

What is a WAF?

WAFs are the first and last line of defense for your application. A WAF takes over at layer 4 of the Open Systems Interconnection (OSI) model, moves up to layer 7, and looks at the request, response, and payload. It validates data and the package it’s carried in, and its authenticity. In essence, a WAF applies a set of security rules to all aspects of an HTTP conversation.

The difference from your next-generation firewalls (NGFW) and IDS/IPS units, which only inspect packet-by-packet, is that a WAF digs into HTTP content and conversations, and validates the content request, response, and payload against white and black lists. Using predefined signatures or behavioral baselines, the WAF takes appropriate countermeasures based on configured policy elements. WAFs also include enhanced logging, alerting, connection intermediation, and even content manipulation to mitigate the impacts of attacks, mislead attackers, or inject content designed to raise confidence levels for WAF detection mechanisms.

A WAF validates traffic and payloads by learning the way the application should work, prevents bad input or manipulations, and prevents dangerous query/responses. A WAF maintains HTTP RFC compliance on all aspects of the session, and enforces session rules and session flows. It is a multifaceted tool.

F5 Networks Application Security Manager (ASM), in my opinion, is the right tool for the job. It is a tool that complements the F5 Global Traffic Manager (GTM) and Local Traffic Manager (LTM) devices you already use. To illustrate this, let us look at the traffic flow.

First, the GTM picks up the DNS request. Utilizing GTM, you can create a high-speed query frontend with DNS Express and can secure that zone with DNSSEC. GTM also evaluates your DNS request and traffic-shapes your response based on a host of criteria and settings, sending your session on to the network.

Sure, you have a firewall at your internet edge. It might even be next-gen, performs packet inspection, and has some signatures to eliminate some bad traffic. The same might also be true of your IPS/IDS, but these are packet-by-packet inspections and not the whole HTTP conversation (for the most part) and bad traffic gets by.

Here is where the F5 picks up and starts defending. LTM gets the traffic first and blocks malicious IPs, sorts out countries you may or may not want, defends against DDoS, and mitigates ciphers that are too weak or broken, all while restricting IP/port/landing page. LTM also traffic shapes it handoff to the next level, ASM.

ASM starts slow and builds in levels based on policy. It receives that traffic and checks if it matches the defined site. Then it checks to see if it is a new session. From there, it starts checking everything. It checks against signatures, RFC compliance, session-tracking info, methods, request timing, number of requests, header information, etc. And this is only the initial request. We haven’t even gotten to response!

ASM comes with quick-start policy templates for a ton of popular application templates like Exchange, Sharepoint, PeopleSoft, SAP, etc. If one of those doesn’t fit your build, ASM ships with an auto-policy builder. Fire this up and you turn your ASM device into Sherlock Holmes. It watches traffic pass through and automatically starts writing its own suggestions. When those suggestions get enough hits, ASM makes them into policy. The longer it runs, the better the policy.

If you change the application or add to it, it automatically picks that up and starts the building piece again. You can even build policy without affecting users. By keeping it out of blocking mode, you can mature the policy and reduce the likelihood that false alarms will create negative impact for users.

The ASM comes with other cool features, too, such as preventing forceful browsing, where attackers try to gain access to pages not part of the site that might have admin access. You can keep users from bookmarking deep into the app and redirect them to login pages you defined first to define flow. This keeps the application more secure and enables the organization to track sessions to support security, problem resolution, and compliance use-cases.

With this information, you can restrict application access to secondary login pages or other admin-related content by enforcing application flows and protect against webscraping. Brute force protection will even keep those login pages safe by adding a layer of protection including limiting login attempts, identifying automated attacks and more for these critical security entry points for the application.

DataGuard is an awesome feature as well. It protects sensitive fields like credit card numbers, Social Security numbers, and other administrator-defined sensitive data from passing through clear text. Instead, it utilizes masking to overwrite these values in responses with ‘****’. ASM will also mask these in the logs so you don’t have to worry about admins having access to that info as well.

There are so many other features, including signatures and security responses for common web application security threats such as cross-site request forgery (CSRF), cross-site scripting (XSS), clickjacking, cookie manipulation, etc. Any of these topics, as well as the mechanisms ASM utilizes to protect against them, would be worthy of their own blog post.  

I hope this blog has sparked a little more interest in your traffic and maybe even a hard look into the available security measures you can take. If you are already a Guidepoint Security customer, reach out to your representative to learn more. If you are not a customer and would like to learn more, please feel free to reach out to us. We have several ASM certified engineers to answer your questions. For more information, email

About GuidePoint Security
GuidePoint Security LLC provides innovative and valuable cyber security solutions and expertise that enable organizations to successfully achieve their mission. By embracing new technologies, GuidePoint Security helps clients recognize the threats, understand the solutions, and mitigate the risks present in their evolving IT environments. Headquartered in Herndon, Virginia, GuidePoint Security is a small business, and classification is with the System for Award Management (SAM). Learn more at: