DAST vs SAST vs SCA vs secret scanning: which finds what

If you only run one kind of application security testing, you have a blind spot the size of whichever technique you skipped. The four main families — SAST, DAST, SCA, and secret scanning — are not competitors. They look at different artifacts, at different moments, and catch different classes of bug. Here is what each one actually does, where it fails, and why a serious program runs all four.

The one-paragraph version

Technique	Looks at	Catches	Misses
SAST	Your source code	Injection, unsafe APIs, logic flaws	Runtime/config issues, false positives high
DAST	The running app	Real exploitable behaviour, config	Anything not reachable at runtime
SCA	Dependencies	Known CVEs in libraries	Bugs in your code
Secrets	Code & history	Leaked keys, tokens, passwords	Logic and dependency issues

SAST — static analysis

Static Application Security Testing reads your source code without running it. It parses the code into a model and traces how untrusted data flows through your program — for example, from an HTTP parameter into a database query without sanitisation (SQL injection), or into a shell command (command injection).

• Strengths: Runs early (you can scan a pull request before it merges), sees code paths that are hard to reach at runtime, and points at the exact line.
• Weaknesses: It reasons about possible behaviour, so it is prone to false positives — it will flag a "vulnerable" pattern that is actually unreachable or already mitigated elsewhere. Tuning matters enormously.

SAST answers: is there dangerous code?

DAST — dynamic analysis

Dynamic Application Security Testing does the opposite: it ignores the source and attacks the running application from the outside, the way a real attacker would. It crawls endpoints, submits malicious payloads, and watches how the app responds.

• Strengths: Because it tests real behaviour, a DAST finding is usually a real finding — it actually reproduced the issue. It also catches things that only exist at runtime: misconfigurations, missing security headers, exposed admin panels, broken authentication.
• Weaknesses: It can only test what it can reach. Code behind a feature flag, a rarely-hit branch, or an un-crawled endpoint is invisible to it. It also runs later in the lifecycle, against a deployed environment.

DAST answers: can this actually be exploited right now?

SAST and DAST are the classic complementary pair — inside-out versus outside-in. A finding confirmed by both is about as real as it gets.

SCA — software composition analysis

Modern applications are mostly other people's code. Software Composition Analysis inventories your dependencies (direct and transitive) and checks them against vulnerability databases for known CVEs — plus, often, license compliance.

• Strengths: This is where a huge share of real-world risk lives. You did not write the vulnerable code, but you shipped it, and attackers scan for known-vulnerable library versions at internet scale. SCA is fast and high-signal.
• Weaknesses: It only knows about published vulnerabilities, and it tells you nothing about bugs in your own code. A clean SCA report is not a clean bill of health.

SCA answers: am I shipping someone else's known vulnerability?

Secret scanning

The simplest technique conceptually, and the source of some of the worst breaches. Secret scanning searches your code — and crucially its history — for credentials that should never have been committed: API keys, database passwords, private keys, cloud tokens.

• Strengths: Leaked credentials are immediately, trivially exploitable — no clever exploit chain required. Catching them (including in old commits, where they live forever once pushed) prevents a whole category of instant compromise.
• Weaknesses: Narrow by design. It finds secrets, not logic flaws or vulnerable dependencies. False positives (test fixtures, example keys) need handling.

Secret scanning answers: did we accidentally publish the keys to the kingdom?

Why you need all four

Each technique is defined as much by its blind spot as its strength:

• SAST sees code but not runtime.
• DAST sees runtime but not unreachable code.
• SCA sees dependencies but not your code.
• Secret scanning sees credentials but nothing else.

Run only SAST and you will drown in false positives while a leaked AWS key sits in your git history. Run only DAST and you will miss the vulnerable dependency that was never exercised by the crawler. There is no single technique whose blind spot the others do not cover — which is exactly why coverage means running all four.

The orchestration problem

Here is the catch: running four classes of tool produces four streams of output, in four formats, with overlapping and contradictory findings. The same underlying issue might be reported by two tools with two different severities, while the one finding that actually matters is buried on page nine.

This is the real work, and it is why simply owning the tools is not the same as having a security program. The value is in the layer on top: running the right tools against a verified target, correlating and de-duplicating their output into single findings, and ranking by real exploitability so a developer sees a short, ordered list instead of a wall of noise.

That orchestration — plan, run, de-dupe, rank — is exactly what Opzyai does across DAST, SAST, SCA, and secret scanning, on the apps and repos you own. Four techniques, one ranked list, continuously.