Threat Detection in gVisor

By Fabricio Voznika on 31 August 2022

gVisor helps users secure their infrastructure by running containers in a dedicated kernel that is isolated from the host. But wouldn’t it be nice if you could tell when someone attempts to break out? Or get an early warning that your web server might have been compromised? Now you can do it with gVisor! We are pleased to announce support for runtime monitoring. Runtime monitoring provides the ability for an external process to observe application behavior and detect threats at runtime. Using this mechanism, gVisor users can watch actions performed by the container and generate alerts when something unexpected occurs.

A monitoring process can connect to the gVisor sandbox and receive a stream of actions that the application is performing. The monitoring process decides what actions are allowed and what steps to take based on policies for the given application. gVisor communicates with the monitoring process via a simple protocol based on Protocol Buffers, which is the basis for gRPC and is well supported in several languages. The monitoring process runs isolated from the application inside the sandbox for security reasons, and can be shared among all sandboxes running on the same machine to save resources. Trace points can be individually configured when creating a tracing session to capture only what’s needed.

Let’s go over a simple example of a web server that gets compromised while being monitored. The web server can execute files from /bin, read files from /etc and /html directories, create files under /tmp, etc. All these actions are reported to a monitoring process which analyzes them and deems them normal application behavior. Now suppose that an attacker takes control over the web server and starts executing code inside the container. The attacker writes a script under /tmp and, in an attempt to make it executable, runs chmod u+x /tmp/ The monitoring process determines that making a file executable is not expected in the normal web server execution and raises an alert to the security team for investigation. Additionally, it can also decide to kill the container and stop the attacker from making more progress.


Falco is an Open Source Cloud Native Security monitor that detects threats at runtime by observing the behavior of your applications and containers. Falco supports monitoring applications running inside gVisor. All the Falco rules and tooling work seamlessly with gVisor. You can use this tutorial to learn how to configure Falco and gVisor together. More information can be found on the Falco blog.

What’s next?

We’re looking for more projects to take advantage of the runtime monitoring system and the visibility that it provides into the sandbox. There are a few unique capabilities provided by the system that makes it easy to monitor applications inside gVisor, like resolving file descriptors to full paths, providing container ID with traces, separating processes that were exec’ed into the container, internal procfs state access, and many more.

If you would like to explore it further, there is a design document and documentation with more details about the configuration and communication protocol. In addition, the tutorial using Falco is a great way to see it in action.

We would like to thank Luca Guerra, Lorenzo Susini, and the Falco team for their support while building this feature.