|By Lori MacVittie||
|May 1, 2014 09:00 AM EDT||
This week's "bad news" with respect to information security centers on Facebook and the exploitation of HTTP caches to affect a DDoS attack. Reported as a 'vulnerability', this exploit takes advantage of the way the application protocol is designed to work. In fact, the same author who reports the Facebook 'vulnerability' has also shown you can use Google to do the same thing. Just about any site that enables you to submit content containing links and then retrieves those links for you (for caching purposes) could be used in this way. It's not unique to Facebook or Google, for that matter, they just have the perfect environment to make such an exploit highly effective.
The exploit works by using a site (in this case Facebook) to load content and takes advantage of the general principle of amplification to effectively DDoS a third-party site. This is a flood-based like attack, meaning it's attempting to overwhelm a server by flooding it with requests that voraciously consume server-side resources and slow everyone down - to the point of forcing it to appear "down" to legitimate users.
The requests brokered by Facebook are themselves 110% legitimate requests. The requests for an image (or PDF or large video file) are well-formed, and nothing about the requests on an individual basis could be detected as being an attack. This is, in part, why the exploit works: because the individual requests are wholly legitimate requests.
How it Works
The trigger for the "attack" is the caching service. Caches are generally excellent at, well, caching static objects with well-defined URIs. A cache doesn't have a problem finding /myimage.png. It's either there, or it's not and the cache has to go to origin to retrieve it. Where things get more difficult is when requests for content are dynamic; that is, they send parameters that the origin server interprets to determine which image to send, e.g. /myimage?id=30. This is much like an old developer trick to force the reload of dynamic content when browser or server caches indicate a match on the URL. By tacking on a random query parameter, you can "trick" the browser and the server into believing it's a brand new object, and it will go to origin to retrieve it - even though the query parameter is never used. That's where the exploit comes in.
HTTP servers accept as part of the definition of a URI any number of variable query parameters. Those parameters can be ignored or used at the discretion of the application. But when the HTTP server is looking to see if that content has been served already, it does look at those parameters. The reference for a given object is its URL, and thus tacking on a query parameter forces (or tricks if you prefer) the HTTP server to believe the object has never been served before and thus can't be retrieved from a cache.
Caches act on the same principles as an HTTP server because when you get down to brass tacks, a cache is a very specialized HTTP server, focused on mirroring content so it's closer to the user.
<img src=http://target.com/file?r=1> <img src=http://target.com/file?r=2> <img src=http://target.com/file?r=3> ... <img src=http://target.com/file?r=1000>
Many, many, many, many (repeat as necessary) web applications are built using such models. Whether to retrieve text-based content or images is irrelevant to the cache. The cache looks at the request and, if it can't match it somehow, it's going to go to origin.
Which is what's possible with Facebook Notes and Google. By taking advantage of (exploiting) this design principle, if a note crafted with multiple image objects retrieved via a dynamic query is viewed by enough users at the same time, the origin can become overwhelmed or its network oversubscribed.
This is what makes it an exploit, not a vulnerability. There's nothing wrong with the behavior of these caches - they are working exactly as they were designed to act with respect to HTTP. The problem is that when the protocol and caching behavior was defined, such abusive behavior was not considered.
In other words, this is a protocol exploit not specific to Facebook (or Google). In fact, similar exploits have been used to launch attacks in the past. For example, consider some noise raised around WordPress in March 2014 that indicated it was being used to attack other sites by bypassing the cache and forcing a full reload from the origin server:
If you notice, all queries had a random value (like “?4137049=643182″) that bypassed their cache and force a full page reload every single time. It was killing their server pretty quickly.
But the most interesting part is that all the requests were coming from valid and legitimate WordPress sites. Yes, other WordPress sites were sending that random requests at a very large scale and bringing the site down.
The WordPress exploit was taking advantage of the way "pingbacks" work. Attackers were using sites to add pingbacks to amplify an attack on a third party site (also, ironically, a WordPress site).
It's not just Facebook, or Google - it's inherent in the way caching is designed to work.
