A Tale of Two Security Tools
Application security testing has shifted from a last-minute, pre-release checkpoint to an ongoing part of development. Modern teams have access to a set of complementary tools that surface issues while code is still being written. Static application security testing (SAST) and software composition analysis (SCA) are two of the most widely adopted, but they address fundamentally different parts of the codebase.
SCA: Managing the Open Source Supply Chain
SCA tools scan the open source components your project depends on. They identify each third-party library in the codebase, then cross-reference it against databases of known vulnerabilities and licensing information. This tells you when a dependency has a security flaw that needs patching, or when it carries a license that requires attribution or triggers policy compliance.
Advanced SCA tools automate much of this management and provide detailed vulnerability context so developers can act quickly. Because they analyze dependency manifests and lockfiles rather than executing code, SCA scans can run at any point in the software development lifecycle (SDLC).
SAST: Auditing Your Own Source Code
SAST tools examine the code your team writes itself. They inspect source before compilation or execution, looking for patterns that match known vulnerability classes. This makes SAST suitable for early development stages—there is no need for a running application to perform the analysis. Results appear in real time as developers write, giving them immediate feedback and the chance to fix flaws before the code moves downstream.
| SCA | SAST |
| Addresses open source code | Addresses proprietary code |
| Fixes involve patching vulnerabilities | Fixes involve writing more secure code or addressing security weaknesses |
| Commonly has false negatives when a library is not known by a tool | Commonly has false positives where an issue is not in fact a security risk |
Where the Two Diverge
While both tools ship security feedback and integrate across the SDLC, they differ significantly in how remediation plays out and how they perform at scale.
Fixing the Problem
Remediation with SCA is usually straightforward: update the vulnerable library to the patched version. The fix lives in your dependency manifest, not in your logic. SAST findings, by contrast, require code changes. The tool flags the offending pattern and might offer guidance on how to rewrite it, but the recommendations can be complex and the responsibility for a correct fix rests with the developer.
Speed and Noise
SCA tools are designed to be fast. Scans typically complete in seconds and do not add meaningful overhead to a build regardless of project size. Their main blind spot is false negatives: if a library is not indexed in the vulnerability database, the tool will not flag it. Traditional SAST solutions process entire source trees and were built when testing happened outside the normal workflow, which makes them comparatively slow. SAST engines that run inside the SDLC, like GitHub's code scanning, cut that latency considerably by analyzing code as it is pushed.
The Practical Pairing
Neither tool is a substitute for the other. SCA secures the supply chain of external code you bring in; SAST secures the proprietary logic you build on top of it. A mature security practice uses both, and the most effective point of collaboration is often the pull request, where dependency updates and source code changes are reviewed together.
On GitHub, these two capabilities map directly to Dependabot and code scanning. Dependabot watches your dependency tree continuously and alerts you to known vulnerabilities. Enabling Dependabot security updates goes further by automatically opening pull requests that apply the fix. Code scanning evaluates every push for new security flaws using the CodeQL engine, which draws on more than 2,000 open-sourced query rules from the GitHub Security Lab and external researchers. Results appear inline in the pull request, keeping security review alongside the code review.
Dependabot catches dependencies in real time, allowing you to understand:
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Neither tool eliminates the other, and a complete security story usually requires both. SCA gives you fast, reliable coverage of your open source dependencies, while SAST—especially when embedded in the dev workflow rather than bolted on late—brings similarly prompt feedback to the code your team actually writes.
