• What is WAF?

If your first response to the subject is "What is a Web Application Firewall?", Apologies but I respectfully defer you to the OWASP team who has a great definition posted at: [http://www.owasp.org/index.php/Web_Application_Firewall].  For those who would like extended reading material into the subject of WAF technologies, refer to: [http://www.webappsec.org/projects/wafec/].

• PCI and WAF

Opinion: Growth in the Web Application Firewall space may be attributed somewhat to changes in the Payment Card Industry's (PCI) Data Security Standard [https://www.pcisecuritystandards.org] where integration of an "Application layer firewall" [legacy term] or "Web Application firewall" technology previously listed as 'best practice' had been modified mid-2008 to become a requirement.  WAF technology is now required tooling in the protection of public facing web applications especially where hosts are determined to be financially significant or financial data [credit card detail] is processed.

• WAF geeks unite and take over?
  

I consider myself a geek in the art of WAF and place tremendous value on the visibility I gain into HTTP client traffic.  I depend on client traffic visibility for threat/abuse discovery purposes combined with the mitigation capability afforded by WAF for the gratuitous stomping out badness.  HTTP traffic visibility may seem trivial, until you contemplate the impossible if not an extreme PITA this becomes especially when HTTP services are SSL enabled.  The deployment of traditional IDS sniffer mode detection capabilities are no longer suitable for identifying HTTP borne threats within SSL enabled web applications [aside from a few SSL negotiation flaws ;)] without significant expense and the operational changes required to enable IDS sensors with SSL payload visibility. 

Speaking from personal experience, I am a huge fan of ModSecurity [http://www.modsecurity.org].  ModSecurity while open-source is specific to Apache, and covers the lions share of web apps that I have responsibility in protecting.  I do try to keep my eyes open for equivalent technologies that extend to other web server technology deployments where the underlying web server choice cannot be migrated for various reasons.  While I have experimented with ModSecurity in reverse proxy mode to protect IIS and other server product hosted web services and web apps, I have a mix of IIS services that depend on Microsoft's URLScan filter to provide a subset of equivalent ModSecurity functionality.  I have recently been turned onto to another open-source WAF named 'WebKnight' for Microsoft IIS server deployment.  Based on available documentation it provides functionality that goes beyond basic URLScan features.  However, my recent fifteen minute experiment in deploying WebKnight to a test environment was unsuccessful (I myself must RTFM), though I do plan on giving it proper evaluation time in the near future.

• Share your experiences with WAF

I am most interested in hearing from readers on their experience with WAF technologies, whether they be open or commercial.  I'm keenly interested in constructive product opinions, alternate solutions for server technologies not mentioned, your lessons learned, pitfalls or any success stories you are willing to share.  If you happen to be doing something particularly exciting or know of other projects in the web application protection space that deserve attention, please share!  Pending reader response, results may be posted to a future diary.

• WAF Links:

ModSecurity : [http://www.modsecurity.org]
IIS UrlScan   : [http://www.microsoft.com/downloads/details.aspx?FamilyId=EE41818F-3363-4E24-9940-321603531989&displaylang=en]
WebKnight   : [http://www.aqtronix.com/?PageID=99]

Apologies in advance to all who like clickable URLs in their articles.  It is my bit in avoiding the reinforcement of poor client user practices.

William Salusky
Handler on Duty - :)