Not Just HTTP
This isn't just an issue with HTTP. We can see similar behavior in a DNS exploit that renders DNS caching ineffective as protection against certain attack types. In the DNS case, querying a cache with a random host name results in a query to the authoritative (origin) DNS service. If you send enough random host names at the cache, eventually the DNS service is going to feel the impact and possibly choke.
In general, these types of exploits are based on protocol and well-defined system behavior. A cache is, by design, required to either return a matching object if found or go to the origin server if it is not. In both the HTTP and DNS case, the caching services are acting properly and as one would expect.
The problem is that this proper behavior can be exploited to affect a DDoS attack - against third-parties in the case of Facebook/Google and against the domain owner in the case of DNS.
These are not vulnerabilities, they are protocol exploits. This same "vulnerability" is probably present in most architectures that include caching. The difference is that Facebook's ginormous base of users allows for what is expected behavior to quickly turn into what looks like an attack.
The general consensus right now is the best way to mitigate this potential "attack" is to identify and either rate limit or disallow requests coming from Facebook's crawlers by IP address. In essence, the suggestion is to blacklist Facebook (and perhaps Google) to keep it from potentially overwhelming your site.
The author noted in his post regarding this exploit that:
Facebook crawler shows itself as facebookexternalhit. Right now it seems there is no other choice than to block it in order to avoid this nuisance.
The post was later updated to note that blocking by agent may not be enough, hence the consensus on IP-based blacklisting.
The problem is that attackers could simply find another site with a large user base (there are quite a few of them out there with the users to support a successful attack) and find the right mix of queries to bypass the cache (cause caches are a pretty standard part of a web-scale infrastructure) and voila! Instant attack.
Blocking Facebook isn't going to stop other potential attacks and it might seriously impede revenue generating strategies that rely on Facebook as a channel. Rate limiting based on inbound query volume for specific content will help mitigate the impact (and ensure legitimate requests continue to be served) but this requires some service to intermediate and monitor inbound requests and, upon seeing behavior indicative of a potential attack, the ability to intercede or apply the appropriate rate limiting policy. Such a policy could go further and blacklist IP addresses showing sudden increases in requests or simply blocking requests for the specified URI in question - returning instead some other content.
Another option would be to use a caching solution capable of managing dynamic content. For example, F5 Dynamic Caching includes the ability to designate parameters as either indicative of new content or not. That is, the caching service can be configured to ignore some (or all) parameters and serve content out of cache instead of hammering on the origin server.
Let's say the URI for an image was: /directory/images/dog.gif?ver=1;sz=728X90 where valid query parameters are "ver" (version) and "sz" (size). A policy can be configured to recognize "ver" as indicative of different content while all other query parameters indicate the same content and can be served out of cache. With this kind of policy an attacker could send any combination of the following and the same image would be served from cache, even though "sz" is different and there are random additional query parameters.
/directory/images/dog.gif?ver=1;sz=728X90; id=1234 /directory/images/dog.gif?ver=1;sz=728X900; id=123456 /directory/images/dog.gif?ver=1;sz=728X90; cid=1234
By placing an application fluent cache service in front of your origin servers, when Facebook (or Google) comes knocking, you're able to handle the load.
There have been no reports of an attack stemming from this exploitable condition in Facebook Notes or Google, so blacklisting crawlers from either Facebook or Google seems premature. Given that this condition is based on protocol behavior and system design and not a vulnerability unique to Facebook (or Google), though, it would be a good idea to have a plan in place to address, should such an attack actually occur - from there or some other site.
You should review your own architecture and evaluate its ability to withstand a sudden influx of dynamic requests for content like this, and put into place an operational plan for dealing with it should such an event occur.
For more information on protecting against all types of DDoS attacks, check out a new infographic we’ve put together here.
Performance is the intersection of power, agility, control, and choice. If you value performance, and more specifically consistent performance, you need to look beyond simple virtualized compute. Many factors need to be considered to create a truly performant environment. In their General Session at 15th Cloud Expo, Phil Jackson, Development Community Advocate at SoftLayer, and Harold Hannon, Sr. Software Architect at SoftLayer, to discuss how to take advantage of a multitude of compute option...
