SECURITY 101
How to Evaluate a Static Application Security Testing (SAST) Solution
November 13, 2023
Static Application Security Testing (SAST) is a foundational building block of an Application Security program. In this blog, we explore what qualities you should look for when selecting your SAST tools.
Static Application Security Testing (SAST) is a type of software testing that occurs relatively early in the software development lifecycle (SDLC). SAST scanners analyze an application's source code to detect syntax errors, bugs, and vulnerabilities, providing vital feedback to developers.
The static nature of SAST scans means the tool doesn't need to run your source code. It merely inspects the code within your files, ensuring tests are kept performant and portable. For this reason, SAST is often one of the first stages of testing in the development pipeline—discovering a security problem can cause the rest of the pipeline to be terminated early, preventing potentially vulnerable code from being called by later dynamic tests.
Adding SAST to your SDLC workflows allows you to spot and remove issues before they're included in production software. However, with a wide variety of SAST solutions available, it can be challenging to select the right one. In this article, we'll explain how to evaluate different options to select the best one for your project and team.
SAST scans provide developers with insights into the quality and security of code during the development process. SAST is used to enforce coding standards, prevent bugs that could cause unexpected runtime behavior, and identify potential misconfigurations and security risks.
Utilizing a SAST solution within your SDLC is one way to identify new code risks as they enter your project. Tools can surface problems before they are compiled into a finished binary or distributed to customers. Because code isn't executed by the scanning engine, SAST allows teams to identify threats that could compromise CI/CD or test servers, ensuring mitigation takes place before they can affect future pipeline stages.
Furthermore, SAST can help you achieve and maintain compliance with applicable regulatory standards such as ISO requirements, SOC2, HIPAA, and PCI DSS. Although SAST scans don’t produce an exhaustive picture of the risks facing your project—other security mechanisms, such as dynamic tests and supply chain hardening, are also required—you can use them to demonstrate the absence of certain coding issues that could affect a compliance audit's outcome.
The SAST arena has expanded considerably over the past few years. It includes developer-oriented tools that work with specific languages, tools that are engineered for security and risk-management scenarios, and generic scanning engines that can be integrated with many different project types.
To successfully adopt SAST, you need an accurate solution that can be easily added to your development process. SAST should empower developers with new and actionable information, instead of creating friction that leaves engineers waiting for results.
Here's how you can evaluate different SAST tools and providers so you can make the right choice first time.
SAST scans should be easy to deploy and integrate with your project. Tools that require complex configuration result in additional overheads and will require specialist knowledge to maintain over time.
Many solutions require you to manually configure new CI/CD pipeline stages before you can run scans and access their results. This increases set up time and can cause missing code coverage if administrators don't enable SAST for their projects.
Tools that support pipelineless execution offer a lower effort experience with automatic coverage for new repositories. They can simultaneously minimize the burden on administrators while delivering faster, more accurate results.
It goes without saying that whichever SAST solution you choose, it needs to support the languages and frameworks that you're using in your product. Some SAST tools only work with specific languages whereas others such as Semgrep use customizable rules to support many different languages.
If your stack depends on multiple languages or frameworks, you should consider one of these general-purpose tools to support standardization within your teams. This is also helpful when you need to work with legacy code that lacks dedicated language coverage from a purpose-built tool.
To ensure that all risks are discovered, you need to attain 100% coverage of all the code assets in your repositories. Tools capable of supporting every language that's used can therefore simplify report output and reduce overall pipeline execution time. It's also useful to look for tools that can list the files that were skipped due to exclusion rules or missing language coverage.
SAST is most effective when it's fast: scans should occur in real-time, as code is authored. Shifting SAST as far left in the development process as possible allows new errors and risks to be discovered before they have a chance to persist in your project.
Analyze the available tools to understand your options for accessing and distributing scan results. Results should be immediately made available to the individuals who need them—such as the developer who pushed a commit, or the security team that initiated a scheduled scan—so the SDLC feedback loop is kept tight and efficient. Any roadblocks in the way of developers will reduce productivity and discourage ongoing use of the SAST solution.
