Semgrep: The Easiest SAST Tool For Developers (And Everyone Else)

If you’re not a seasoned static analysis expert, there’s a chance you’ve not even heard of this particular scan tool. But once you understand how it works, you’ll quickly find out why Semgrep—an open-source SAST tool the entire security industry is raving about these days—is worth all the hype.

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It all comes down to the way Semgrep scans for vulnerabilities in your code — it’s right there in the name. ‘Semgrep’ is portmanteau of ‘semantic’ and ‘grep’, signifying that the tool combines both abstract syntax trees (AST) and regular expressions (regex) to find specific flaws.

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How Semgrep combines semantics with regular expressions

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Many older SAST tools rely on regular expressions for finding vulnerable code — in other words, they looked for specific strings/patterns of code that were insecure. But not only is this slow, it also fails to take into account the syntax and structure of the code. Looking at code line by line may help you find some individual vulnerabilities, but it won’t help you trace back a vulnerability from sink back to the original source, or find broader insecure patterns.

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For that, your static analysis tool needs to analyse the syntax and semantics of your code; i.e., it needs to understand what your code means and how it’s interpreted, not just blindly read through each line.

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This is how Semgrep works: first, it parses your source code into an AST, understanding the code's structure and semantics beyond mere text patterns. The AST captures details like scopes, control flow, and syntactic constructs, giving you some seriously granular control. For example, you can use Semgrep to:

• Match function definitions and usages across various scopes.
• Identify variable declarations and their usages within different contexts.
• Detect specific API calls and their parameters.

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Next, it allows you to write your own custom rules to look for specific vulnerabilities using the AST structure, making it possible to narrow down your search and avoid false positives. You can even choose from a massive registry of rules made by the Semgrep team and the community.

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But here’s the cool part: Semgrep rules are easy for humans to read and write, and will look extremely familiar to someone who’s used grep commands or regular expressions. This makes it simple for even a beginner user to create custom rules without needing a deep knowledge of AST structures.

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Check out recorded webinar: “Leveraging SemGrep and Static Analysis for Paved Roads and Secure Defaults”.

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Why you should use Semgrep for SAST

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As a lightweight, easy-to-automate static analysis tool, Semgrep has a ton of benefits that almost no other tool can offer. Here’s some of its most powerful features:

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1. Supports 30+ languages
   
   Most static analysis tools that use AST to find vulnerabilities run up against the same problem: they lack support for multiple languages. They might support a handful of popular languages, but when you’re working on large software projects where multiple languages are in use, this limitation catches up to you fast.
   
   Semgrep even offers generic pattern matching for languages it doesn’t yet support, so it’s not like it’s unusable otherwise.
   
   
2. Flexible rules
   
   Not only does Semgrep let you write custom rules, but the ability to write rules that target specific AST nodes means it can be used for a wide range of checks, from simple stylistic rules to complex security vulnerabilities.
   
   
3. Developer-Friendly
   
   Semgrep’s rules are designed to be readable and writable by developers without needing deep expertise in static analysis. Its rules are easy to understand, and it integrates seamlessly into development workflows. You can use locally, in your CI/CD pipeline, or as part of your IDE.
   
   
4. Community-Driven
   
   Being open-source, Semgrep has steadily amassed a large and active community of users. They can share rules, contribute to the tool’s development, and collaborate on improving security and code quality across the industry.
   
   
5. Fast and lightweight
   
   Semgrep is designed to be fast and lightweight, making it suitable for use in CI/CD pipelines where speed is critical. It doesn’t require complex setup or heavyweight infrastructure.
   
   
6. Precision and context-awareness
   
   By using the AST, Semgrep avoids false positives and negatives that simple text searches might produce. It understands the code's structure, so it can differentiate between similar text patterns used in different contexts.

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How to learn automated static analysis with Semgrep

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If all this hasn’t convinced you that Semgrep is worth giving a try, maybe you need to see it in action first! There are a few ways to learn how to use Semgrep for SAST scanning, starting with an easy, free option.

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For a short exploration of Semgrep, you should check out our upcoming webinar: “Leveraging SemGrep and Static Analysis for Paved Roads and Secure Defaults”. Here, AppSecEngineer’s Chief Research Officer Abhay Bhargav looks at how SemGrep can help you establish secure coding practices and enforce policy compliance across your codebase.

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Over the course of 90 minutes, this live session will show you how to integrate static analysis seamlessly into your development workflow to enhance security and productivity. Tune in for this one on 27th June, at 9AM PT! 

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If you think you’re ready for the next step and want to get hands-on with Semgrep, you should check out this course: Static Analysis and Code Review for DevSecOps. This course is all about learning to automate SAST scans as part of your CI/CD pipeline using tools like Semgrep, Bandit, and more. You’ll get to run all these tools on real-world environments with our hands-on labs, so you’re in the driver’s seat the whole time!

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There are two ways you can get it: the AppSecEngineer Individual plan that gives you access to all courses on the platform, from cloud security, to DevSecOps, to AI and LLM security. You get hundreds of courses, labs, challenges, and playgrounds.

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For a more focused option, you can try out the DevSecOps Collection, which contains our full library of courses, labs, and challenges related to security automation, supply chain security, and CI/CD pipelines.

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Check out our recorded webinar: “Leveraging SemGrep and Static Analysis for Paved Roads and Secure Defaults”.

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