Sep. 25, 2014 03:30 PM EDT Reads: 1,869
Come learn about what you need to consider when moving your data to the cloud. In her session at 15th Cloud Expo, Skyla Loomis, a Program Director of Cloudant Development at Cloudant, will discuss the security, performance, and operational implications of keeping your data on premise, moving it to the cloud, or taking a hybrid approach. She will use real customer examples to illustrate the tradeoffs, key decision points, and how to be successful with a cloud or hybrid cloud solution.
Sep. 22, 2014 10:00 PM EDT Reads: 2,371
In today's application economy, enterprise organizations realize that it's their applications that are the heart and soul of their business. If their application users have a bad experience, their revenue and reputation are at stake. In his session at 15th Cloud Expo, Anand Akela, Senior Director of Product Marketing for Application Performance Management at CA Technologies, will discuss how a user-centric Application Performance Management solution can help inspire your users with every appli...
Sep. 22, 2014 03:30 PM EDT Reads: 2,020
With the explosion of the cloud, more businesses are transitioning to a recurring revenue model to generate reliable sales, grow profits, and open new markets. This opportunity requires businesses to get to market quickly with the pricing and packaging options customers want. In addition, you will want to take advantage of the ensuing tidal wave of data to more effectively upsell, cross-sell and manage your customers. All of this is possible, but only with the right approach. At 15th Cloud Exp...
Sep. 12, 2014 11:45 PM EDT Reads: 1,520
Planning scalable environments isn't terribly difficult, but it does require a change of perspective. In his session at 15th Cloud Expo, Phil Jackson, Development Community Advocate for SoftLayer, will broaden your views to think on an Internet scale by dissecting a video publishing application built with The SoftLayer Platform, Message Queuing, Object Storage, and Drupal. By examining a scalable modular application build that can handle unpredictable traffic, attendees will able to grow your de...
Sep. 12, 2014 11:30 PM EDT Reads: 1,826
The cloud provides an easy onramp to building and deploying Big Data solutions. Transitioning from initial deployment to large-scale, highly performant operations may not be as easy. In his session at 15th Cloud Expo, Harold Hannon, Sr. Software Architect at SoftLayer, will discuss the benefits, weaknesses, and performance characteristics of public and bare metal cloud deployments that can help you make the right decisions.
Sep. 11, 2014 10:30 PM EDT Reads: 2,302
Over the last few years the healthcare ecosystem has revolved around innovations in Electronic Health Record (HER) based systems. This evolution has helped us achieve much desired interoperability. Now the focus is shifting to other equally important aspects – scalability and performance. While applying cloud computing environments to the EHR systems, a special consideration needs to be given to the cloud enablement of Veterans Health Information Systems and Technology Architecture (VistA), i.e....
Sep. 10, 2014 06:30 PM EDT Reads: 3,720
Cloud and Big Data present unique dilemmas: embracing the benefits of these new technologies while maintaining the security of your organization’s assets. When an outside party owns, controls and manages your infrastructure and computational resources, how can you be assured that sensitive data remains private and secure? How do you best protect data in mixed use cloud and big data infrastructure sets? Can you still satisfy the full range of reporting, compliance and regulatory requirements? I...
Sep. 10, 2014 03:00 PM EDT Reads: 2,803
Scott Jenson leads a project called The Physical Web within the Chrome team at Google. Project members are working to take the scalability and openness of the web and use it to talk to the exponentially exploding range of smart devices. Nearly every company today working on the IoT comes up with the same basic solution: use my server and you'll be fine. But if we really believe there will be trillions of these devices, that just can't scale. We need a system that is open a scalable and by using...
Sep. 6, 2014 06:45 PM EDT Reads: 5,112
Is your organization struggling to deal with skyrocketing volumes of digital assets? The amount of data is growing exponentially and organizations are having a hard time managing this growth. In his session at 15th Cloud Expo, Amar Kapadia, Senior Director of Open Cloud Strategy at Seagate, will walk through the essential considerations when developing a cloud storage strategy. In this discussion, you will understand the challenges IT is facing, why companies need to move to cloud, and how the...
Sep. 6, 2014 02:00 PM EDT Reads: 1,817
If cloud computing benefits are so clear, why have so few enterprises migrated their mission-critical apps? The answer is often inertia and FUD. No one ever got fired for not moving to the cloud – not yet. In his session at 15th Cloud Expo, Michael Hoch, SVP, Cloud Advisory Service at Virtustream, will discuss the six key steps to justify and execute your MCA cloud migration.
