This post is focused on security testing your code and container, and verifying that both conform to security and operational practices. One of the major advances over the last year or so is the introduction of security features for the software supply chain, from both Docker itself and a handful of third-party vendors. All the solutions focus on slightly different threats to container construction, with Docker providing tools to certify that containers have made it through your process, while third-party tools are focused on vetting the container contents. So Docker provides things like process controls, digital signing services to verify chain of custody, and creation of a Bill of Materials based on known trusted libraries. In contrast, third-party tools to harden container inputs, analyze resource usage, perform static code analysis, analyze the composition of libraries, and check against known malware signatures; they can then perform granular policy-based container delivery based on the results. You will need a combination of both, so we will go into a bit more detail:
Container Validation and Security Testing
- Runtime User Credentials: We could go into great detail here about runtime user credentials, but will focus on the most important thing: Don’t run the container processes as
root, as that provides attackers access to attack other containers or the Docker engine. If you get that right you’re halfway home for IAM. We recommend using specific user accounts with restricted permissions for each class of container. We do understand that roles and permissions change over time, which requires some work to keep permission maps up to date, but this provides a failsafe when developers change runtime functions and resource usage.
- Security Unit Tests: Unit tests are a great way to run focused test cases against specific modules of code – typically created as your dev teams find security and other bugs – without needing to build the entire product every time. This can cover things such as XSS and SQLi testing of known attacks against test systems. Additionally, the body of tests grows over time, providing a regression testbed to ensure that vulnerabilities do not creep back in. During our research, we were surprised to learn that many teams run unit security tests from Jenkins. Even though most are moving to microservices, fully supported by containers, they find it easier to run these tests earlier in the cycle. We recommend unit tests somewhere in the build process to help validate the code in containers is secure.
- Code Analysis: A number of third-party products perform automated binary and white box testing, failing the build if critical issues are discovered. We recommend you implement code scans to determine if the code you build into a container is secure. Many newer tools have full RESTful API integration within the software delivery pipeline. These tests usually take a bit longer to run, but still fit within a CI/CD deployment framework.
- Composition Analysis: A useful technique is to check library and supporting code against the CVE (Common Vulnerabilities and Exposures) database to determine whether you are using vulnerable code. Docker and a number of third parties provide tools for checking common libraries against the CVE database, and they can be integrated into your build pipeline. Developers are not typically security experts, and new vulnerabilities are discovered in common tools weekly, so an independent checker to validate components of your container stack is essential.
- Resource Usage Analysis: What resources does the container use? What external systems and utilities does it depend upon? To manage the scope of what containers can access, third-party tools can monitor runtime access to environment resources both inside and outside the container. Basically, usage analysis is an automated review of resource requirements. These metrics are helpful in a number of ways – especially for firms moving from a monolithic to a microservices architecture. Stated another way, this helps developers understand what references they can remove from their code, and helps Operations narrow down roles and access privileges.
- Hardening: Over and above making sure what you use is free of known vulnerabilities, there are other tricks for securing applications before deployment. One is to check the contents of the container and remove items that are unused or unnecessary, reducing attack surface. Don’t leave hard-coded passwords, keys, or other sensitive items in the container – even though this makes things easy for you, it makes them much easier for attackers. Some firms use manual scans for this, while others leverage tools to automate scanning.
- App Signing and Chain of Custody: As mentioned earlier, automated builds include many steps and small tests, each of which validates that some action was taken to prove code or container security. You want to ensure that the entire process was followed, and that somewhere along the way some well-intentioned developer did not subvert the process by sending along untested code. Docker now provides the means to sign code segments at different phases of the development process, and tools to validate the signature chain. While the code should be checked prior to being placed into a registry or container library, the work of signing images and containers happens during build. You will need to create specific keys for each phase of the build, sign code snippets on test completion but before the code is sent onto the next step in the process, and – most importantly – keep these keys secured so an attacker cannot create their own code signature. This gives you some guarantee that the vetting process proceeded as intended.