Beware that different scanning tools may impose requirements on the kinds of input they work with. Some solutions scan source files, whereas others analyze the output of compilation processes. This affects overall scan performance; tools that use compiled inputs will extend your pipeline's run time because compilation will have to occur before the scan can start.
Any SAST scanner you select should be focused on uncovering new findings that can be actioned to effect a quality or security improvement in your project. Scanners which don't help you prioritize and mitigate risks can lead to alert fatigue scenarios, where issues accumulate in your backlog because it's unclear which ones are actually relevant.
Look for cohesive SAST solutions that not only find issues, but which also explain why the problem has occurred and suggest an initial prioritization. This information should be provided directly within the SAST tool so that developers don't have to repeatedly cross multiple applications.
Users should be able to interact with SAST alerts and reports, such as by following links to view affected code in the repository, or apply a suggested mitigation. Tools that can't provide mitigations require developers to have pre-existing knowledge of the issue, why it presents a risk, and how it can be resolved. In cases where the developer is unfamiliar with the code, perhaps because they weren't the original author, this can impede the resolution process and lead to incorrect severity and priority assessments.
Similarly, SAST scans need to provide accurate risk context information so that developers, security leads, and project managers can efficiently determine the extent to which the product or organization is impacted. Alerts should include information such as the project the issue was found in, whether the scan ran against a production or development build, and the business importance of the repository. Other characteristics, such as the individual who introduced the issue and the developers best suited to resolving it, are also useful to expedite the resolution process.
These details help you efficiently triage issues and prioritize your backlog. Minor code quality issues within projects created for internal use are unlikely to require an immediate fix, for example, whereas vulnerabilities detected in your core product's repositories should be elevated to the top of the queue.
SAST isn't a "one-size fits all" category. Although you can get good results out-of-the-box, for long-term use you should seek customizable solutions like Semgrep that allow you to extend the scanning engine with your own rules and policies. This permits use of one SAST tool across your entire product catalog.
Being able to customize behavior on a per-project, per-repository, or per-team basis ensures different scenarios aren't unnecessarily encumbered by requirements held by the others. You can maintain a central ruleset that all code should adhere to, then layer in the specific customizations that apply to individual situations.
To support security teams and administrators in their work, SAST solutions should ideally provide enough information about their own usage to facilitate full visibility and oversight. Audit logs and usage analytics allow you to understand which teams and developers are effectively using scans, versus those which may need additional support to adopt SAST and start responding to risks.
These insights can reveal trends in the types of issues that are being discovered too. Recurring vulnerabilities, or repeated incidences of similar code quality problems, can indicate that teams need additional training so they can recognize and prevent those risks.
SAST scans should be automated, frequent, and comprehensive to provide maximum protection and ensure consistency throughout your entire SDLC.
A pipelineless approach provides advantages in this area, allowing you to easily set up scheduled scans that occur independently of code events such as merges and pushes. This provides continual coverage as SAST rules and vulnerability definitions change, even for projects that aren't regularly maintained. Only running scans as part of a pipeline could mean zero-day vulnerabilities go undetected until you next commit to your project.
As we've discussed above, the results of scans—whether triggered manually, on a schedule, or within a deployment pipeline—should be automatically distributed to relevant team members, ready for actions to be applied. Tools that can send automated alerts to IDEs, chat apps, or pull requests guarantee information is presented where devs will see it, with easy access to available mitigations.
SAST scans analyze code without running it to find bugs, misconfigurations, and vulnerabilities. This provides rapid feedback to developers, allowing issues to be fixed before they cause a problem in later testing stages or after deployment to users.
When choosing a SAST solution, you should balance factors such as scan performance, code coverage, customization, and the extent to which each tool helps you find, prioritize, and fix issues. SAST scans ideally supply actionable information that allows you to gauge the severity of each risk and understand how it can be resolved. This empowers you to improve application security and quality by ensuring relevant problems are dealt with before code gets deployed.
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