Static Application Security Testing (SAST) Explained

What is SAST?

Static application security testing (SAST) is a key technique in proactive cybersecurity that involves automatically scanning source code for vulnerabilities before code execution. By detecting security vulnerabilities before code is deployed to production, SAST helps developers fix security risks, avoid costly errors, and enforce compliance. It uses automated tools to scan source code, bytecode, and sometimes even application binaries to detect potential code smells, security risks, or compliance issues.

The use of SAST embeds security measures early in the software development life cycle (SDLC). In this way, adopting SAST supports the shift-left security paradigm, where the focus on security is integrated early in the development process rather than addressed after deployment.

In this article, we’ll explore how SAST works, along with the types of vulnerabilities it can automatically detect.

How SAST works

SAST tools often integrate seamlessly with source code management tools such as Git, providing real-time feedback on errors and vulnerabilities found within the code so that developers can address them faster and earlier. When integrated into CI/CD pipelines, SAST shrinks the feedback loop by delivering continuous, automated security checks, helping teams enforce secure coding practices.

Static analysis of source code inspects it without executing it. SAST tools can scan an entire codebase—including dependencies, configuration files, and SQL queries—to detect potential vulnerabilities. The focus of SAST is to identify syntax issues, potential SQL injection vulnerabilities, cross-site scripting (XSS), and other non-standard or insecure coding practices.

Differences from dynamic application security testing (DAST)

SAST operates without a runtime environment, making it ideal for developers to receive early feedback on their code changes before the application is deployed to any environment. This is unlike dynamic application security testing (DAST), which tests the application during runtime to uncover vulnerabilities such as those listed in the OWASP Top Ten. DAST tools do not have access to the application's source codeand instead rely on simulated attacks to identify security weaknesses. For example, if a developer introduces a coding error that could lead to a buffer overflow, SAST can detect this flaw before the code reaches production.

SAST and DAST are complementary application security testing methods, together contributing to comprehensive coverage across different stages of the SDLC. By combining both approaches, development teams can ensure thorough security testing, capturing a wide range of vulnerabilities.

Types of vulnerabilities detected by SAST

A static scan of source code can help uncover a wide range of code quality and security issues before any code is executed. SAST tools enable teams to detect:

Code-based vulnerabilities

SAST uses lexical and semantic analysis to parse the entire source code, constructing an abstract syntax tree (AST) to examine the codebase and identify common patterns thoroughly. Lexical errors involve the structure or format of the code, such as unrecognized tokens, improperly formatted keywords, or illegal characters. These errors prevent the code from compiling or being parsed correctly. 

Semantic errors are issues related to the meaning or logic of the code. For example, when a program writes more data to a buffer than it can hold, it is a logical flaw in how memory is managed. While the code might be correct and might even compile, this error could introduce a buffer overflow at runtime. This analysis allows SAST to detect code-level security weaknesses that developers may not immediately notice but could result in crashes and insecure deserialization issues, which would allow attackers to execute arbitrary code.

SAST also identifies syntax errors—such as undeclared or mismatched variables, incorrect function calls, or incompatible data types—which could create unexpected and undesired behaviors.

Code quality issues

SAST tools are well equipped to catch code quality issues, including:

• Improper error handling
• Dead code
• Duplication issues
• Incorrect resource management

Alerting developers to these issues helps them write more secure and efficient code.

SAST tools also use pattern matching and rule-based analysis to identify hard-coded credentials, such as passwords or API keys, that attackers could exploit easily. Additionally, SAST can flag the use of outdated dependencies known to have security vulnerabilities, enabling teams to prioritize and fix them promptly. 

Security violations

SAST tools can check and notify developers about common security vulnerabilities, such as:

• XSS
• SQL injections
• Input sanitization
• Security misconfigurations

Most SAST tools also support custom configurations, allowing organizations to enforce internal security policies and ensure consistency across all codebases. 

SAST in the SDLC

One of the key advantages of SAST is how it seamlessly integrates with each step of the SDLC, ensuring security is an integral part of the development workflow. It allows developers to identify and mitigate issues while writing code, promoting a shift-left security approach. By embedding SAST into their development workflows, developers can iterate quickly and release code more confidently, ultimately reducing development costs.  

By integrating SAST tools with existing CI/CD pipelines, developers can perform automated and continuous scans in the build and release process. Static analysis usually runs significantly faster than runtime testing tools, making it possible to run checks more frequently. For example, teams can run these scans whenever a new commit is pushed to a branch or a pull request is opened. Additionally, many SAST tools can be set to scan only the proposed code changes in a pull request rather than the entire codebase. This allows teams to receive immediate feedback and to resolve issues faster.

CI/CD automation at every stage of the pipeline promotes secure coding practices and helps prevent security risks from reaching production environments. 

Challenges and limitations of SAST

SAST is a fast, cost-effective way to identify an application’s security issues before the code hits the production environment. However, it has some limitations.

• False positives: The techniques used by SAST tools to identify issues may occasionally yield false positives. Teams must review the identified issues to discard invalid or non-actionable issues before prioritizing real vulnerabilities.
• Complex issues: Some issues identified by SAST may require domain-specific expertise from security, infrastructure, or application development teams to understand the root cause and determine a fix. For example, SAST might identify the use of insecure cryptographic algorithms, such as MD5 or SHA1, but addressing the issue may require guidance from security teams to identify an alternative solution.
• Limited runtime visibility: SAST tools don’t have access to any environment-specific configurations. As a result, it can miss runtime issues, such as race conditions or security misconfigurations, that surface during application execution. Complementary testing with DAST can often assist in catching these vulnerabilities. Outside of application testing, many organizations rely on solutions like Falcon ASPM, which provide full visibility into risks associated with deployed applications. 
• Dependency limitations: SAST tools sometimes have difficulty identifying open-source dependencies. Organizations can overcome this limitation by using Software Composition Analysis (SCA).

Strengthen your application security with comprehensive coverage

SAST tools scan source code to detect issues before the code is deployed to any runtime environment. By identifying these vulnerabilities early in the SDLC, SAST helps developers address security concerns before code is released, thereby reducing development time and the risk of introducing vulnerabilities into production.

Because SAST cannot assess certain dependencies or access the execution environment, its abilities are limited. Therefore, SAST should be used alongside SCA, DAST, and ASPM to provide comprehensive security coverage, addressing static code-related vulnerabilities, dynamic runtime issues, and risks to applications in production. 

Ready to strengthen your application security? Discover how CrowdStrike Falcon ASPM can work alongside your SAST tools to provide comprehensive security coverage, reduce risks, and enhance your development workflow.