Welcome!

Microservices Expo Authors: Elizabeth White, Gregor Petri, Gerardo A Dada, Roger Strukhoff, XebiaLabs Blog

Related Topics: Microservices Expo, Java IoT, Microsoft Cloud, Silverlight, Cloud Security

Microservices Expo: Article

Any Means Possible: Tales from Penetration Testing

Problems centered on web service APIs can potentially be just as dangerous as an SQLi vulnerability

When we aren't fighting crime, taking over the world, or enjoying a good book by the fire, we here on the eEye Research team like to participate in the Any Means Possible (AMP) Penetration Testing engagements with our clients. For us, it's a great way to interact one-on-one with IT folks and really dig into the security problems that they are facing. We can sharpen our skills with real-world scenarios and practice the academic techniques presented in the industry, all the while helping to connect better with our customers and identify their security needs. During these engagements, we target a number of attack surfaces, ranging from exposed external server interfaces to client-side attacks launched on individual workstations. What I would like to talk about today is centered purely on the web-based attack surface, with a common problem we see consistently during our AMP engagements.

When talking about web vulnerabilities, you can't even begin to breach the subject without someone throwing out Cross-Site Scripting (XSS) or SQL Injection (SQLi). Unfortunately, poor little web services never seem to get any attention in the mix. Web service vulnerabilities are arguably just as widespread and dangerous as the aforementioned classes of vulnerabilities, but with so little talk and discussion around them, very rarely are these issues identified and remediated. Let's fix that.

Vulnerabilities in web services stem from the developer's line of thinking that says "I can trust the input from programs that I write." It's true that in some situations data coming from a known source that you wrote can sometimes be trusted. This is not however true when that data communication travels over an untrusted medium, such as the Internet. A common mistake in web design and development that we still see frequently is a server relying on input that was parsed and filtered by the client's browser. An example of such would be JavaScript running in the browser that is doing all of the filtering for malicious characters. Surely the JavaScript has filtered out all characters that could allow an attacker to insert malicious SQL queries into the back-end SQL Database, right? Wrong, any data that the server receives from a client's browser can be sent directly to the server from another, custom-written, application. This means that an attacker can bypass server-provided client-side SQLi and XSS protections by simply sending the queries directly to the server. When traveling over the Internet, it becomes quite difficult to determine the exact means in which the data was sent; it may have never been sent from the application that you intended it to be sent from. This makes exploitation of these vulnerabilities a bit more obscure, but still possible. The same holds true for web service APIs used by client-side applications.

Figure 1: Demo Microsoft Silverlight application. The left is a failed attempt to login and reveal the user's secret data, the right is a successful login.

Many browser applications, such as Adobe Flash and Microsoft Silverlight, communicate back to the server programmatically using web services. These services are exposed interfaces on the server that can be called directly from custom-written applications. In many situations, these services can expose potentially sensitive and privileged information that would otherwise not be accessible. Figure 1 shows a Microsoft Silverlight application that was constructed for demonstration purposes. This application is not vulnerable to XSS or SQLi and, to the average user, there is nothing about this application that allows someone without a password to access the legitimate user's secret data. However, what a lot of people don't seem to take into consideration is that you have access to anything that is running in your browser. Now, we can't pull the entire project down off of the server, but we can reverse-engineer the application interface running in the browser to see if there is anything potentially sensitive that is being exposed.

The first thing that should be done when auditing web sites is to make sure all requests are being logged through a local request proxy. For this example, I will be using Tamper Data (https://addons.mozilla.org/en-US/firefox/addon/tamper-data/) to log all of the requests that FireFox makes to our target Silverlight application. Right away, we see that the application requests an XAP file, shown in Figure 2. This is a fun thing to play around with that I will come back to later. As soon as we click the button on the page, we see the browser make a request to an SVC file; this is our web services interface and is also shown in Figure 2.

Figure 2: Browser makes requests for an XAP file and an SVC file. The XAP file is loaded immediately into the browser when the application is started and the SVC file is loaded as soon as the user attempts to submit data back to the server.

