How DAST identifies zero-day and runtime vulnerabilities

Key takeaways

• Many runtime flaws and zero-day vulnerabilities evade static code scanners but can be exposed by DAST when testing a running application.
• Dynamic application security testing (DAST) uncovers real-time risks by analyzing live application behavior, not just source code.
• Invicti’s proof-based DAST automatically verifies many findings with safe proof-of-exploit to help teams focus on what matters, not false positives.
• For organizations serious about threat detection, DAST is essential for uncovering exploitable behavior in running applications.

The challenge of zero-day and runtime vulnerabilities

Some of the most dangerous security threats are also the hardest to detect. Zero-day vulnerabilities are flaws that:

• Haven’t been publicly disclosed
• Don’t have a patch
• May be under active exploitation (they don’t have to be, but this is often what drives response)

These aren’t theoretical risks but real attack vectors with no warning and high impact.

What makes them so elusive? They often don’t appear as clear-cut code errors detectable by static patterns. Instead, they emerge in dynamic application logic, environment-specific configurations, or unexpected interactions that only occur at runtime.

Similarly, runtime vulnerabilities include security flaws that:

• Depend on user sessions or authentication states
• Rely on server configuration, third-party plugins, or business logic
• Remain invisible to SAST/SCA tools that can’t emulate a live application’s behavior

In other words, you can’t catch what you can’t simulate, and static tools simply weren’t built to test how apps behave when they’re running. That’s why best practice is to always pair static analysis with runtime testing and to run DAST against non-production environments seeded with non-production data.

How DAST exposes real-time risk

Dynamic testing with DAST approaches security from the outside in, just like an attacker would. Instead of analyzing source code, it probes the live application and its running components to identify real, exploitable behavior.

Active testing of running applications

DAST scans the application in its deployed state, using a range of automated attack techniques:

• Injection attempts (including SQLi and XSS)
• Business logic abuse
• Session tampering
• Input fuzzing
• Parameter manipulation

Because it only interacts with the app over HTTP/HTTPS, DAST emulates real-world attacker behavior and uncovers issues that only surface during execution.

Detection without prior knowledge

Unlike tools that rely purely on known insecure code patterns or CVE databases, DAST doesn’t need to look at the source code to test an app for vulnerabilities. By sending crafted input and analyzing responses, it can expose previously unknown issues within known vulnerability classes as well as custom logic flaws. 

If the app reacts in an insecure way, revealing data, breaking flow, or exposing unauthorized resources, DAST flags the issue, even if it’s never been seen or reported before – which is often the case with new first-party code.

This makes DAST especially effective for:

• Detecting security bugs in first-party code
• Zero-day vulnerability detection
• Finding logic flaws

External attack surface coverage

DAST can scan both public and internal endpoints, revealing vulnerabilities exposed across:

• Login portals
• Forms and query strings
• APIs and microservices
• Running third-party components

It picks up issues missed by code review or hidden in deployed components, including runtime dependencies, making it a powerful tool for mapping and testing your real external attack surface.

Invicti’s edge in zero-day and runtime detection

Invicti extends the power of DAST with unique features that maximize runtime visibility and minimize false positives.

Proof-based scanning

For common vulnerability classes that can be safely exploited, Invicti provides vulnerability reports that are automatically confirmed and include a read-only proof of exploit or even (where technically possible) a proof of concept to safely reproduce the issue. This shows you that the vulnerability isn’t theoretical but very much real, exploitable, and actionable.

Teams can:

• Skip manual triage
• Focus on verified exploitable issues first
• Accelerate remediation with confidence

Authentication-aware scanning

Zero-days often lurk behind login portals, in admin interfaces, or inside user workflows. Invicti supports:

• Complex session handling
• Token-based access
• Multi-step authentication flows

This ensures scans penetrate protected areas of the application and detect vulnerabilities where they’re most likely to matter.

Business logic testing

Runtime issues are often tied to how users interact with the app, not just what the app is made of. Invicti can simulate these workflows and uncover flaws like:

• Broken access controls
• Privilege escalation
• Unvalidated redirects
• Parameter tampering

These are vulnerabilities static tools seldom catch, yet they’re among the most exploited in the real world. Detection for issues such as IDOR and broken access control is strongest when configured with multiple roles, as is possible on the Invicti Platform.

API support

Modern apps rely heavily on APIs, and their dynamic nature makes them fertile ground for zero-day exploits. Invicti supports API scanning of:

• REST APIs
• GraphQL endpoints
• JSON and XML payloads
• API authentication mechanisms

It tests these interfaces as an attacker would, validating inputs, observing outputs, and catching insecure logic in real time.

Examples of runtime-only vulnerabilities

Not all risks live in code. Here are examples of vulnerabilities that are often invisible to SAST/SCA tools but exposed by DAST:

Insecure direct object references (IDOR)

A user manually changes a URL parameter to access another user’s data, bypassing access control checks. Easy to exploit in production. Hard to spot in static analysis. Best results require multi-role test accounts and authenticated scans.

Authentication bypass via misconfiguration

An endpoint is accidentally excluded from authentication logic. It looks secure in code but is reachable at runtime without proper checks.

Input handling bugs

Some input handling vulnerabilities only appear at runtime when specific encodings or payloads are processed, which DAST uncovers through input variation and payload testing.

Each of these examples highlights a core truth: you can’t secure what you can’t simulate. For all these checks, the best practice is to run in controlled production-identical environments to avoid unintended side effects in live systems.

DAST-first strategy for real security

Invicti advocates a DAST-first approach because it reflects how attackers think and how applications fail in real-world use. Of course, DAST-first doesn’t mean DAST-only — you can and should pair DAST with static SCA and SAST to cover supply-chain exposure and unreachable code paths, using DAST to validate exploitability and prioritize real risk.

Instead of chasing theoretical bugs or hypothetical risk, a DAST-first strategy lets you:

• Focus on real, exploitable vulnerabilities
• Prioritize runtime behavior and business logic
• Validate findings with safe proof-of-exploit
• Integrate directly into DevSecOps pipelines for scalable protection

This means your teams can:

• Spend less time triaging false positives
• Catch critical risks early
• Deliver secure code faster
• Strengthen your defense against zero-days before they are exploited in production

Final thoughts: You can’t patch what you can’t see

Static tools find bugs in code. But real breaches happen in runtime, when applications interact with users, systems, and data under dynamic conditions. That’s where DAST excels.

With DAST on the Invicti Platform, you can discover runtime vulnerabilities that static tools miss, validate many common issues with proof, scan APIs, web apps, and complex flows with confidence, and stay ahead of zero-day threats before they become breach headlines.

Next steps

• Explore Invicti’s runtime vulnerability scanning capabilities
• Schedule a demo and see how proof-based DAST detects what others miss
• Build a security strategy that sees and stops real threats before they strike

FAQs: DAST and zero-day detection