SYS-CON MEDIA Authors: Pat Romanski, Gary Arora, Zakia Bouachraoui, Yeshim Deniz, Liz McMillan

Blog Feed Post

20 Lines or Less #53: Security, Security & more Security

What could you do with your code in 20 Lines or Less? That's the question I ask (sometimes?) every week for the DevCentral community, and every week I go looking to find cool new examples that show just how flexible and powerful iRules can be without getting in over your head.

This week we've got three awesome examples of iRules that are designed to increase your application's security in less than 21 lines of code. Dealing with header size, cache control, and a Microsoft advisory, we get to see a couple of different ways in which iRules can save the day. This isn't a new theme. iRules can be an amazingly powerful security resource in the hands of someone with the security mindset to be aware of what is going on, and the F5/iRules knowledge to craft the solutions necessary to put in place the preventative measures necessary to thwart incoming attacks.

Preventing Overzealous Headers

To work around a recently released bug that allowed attackers to exploit excess parameters in an HTTP request, Aaron whipped up an iRule to count the parameters. User Wizdem had an excellent start, looking through the payload, but Aaron and Jason teamed up to make it more efficient and expanding it to look through the query string as well. If either of these have more than 100 parameters, it drops the request, assuming it to be an attack. Given that most requests shouldn't have anywhere near 100 parameters, that should be a pretty safe assumption, but your mileage may vary, as always. A very slick look at an iRule protecting against a known attack in a short period of time with only a few lines of code. This one looks longer than it is. Take out white space, comments, and log lines and you end up at 20. Honest.

   1: when HTTP_REQUEST {
   3:     # Check if the query string contains more than 100 parameters
   4:     if { [llength [split [HTTP::query] &]] > 100 } {
   5:         log local0.alert "Microsoft Security Advisory (2659883)\
   6:             IP Address [IP::client_addr]:[TCP::client_port] requested [HTTP::uri]"
   8:         # Drop the request
   9:         drop
  10:         return
  11:     }
  13:     # Collect up to 1Mb of POST data
  14:     if { [HTTP::method] equals "POST"}{ 
  15:         set clength 0
  16:     if {[HTTP::header "Content-Length"] ne "" && [HTTP::header "Content-Length"] <= 1048576 && [HTTP::header "Content-Length"] > 0}{ 
  17:            set clength [HTTP::header Content-Length]
  18:         } else { 
  19:             set clength 1048576 
  20:         }
  21:         HTTP::collect $clength
  22:     }
  23: }
  25: when HTTP_REQUEST_DATA {
  27:     # Check if the collected payload contains more than 100 parameters
  28:     if { [llength [split [HTTP::payload] &]] > 100 } {
  29:         log local0.alert "Microsoft Security Advisory (2659883)\
  30:             IP Address [IP::client_addr]:[TCP::client_port] requested [HTTP::uri]"
  32:         # Drop the request
  33:         drop
  34:     }
  35: }

Header Size Restrictions

Similar yet different, in this snippet the size of each header is inspected to ensure it is not over 1000 characters. While this is not necessarily a malicious attack it was causing problems for the OP in the thread, and Aaron was kind enough to lend an updated version to log the header lengths as they come through, since this thread was brought back up recently. In this incarnation the rule is only logging but it would be trivial to modify it to drop requests as necessary if you experience a particular client attempting to send through egregiously large headers in an attempt to cause problems.

   1: when HTTP_REQUEST {
   3:     # Check the total HTTP headers size
   4:     if {[string length [HTTP::request]] > 10000 }{
   6:         # Loop through the headers by name
   7:         foreach header {[HTTP::header names]} { 
   9:             # Check for a long header value
  10:             if {[string length [HTTP::header value $header]] > 1000 } { 
  11:                 log local0. "Header is long. Header Name: $header,\
  12:                     Length: [string length [HTTP::header value $header]], Value: [HTTP::header value $header]" 
  13:             }
  14:         }
  15:     }
  16: }

No-Cache ... For Real

In this post user Joanna shares the problem she's facing with us

"The problem is that Google Chrome will cache, in the current sessions memory only,  responses which have had the no-cache directive applied.  This means that after a user logs out of an application and walks away,  another user can come up to the computer,  press the back arrow and potentially see private information.  The way round this is to use the no-store directive with a couple of other headers thrown in for good measure. "

That is less than optimal...a browser that refuses to respect no-cache headers for secure pages. I'm not sure in what environments or across which versions this applies, but having a fix readily available is a good thing. Fortunately Joanna was kind enough to provide exactly that. With this simple iRule she was able to more firmly enforce her caching directives and create a more secure application in the process.

   1: when HTTP_RESPONSE {
   2:     # The purpose of this iRule event processing is to force no-store so that browsers will not store this content
   3:     # which would enable users to hit the 'back' button,  even after a logout,  and potentially see customer PII
   6:     if {[HTTP::header Content-Type] contains "html"} {
   7:         HTTP::header insert Pragma "no-cache"
   8:         HTTP::header insert Expires "Fri, 01 Jan 1990 00:00:00 GMT"
   9:        HTTP::header replace Cache-Control "no-cache,no-store,must-revalidate"
  10:     }
  11: }

There you have it, <= 60 lines of code to help make your iRuling life better, more interesting and in this case more secure, too. More iRules goodness is sure to follow in coming weeks.


Read the original blog entry...

