For Security professionals, choosing the right approach to application security testing is crucial. This blog post navigates the differences between two popular methodologies: Software Composition Analysis (SCA) and Static Application Security Testing (SAST). This post compares features, benefits, and when to leverage each approach for a robust security strategy.

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Introduction to SCA and SAST

Fundamentally, SCA and SAST are both application security testing tools. What type of code they scan, however, differs. SCA scans open source and other third-party dependencies for known vulnerabilities and license compliance issues. SAST scans proprietary code (code written in-house) for common coding mistakes such as cross-site scripting (XSS) or SQL injection errors.

Benefits of SCA for Security Professionals

Open source libraries comprise 80-90% of the code in modern software applications. The need has never been greater for software security teams to understand all the components and dependencies that make up their code base. SCA scans to create an inventory of open source components then compares those results against known vulnerabilities from databases like the National Vulnerability Database (NVD) as well as other sources. SCA solutions prioritize vulnerabilities by using metrics such as CVSS score, reachability, and business risk. Remediation advice is also provided. Typically, an SCA solution identifies the next version of an open source library that contains the fix. 

SCA identifies vulnerabilities in widely used components and open source libraries. SCA allows dev teams to develop faster by using open source components, yet still stay secure by understanding whether a specific component is free from known defects. Advanced SCA solutions can also tell you where vulnerable code has been deployed in production as well as identify pipeline dependencies like GitHub Actions or GitLab runners that have known vulnerabilities. Most SCA solutions can also generate a software bill of materials (SBOM), which is a list of ingredients that identifies all the components, libraries, tools, and processes used to develop, build, and publish software.

Benefits of SAST for Security Professionals

SAST analyzes proprietary source code for common weaknesses that make your application susceptible to attack like those listed in the OWASP Top 10. With SAST, scanning occurs early in the software development lifecycle (SDLC), generally during or just after development. SAST tools provide real-time feedback to developers, pinpointing the exact location in code of the suspected flaw. When a security flaw is identified, developers fix the code by rewriting it, remediating the issue before it is merged into the main branch of your code base.

Key Differences: SCA vs SAST

SCA focuses on known vulnerabilities in open source code that have been publicly disclosed. It looks at code that has been developed outside your organization. When a vulnerability is found, SCA does not patch the code but rather recommends a fix to a newer version of that open source library in which the vulnerability has been remediated. Because open source vulnerabilities are publicly disclosed, attackers are given a blueprint for exploiting these weaknesses. Any organization that uses open source components needs to be up to date with their open source dependencies.

On the other hand, SAST evaluates the source code, bytecode, or binary code of an application for vulnerabilities without the need for execution—think of it like proofreading a book for errors before it is published. SAST looks at code from the inside to prevent zero-day vulnerabilities, security flaws not yet known to the software vendor. This means that SAST can detect these important vulnerabilities before they become an issue.

One can put it this way: SCA focuses on open source libraries and third-party components from the outside, while SAST looks at proprietary source code from the inside. SCA checks for known vulnerabilities by comparing them to external databases, and SAST checks software at the code-level against a set of rules. Because of this, SCA is ideal for addressing vulnerabilities in third-party dependencies, even complex ones, while SAST is good for informing decision-making and remediating issues of code developed in-house.

Also Read: Secure Development Best Practices: Building Resilient Software Applications

Achieving Comprehensive Security: The SCA and SAST Combination

Of course, development teams don’t have to choose between one or the other. SCA and SAST are complementary technologies. An approach that incorporates both methodologies delivers the most robust application security. Together, SCA and SAST offer a comprehensive strategy for identifying and mitigating software vulnerabilities. While SCA detects known vulnerabilities in open source and third-party libraries, SAST delves deeper into the codebase to find potential coding flaws, including those that might be new or unknown. SCA and SAST can both be embedded into development workflows and provide continuous testing for comprehensive security across the SDLC. 

SAST covers the code your organization writes to make sure it is analyzed for security. SCA is used for any open source software that you use in the application. When done correctly, SAST and SCA identify security issues from both the inside and outside early in the SDLC. 

Think of it as an automotive manufacturer that builds some components but also imports specialized parts for a vehicle it assembles. SCA is like knowing exactly where the specialized parts came from, who made them, and whether any known issues exist. If there’s a recall of a part, you can quickly identify and replace that part with a newer, safer version. SAST is like an internal QA check of the parts you manufacture or build directly. With both methodologies in place, you can achieve comprehensive automotive reliability (security) regardless of where each individual part came from.

Complementary Technologies: Using Both SCA and SAST for Robust Security

There is room for both SCA and SAST in the modern application security testing landscape. Without a comprehensive approach to AppSec that includes both these solutions, your code isn’t covered and your organization risks exposure.

Cycode can help secure the software supply chain, not just from malicious third-party attacks, but also from potential insider threats, code tampering, and other vulnerabilities. Learn more here, or schedule a time to talk to a cybersecurity expert.

Further Reading: 5 Steps to Overcome AppSec Chaos with a Complete ASPM Platform

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