SAST and DAST are the two ways to test a mobile app's security, and they answer different questions. Static analysis (SAST) reads the app without running it and tells you what is inside, hardcoded secrets, insecure storage settings, weak crypto, an over-exposed binary. Dynamic analysis (DAST) runs the app and watches what it does, the actual network traffic, the runtime behavior, the auth flow in practice. Neither replaces the other, and knowing which catches what helps you decide where to start. Here is the difference and how they fit together for mobile.
Short answer
SAST (static application security testing) analyzes a mobile app without running it, examining the compiled binary or code to find issues like hardcoded secrets, insecure storage configuration, weak cryptography, and over-exposed components. DAST (dynamic application security testing) analyzes the app while it runs, observing real network traffic, runtime behavior, and how authentication and data handling actually work. Per OWASP MASTG, thorough mobile testing uses both, because they catch different things: static analysis finds what is in the build, and dynamic analysis finds how it behaves at runtime. A static pre-submission scan is the fast, broad first pass; dynamic and manual testing add the runtime depth.
What you should know
- SAST reads, DAST runs: static analyzes the build, dynamic analyzes execution.
- They catch different issues: in-the-binary versus at-runtime.
- SAST is fast and broad: no running app needed, good first pass.
- DAST needs execution: a running app, instrumentation, traffic capture.
- Use both: each covers a layer the other misses.
What is SAST for mobile?
Static analysis examines the app without executing it. For a mobile app, that usually means analyzing the compiled binary, the APK, AAB, or IPA, and sometimes the source, to find security issues in what is actually present: hardcoded secrets and keys, insecure data storage settings, weak or misused cryptography, exported components, cleartext network configuration, debuggable flags, and private or deprecated API references. Because it does not need the app running, SAST is fast and broad, can be automated, and can scan the exact artifact you are about to ship. Its limits are that it sees structure rather than behavior, so it can produce false positives and cannot observe what only happens at runtime. SAST answers the question "what is in this build that should not be."
What is DAST for mobile?
Dynamic analysis examines the app while it runs. For mobile, that means executing the app on a device or emulator and observing its behavior: the real network traffic it sends, whether it validates TLS certificates in practice, how its authentication and session handling behave, and how it responds to manipulated input or a tampered environment. DAST can catch issues that only appear in execution, such as an app that accepts an invalid certificate at runtime, leaks data over the network, or mishandles a session, which static analysis cannot fully see. The tradeoff is setup and scope: DAST needs a running app, often instrumentation and traffic interception, and it only exercises the paths you actually trigger. DAST answers the question "what does this app do when it runs."
SAST versus DAST: what each catches
The two are complementary, not competing. The table shows the split.
| Aspect | SAST (static) | DAST (dynamic) |
|---|---|---|
| How it works | Analyzes the build without running it | Runs the app and observes behavior |
| Catches | Hardcoded secrets, storage config, weak crypto, exposed components | Runtime traffic, TLS validation in practice, auth and session behavior |
| Speed and setup | Fast, broad, automatable | Slower, needs a running app and instrumentation |
| Blind spots | Runtime-only behavior | Code paths not exercised during the test |
| Best as | First pass on the exact artifact | Runtime depth and behavior verification |
The pattern is that static analysis is excellent at finding the concrete, in-the-binary issues that cause most mobile incidents, and is the natural first pass because it is fast and scans what you ship, while dynamic analysis verifies the behavior static cannot see. Using both gives coverage across the build and the runtime.
What to watch out for
The first trap is assuming one method is enough; SAST cannot see all runtime behavior, and DAST only exercises the paths you trigger, so relying on either alone leaves gaps. The second is running analysis on the source but not the artifact you ship, when the built binary is what matters. The third is treating either as a substitute for fixing the underlying design, since a scan finds issues but you still remediate them. A pre-submission scan such as PTKD.com (https://ptkd.com) is a static analysis that reads the compiled APK, AAB, or IPA against OWASP MASVS and surfaces the in-the-binary issues quickly, which is the efficient first pass; pair it with dynamic and manual testing for runtime coverage on higher-risk apps.
What to take away
- SAST analyzes a mobile app without running it, finding in-the-binary issues like hardcoded secrets, insecure storage, weak crypto, and exposed components.
- DAST runs the app and observes behavior, finding runtime issues like network traffic, TLS validation in practice, and authentication handling.
- They are complementary: static is the fast, broad first pass on the exact build, and dynamic adds runtime depth.
- Use a static pre-submission scan such as PTKD.com on the artifact you ship, and add dynamic and manual testing for runtime coverage where the risk warrants it.