More Stories By Colin Walker

Coming from a *Nix Software Engineering background, Colin is no stranger to long hours of coding, testing and deployment. His personal experiences such as on-stage performance and the like have helped to foster the evangelist in him. These days he splits his time between coding, technical writing and evangalism. He can be found on the road to just about anywhere to preach the good word about ADCs, Application Aware networking, Network Side Scripting and geekery in general to anyone that will listen.

Colin currently helps manage and maintain DevCentral ( He is also a contributor in many ways, from Articles to Videos to numerous forum posts, to iRules coding and whatever else he can get his hands on that might benefit the community and allow it to continue to grow.

Latest Stories
Every organization is facing their own Digital Transformation as they attempt to stay ahead of the competition, or worse, just keep up. Each new opportunity, whether embracing machine learning, IoT, or a cloud migration, seems to bring new development, deployment, and management models. The results are more diverse and federated computing models than any time in our history.
On-premise or off, you have powerful tools available to maximize the value of your infrastructure and you demand more visibility and operational control. Fortunately, data center management tools keep a vigil on memory contestation, power, thermal consumption, server health, and utilization, allowing better control no matter your cloud's shape. In this session, learn how Intel software tools enable real-time monitoring and precise management to lower operational costs and optimize infrastructure...
"Calligo is a cloud service provider with data privacy at the heart of what we do. We are a typical Infrastructure as a Service cloud provider but it's been designed around data privacy," explained Julian Box, CEO and co-founder of Calligo, in this interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Isomorphic Software is the global leader in high-end, web-based business applications. We develop, market, and support the SmartClient & Smart GWT HTML5/Ajax platform, combining the productivity and performance of traditional desktop software with the simplicity and reach of the open web. With staff in 10 timezones, Isomorphic provides a global network of services related to our technology, with offerings ranging from turnkey application development to SLA-backed enterprise support. Leadin...
While a hybrid cloud can ease that transition, designing and deploy that hybrid cloud still offers challenges for organizations concerned about lack of available cloud skillsets within their organization. Managed service providers offer a unique opportunity to fill those gaps and get organizations of all sizes on a hybrid cloud that meets their comfort level, while delivering enhanced benefits for cost, efficiency, agility, mobility, and elasticity.
DevOps has long focused on reinventing the SDLC (e.g. with CI/CD, ARA, pipeline automation etc.), while reinvention of IT Ops has lagged. However, new approaches like Site Reliability Engineering, Observability, Containerization, Operations Analytics, and ML/AI are driving a resurgence of IT Ops. In this session our expert panel will focus on how these new ideas are [putting the Ops back in DevOps orbringing modern IT Ops to DevOps].
Darktrace is the world's leading AI company for cyber security. Created by mathematicians from the University of Cambridge, Darktrace's Enterprise Immune System is the first non-consumer application of machine learning to work at scale, across all network types, from physical, virtualized, and cloud, through to IoT and industrial control systems. Installed as a self-configuring cyber defense platform, Darktrace continuously learns what is ‘normal' for all devices and users, updating its understa...
Enterprises are striving to become digital businesses for differentiated innovation and customer-centricity. Traditionally, they focused on digitizing processes and paper workflow. To be a disruptor and compete against new players, they need to gain insight into business data and innovate at scale. Cloud and cognitive technologies can help them leverage hidden data in SAP/ERP systems to fuel their businesses to accelerate digital transformation success.
Most organizations are awash today in data and IT systems, yet they're still struggling mightily to use these invaluable assets to meet the rising demand for new digital solutions and customer experiences that drive innovation and growth. What's lacking are potent and effective ways to rapidly combine together on-premises IT and the numerous commercial clouds that the average organization has in place today into effective new business solutions.
Concerns about security, downtime and latency, budgets, and general unfamiliarity with cloud technologies continue to create hesitation for many organizations that truly need to be developing a cloud strategy. Hybrid cloud solutions are helping to elevate those concerns by enabling the combination or orchestration of two or more platforms, including on-premise infrastructure, private clouds and/or third-party, public cloud services. This gives organizations more comfort to begin their digital tr...
Keeping an application running at scale can be a daunting task. When do you need to add more capacity? Larger databases? Additional servers? These questions get harder as the complexity of your application grows. Microservice based architectures and cloud-based dynamic infrastructures are technologies that help you keep your application running with high availability, even during times of extreme scaling. But real cloud success, at scale, requires much more than a basic lift-and-shift migrati...
David Friend is the co-founder and CEO of Wasabi, the hot cloud storage company that delivers fast, low-cost, and reliable cloud storage. Prior to Wasabi, David co-founded Carbonite, one of the world's leading cloud backup companies. A successful tech entrepreneur for more than 30 years, David got his start at ARP Instruments, a manufacturer of synthesizers for rock bands, where he worked with leading musicians of the day like Stevie Wonder, Pete Townsend of The Who, and Led Zeppelin. David has ...
Darktrace is the world's leading AI company for cyber security. Created by mathematicians from the University of Cambridge, Darktrace's Enterprise Immune System is the first non-consumer application of machine learning to work at scale, across all network types, from physical, virtualized, and cloud, through to IoT and industrial control systems. Installed as a self-configuring cyber defense platform, Darktrace continuously learns what is ‘normal' for all devices and users, updating its understa...
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Addteq is a leader in providing business solutions to Enterprise clients. Addteq has been in the business for more than 10 years. Through the use of DevOps automation, Addteq strives on creating innovative solutions to solve business processes. Clients depend on Addteq to modernize the software delivery process by providing Atlassian solutions, create custom add-ons, conduct training, offer hosting, perform DevOps services, and provide overall support services.