SAST (static application security testing) analyses the code your team wrote, without running it, to find flaws such as injection. SCA (software composition analysis) inventories the open source libraries you use and checks them against known vulnerabilities and licenses. They find different problems, so most teams need both.
What does SAST look at?
Your own source code. OWASP describes static code analysis as running tools that try to highlight possible vulnerabilities within static, non-running source code using techniques such as taint analysis and data flow analysis. Taint analysis follows untrusted input, such as a form field, to see whether it reaches a dangerous operation, such as a database query, without being checked.
OWASP is candid about limits. It says ideal tools would find flaws automatically with high confidence, but that is beyond the state of the art for many types of flaw, so tools often serve as an aid that helps an analyst zero in on relevant code. Expect false positives and plan time for triage.
What does SCA look at?
The code you did not write. OWASP Dependency-Check describes itself as a software composition analysis tool suite that identifies project dependencies and checks if there are any known, publicly disclosed vulnerabilities. The idea traces to the OWASP Top 10 2013 entry on using components with known vulnerabilities.
SCA reads manifests and lock files, builds a list of direct and transitive dependencies, and matches versions against vulnerability databases. The same inventory supports a software bill of materials, and many programmes use it for license review too.
Where do they differ?
SAST answers: did we write something unsafe? Its findings point at a line in your repository, and you fix them by changing your code.
SCA answers: did we pull in something known to be unsafe? Its findings point at a package version, and you fix them by upgrading, replacing or removing it.
SAST can find a flaw nobody has ever reported, because it examines your logic. SCA can only report what has been disclosed, but it covers code that is often most of your application by volume.
What does a constructed example show?
A web service builds a report by concatenating a request parameter into a query string. SAST traces the parameter to the query and flags it. The same service also uses a year-old XML parsing library with a published flaw. SAST does not flag that, because the problem is inside the library. SCA does.
Fix one and you still have the other.
Why can SCA output be noisy?
A vulnerable library is not always a vulnerable application. If your code never calls the affected function, the risk is lower. This is why reachability analysis matters: it asks whether the vulnerable code path can actually be reached from your application. Safeguard offers reachability analysis alongside dependency scanning for this reason.
Where do they fit in the lifecycle?
NIST's Secure Software Development Framework (SP 800-218) describes practices such as reviewing and analysing code and verifying that acquired software meets security requirements. SAST fits the first, SCA the second. OWASP notes that running static analysis in the IDE gives developers immediate feedback, which is cheaper than finding problems later. SCA also belongs in the pull request and in release checks, and again on a schedule, since new vulnerabilities are disclosed against code you shipped last year.
How to check or apply this
- Confirm you have both: one tool that reads your source, one that reads your dependency manifests.
- Run SAST on pull requests, and set a policy for which severities block a merge.
- Run SCA on every build and nightly on your main branches.
- Generate an SBOM from the SCA inventory and keep it with each release.
- Triage SCA findings by exploitability and reachability, not raw count.
- Track time to fix for each, and review false positive rates quarterly.
Quick check
Can SCA replace SAST?
No. SCA checks third party packages for known issues. It does not examine the logic of your own code.
Does a vulnerable dependency always mean we are vulnerable?
No. It depends on whether your application reaches the vulnerable code. Reachability analysis helps decide.
Sources
- OWASP, Static Code Analysis
- OWASP Dependency-Check
- NIST SP 800-218, Secure Software Development Framework
- CISA, Software Bill of Materials
Last reviewed: 18 October 2026.