Now, when we find a site serving up an SVC web services file, it's usually game over for that particular site. The reason is that these interfaces are usually trusted by the developer. Developers will assume that the only thing calling these exposed interfaces is the client application that they wrote. However, browsing to the service file directly in your favorite web browser will usually show you the basic interface of the exposed web service. The next step is creating a custom application to interface with the web service directly. You can use any language that you want as long as it can interface with a web server, but I usually like to use C# in Visual Studio. Creating the application is quite easy - simply create a new C# project and add a service reference to the hosted SVC file. Visual Studio will automatically import all of the references to everything exposed by the service. Figure 3 shows what is exposed by the sample service.

Figure 3: Object Viewer's list of the imported Web Services interface.

This service exports two functions: GetUserSecret and Login. The interesting thing here is that GetUserSecret takes a string and gives back a string, likely representing the secret data associated with that provided user. Now, it's perfectly possible that there is some form of authentication check that happens on the server side when this function is called, which ensures no secrets are disclosed to unauthenticated clients. However, in many situations I have encountered, this is not the case. We can test if code is properly checking for authentication by writing our own custom interface for the exposed web service. The following code snippet instantiates a client and queries for the secret data of two users without first authenticating with the server. Figure 4 shows the output from that program.

LoginService.LoginServiceClient client = new LoginService.LoginServiceClient();
Console.WriteLine("eEyeResearch's secret: "+client.GetUserSecret("eEyeResearch"));
Console.WriteLine("admin's secret: " + client.GetUserSecret("admin"));

Figure 4: Output from the code written to call the example service directly.

The output from our code shows that this exposed service is callable directly, without requiring any authentication. The only information needed is the user's name and, as many of you know from attacks that have made the press over the past year, that information can be acquired through social engineering or brute force style attacks quite easily.

This vulnerability is quite straightforward, but I think many of you would be surprised how often we encounter issues very similar to this in real-world penetration testing scenarios. It's a fairly easy mistake to make, to assume that any malicious tampering of a web page would be done through a browser or front-end web application, but the simple truth is that this is not the case.

If you wanted to take this a bit further, you could examine the manifest files that are used by the client-side browser application. Remember the XAP file mentioned at the beginning? That file is actually a ZIP archive containing manifest information and binary executable files used by the Silverlight application. Examining these files will show you all of the web services APIs that the application can potentially call, even the authenticated ones. This information has proven to be quite useful on various engagements. A simple web application, that wasn't vulnerable to XSS or SQLi, revealed a manifest of previously unknown web services, which eventually allowed downloading all of the information hidden behind the login page. Because these services were only referenced after the user had authenticated through the login screen, these APIs may have never been found with a purely unauthenticated audit had the manifest files not been checked for additional exposed interfaces.

As if freely available manifest information wasn't enough, the DLL files presented in this archive can also prove to be a lot of fun. Ask any professional or hobby reverse-code engineer, languages such as Java or C# are quite easy to decompile. Due to the managed nature of such languages, there are actually freely available tools that do quite a good job of turning the compiled binaries back into the original (or very similar) high-level code. These DLLs only represent the client-side browser code that gets executed by Silverlight in the browser, so you won't be getting the original server code out of this. However, a very common mistake made by programmers is to incorporate some of the application logic into the user interface as well. In these situations, such reversing sessions may yield valuable information about how the application is working behind the scenes. In fact, this has been used in the past to gain all kinds of interesting information about target applications, including default credentials to the authenticated sections of the application, which were set in a button click-event handler of the application's user interface.

Though this entire article has been purely focused on Silverlight, the same concept applies to most other client-side web applications out there. Often times, these applications will rely on web services in order to communicate with the server, for both unauthenticated and authenticated communications alike. Developers often times rely on the client-side application to do all of the relevant filtering and data integrity checking of information being sent to these web services.

Along with authenticated actions on behalf of an unauthenticated application, we have used these service APIs to inject malicious data into hosted material. I think my favorite case with that was when we attacked a Flash application as part of an AMP engagement that called a web service API in the background. This API was used to lay text over greeting card images that were being hosted on the affected server. The Flash application filtered input to only allow alphanumeric characters but calling the API directly allowed us to insert malicious JavaScript to sit on top of the images. Upon viewing the page or the image link directly, we gained the ability to execute arbitrary JavaScript in the user's browser or embed hidden iFrames that could be used to host various exploits. The basic point here is that successful exploitation can yield a variety of things for the attacker. This isn't something that, when exploited, only dumps information or only changes the way a page is viewed; the limits of these vulnerabilities is only determined by the functionality of the web application.