Sep. 6, 2014 11:00 AM EDT Reads: 1,843
The 16th International Cloud Expo announces that its Call for Papers is now open. 16th International Cloud Expo, to be held June 9–11, 2015, at the Javits Center in New York City brings together Cloud Computing, APM, APIs, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speak...
Sep. 5, 2014 02:15 PM EDT Reads: 3,041
Most of today’s hardware manufacturers are building servers with at least one SATA Port, but not every systems engineer utilizes them. This is considered a loss in the game of maximizing potential storage space in a fixed unit. The SATADOM Series was created by Innodisk as a high-performance, small form factor boot drive with low power consumption to be plugged into the unused SATA port on your server board as an alternative to hard drive or USB boot-up. Built for 1U systems, this powerful devic...
Sep. 4, 2014 07:15 PM EDT Reads: 9,073
SYS-CON Events announced today that Gridstore™, the leader in software-defined storage (SDS) purpose-built for Windows Servers and Hyper-V, will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Gridstore™ is the leader in software-defined storage purpose built for virtualization that is designed to accelerate applications in virtualized environments. Using its patented Server-Side Virtual C...
Sep. 4, 2014 01:45 PM EDT Reads: 2,387
SYS-CON Events announced today that Cloudian, Inc., the leading provider of hybrid cloud storage solutions, has been named “Bronze Sponsor” of SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. Cloudian is a Foster City, Calif.-based software company specializing in cloud storage. Cloudian HyperStore® is an S3-compatible cloud object storage platform that enables service providers and enterprises to bui...
Sep. 3, 2014 07:00 PM EDT Reads: 3,313
SYS-CON Events announced today that TechXtend (formerly Programmer’s Paradise), a leading value-added provider of server and storage virtualization, and r-evolution will exhibit at SYS-CON's 15th International Cloud Expo®, which will take place on November 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA. TechXtend (formerly Programmer’s Paradise) is a leading value-added provider of software, systems and solutions for corporations, government organizations, and academic instit...
Sep. 3, 2014 01:00 PM EDT Reads: 2,585
Every healthy ecosystem is diverse. This is especially true in cloud ecosystems, where portability and interoperability are more important than old enterprise models of proprietary ownership. In his session at 15th Cloud Expo, Mark Baker, Server Product Manager at Canonical/Ubuntu, will discuss how single vendors used to take the lead in creating and delivering technology, but in a cloud economy, where users want tools of their preference, when and where they need them, it makes no sense.
Sep. 3, 2014 09:00 AM EDT Reads: 2,667
The consumption economy is here and so are cloud applications and solutions that offer more than subscription and flat fee models and at the same time are available on a pure consumption model, which not only reduces IT spend but also lowers infrastructure costs, and offers ease of use and availability. In their session at 15th Cloud Expo, Ermanno Bonifazi, CEO & Founder of Solgenia, and Ian Khan, Global Strategic Positioning & Brand Manager at Solgenia, will discuss this shifting dynamic with ...
Sep. 2, 2014 11:00 PM EDT Reads: 1,525
The emergence of cloud computing and Big Data warrants a greater role for the PMO to successfully manage enterprise transformation driven by these powerful trends. As the adoption of cloud-based services continues to grow, a governance model is needed to orchestrate enterprise cloud implementations and harness the power of Big Data analytics. In his session at 15th Cloud Expo, Mahesh Singh, President of BigData, Inc., to discuss how the Enterprise PMO takes center stage not only in developing th...
Sep. 2, 2014 11:00 PM EDT Reads: 1,985
Cloud computing started a technology revolution; now DevOps is driving that revolution forward. By enabling new approaches to service delivery, cloud and DevOps together are delivering even greater speed, agility, and efficiency. No wonder leading innovators are adopting DevOps and cloud together! In his session at DevOps Summit, Andi Mann, Vice President of Strategic Solutions at CA Technologies, will explore the synergies in these two approaches, with practical tips, techniques, research dat...
Sep. 2, 2014 02:30 PM EDT Reads: 3,839