Problems centered on web service APIs can potentially be just as dangerous as an SQLi vulnerability. It's somewhat unfortunate that SQLi has become so trendy, taking away any deserved fame or glory from the other interesting web vulnerabilities. It's important to keep in mind that, though this was a very heavily focused Microsoft and Silverlight example, the same issues apply across the board in many different web application technologies. The issue is actually very easy to audit for, especially if you already know exactly what your application should and shouldn't be able to do at every level of authentication.

I recommend if you manage servers hosting websites or you manage the websites that you take a few minutes to sit down and browse through each of these services. Be aware of exactly what is exposed on the external facing interfaces. If anything looks out of place, try connecting directly to the service and see what information is exposed and available to your users. Try preventing the service from displaying its metadata by removing the mex endpoint binding and setting httpGetEnabled for service metadata to false in the web configuration file. This prevents users from reading the web services descriptions and makes it nontrivial to arbitrarily connect and communicate with these services without prior knowledge of the internal workings of the application. These problems are quite easy to identify, potentially trivial to remediate, and can save an organization from a serious compromise if steps are taken to proactively identify and address these issues.

•   •   •

This article was written by Jared Day, a researcher with eEye's Research Team led by Marc Maiffret.

If you are interested in learning more about our AMP services, you can visit our page here (http://www.eeye.com/services/penetration-testing).

More Stories By Jared Day

Jared Day, Security Research Engineer, eEye Research Team. He joined the research team in 2010 and works primarily as a security advocate for eEye clients; participating and leading the Any Means Possible (AMP) Penetration Tests, as well as custom private research related to malware, threat, and patch mitigation analysis.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@MicroservicesExpo Stories
Kubernetes is a new and revolutionary open-sourced system for managing containers across multiple hosts in a cluster. Ansible is a simple IT automation tool for just about any requirement for reproducible environments. In his session at @DevOpsSummit at 18th Cloud Expo, Patrick Galbraith, a principal engineer at HPE, discussed how to build a fully functional Kubernetes cluster on a number of virtual machines or bare-metal hosts. Also included will be a brief demonstration of running a Galera MyS...
About a year ago we tuned into “the need for speed” and how a concept like "serverless computing” was increasingly catering to this. We are now a year further and the term “serverless” is taking on unexpected proportions. With some even seeing it as the successor to cloud in general or at least as a successor to the clouds’ poorer cousin in terms of revenue, hype and adoption: PaaS. The question we need to ask is whether this constitutes an example of Hype Hopping: to effortlessly pivot to the ...
Today’s IT environments are increasingly heterogeneous, with Linux, Java, Oracle and MySQL considered nearly as common as traditional Windows environments. In many cases, these platforms have been integrated into an organization’s Windows-based IT department by way of an acquisition of a company that leverages one of those platforms. In other cases, the applications may have been part of the IT department for years, but managed by a separate department or singular administrator. Still, whether...
As we enter the final week before the 19th International Cloud Expo | @ThingsExpo in Santa Clara, CA, it's time for me to reflect on six big topics that will be important during the show. Hybrid Cloud: This general-purpose term seems to provide a comfort zone for many enterprise IT managers. It sounds reassuring to be able to work with one of the major public-cloud providers like AWS or Microsoft Azure while still maintaining an on-site presence.
I’m a huge fan of open source DevOps tools. I’m also a huge fan of scaling open source tools for the enterprise. But having talked with my fair share of companies over the years, one important thing I’ve learned is that you can’t scale your release process using open source tools alone. They simply require too much scripting and maintenance when used that way. Scripting may be fine for smaller organizations, but it’s not ok in an enterprise environment that includes many independent teams and to...
Get deep visibility into the performance of your databases and expert advice for performance optimization and tuning. You can't get application performance without database performance. Give everyone on the team a comprehensive view of how every aspect of the system affects performance across SQL database operations, host server and OS, virtualization resources and storage I/O. Quickly find bottlenecks and troubleshoot complex problems.
Between 2005 and 2020, data volumes will grow by a factor of 300 – enough data to stack CDs from the earth to the moon 162 times. This has come to be known as the ‘big data’ phenomenon. Unfortunately, traditional approaches to handling, storing and analyzing data aren’t adequate at this scale: they’re too costly, slow and physically cumbersome to keep up. Fortunately, in response a new breed of technology has emerged that is cheaper, faster and more scalable. Yet, in meeting these new needs they...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
In IT, we sometimes coin terms for things before we know exactly what they are and how they’ll be used. The resulting terms may capture a common set of aspirations and goals – as “cloud” did broadly for on-demand, self-service, and flexible computing. But such a term can also lump together diverse and even competing practices, technologies, and priorities to the point where important distinctions are glossed over and lost.
Monitoring of Docker environments is challenging. Why? Because each container typically runs a single process, has its own environment, utilizes virtual networks, or has various methods of managing storage. Traditional monitoring solutions take metrics from each server and applications they run. These servers and applications running on them are typically very static, with very long uptimes. Docker deployments are different: a set of containers may run many applications, all sharing the resource...
The 20th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held June 6-8, 2017, at the Javits Center in New York City, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Containers, Microservices 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 speaking proposal ...
You have great SaaS business app ideas. You want to turn your idea quickly into a functional and engaging proof of concept. You need to be able to modify it to meet customers' needs, and you need to deliver a complete and secure SaaS application. How could you achieve all the above and yet avoid unforeseen IT requirements that add unnecessary cost and complexity? You also want your app to be responsive in any device at any time. In his session at 19th Cloud Expo, Mark Allen, General Manager of...
In his session at 19th Cloud Expo, Claude Remillard, Principal Program Manager in Developer Division at Microsoft, contrasted how his team used config as code and immutable patterns for continuous delivery of microservices and apps to the cloud. He showed how the immutable patterns helps developers do away with most of the complexity of config as code-enabling scenarios such as rollback, zero downtime upgrades with far greater simplicity. He also demoed building immutable pipelines in the cloud ...
"Dice has been around for the last 20 years. We have been helping tech professionals find new jobs and career opportunities," explained Manish Dixit, VP of Product and Engineering at Dice, in this SYS-CON.tv interview at 19th Cloud Expo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
@DevOpsSummit taking place June 6-8, 2017 at Javits Center, New York City, is co-located with the 20th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. @DevOpsSummit at Cloud Expo New York Call for Papers is now open.
Rapid innovation, changing business landscapes, and new IT demands force businesses to make changes quickly. In the eyes of many, containers are at the brink of becoming a pervasive technology in enterprise IT to accelerate application delivery. In this presentation, attendees learned about the: The transformation of IT to a DevOps, microservices, and container-based architecture What are containers and how DevOps practices can operate in a container-based environment A demonstration of how ...
Cloud Expo, Inc. has announced today that Andi Mann returns to 'DevOps at Cloud Expo 2017' as Conference Chair The @DevOpsSummit at Cloud Expo will take place on June 6-8, 2017, at the Javits Center in New York City, NY. "DevOps is set to be one of the most profound disruptions to hit IT in decades," said Andi Mann. "It is a natural extension of cloud computing, and I have seen both firsthand and in independent research the fantastic results DevOps delivers. So I am excited to help the great t...
Without lifecycle traceability and visibility across the tool chain, stakeholders from Planning-to-Ops have limited insight and answers to who, what, when, why and how across the DevOps lifecycle. This impacts the ability to deliver high quality software at the needed velocity to drive positive business outcomes. In his general session at @DevOpsSummit at 19th Cloud Expo, Phil Hombledal, Solution Architect at CollabNet, discussed how customers are able to achieve a level of transparency that e...
Application transformation and DevOps practices are two sides of the same coin. Enterprises that want to capture value faster, need to deliver value faster – time value of money principle. To do that enterprises need to build cloud-native apps as microservices by empowering teams to build, ship, and run in production. In his session at @DevOpsSummit at 19th Cloud Expo, Neil Gehani, senior product manager at HPE, discussed what every business should plan for how to structure their teams to delive...
DevOps is being widely accepted (if not fully adopted) as essential in enterprise IT. But as Enterprise DevOps gains maturity, expands scope, and increases velocity, the need for data-driven decisions across teams becomes more acute. DevOps teams in any modern business must wrangle the ‘digital exhaust’ from the delivery toolchain, "pervasive" and "cognitive" computing, APIs and services, mobile devices and applications, the Internet of Things, and now even blockchain. In this power panel at @...