SAST vs DAST vs IAST: What Each Finds and Misses

SAST reads your source code without running it. DAST attacks the running application from the outside. IAST puts a sensor inside the running application and watches what the code does while something else exercises it. RASP is not a test at all: it sits inside the application in production and blocks attacks. Each one sees a different slice of the problem. None of them knows what your application is for, so none of them can tell when one customer reads another customer’s data. That is the job of a manual code review or a penetration test.

SAST vs DAST vs IAST vs RASP at a glance

Method	What it examines	When it runs	Finds well	Misses
SAST	Source code or bytecode, not running	In the IDE, on each pull request, in CI	Injection paths, hard-coded secrets, unsafe functions, weak crypto calls, traced to the line	Runtime and deployment issues, configuration, authorization logic, flaws that span services
DAST	The running application, from outside, with no code	Against staging on each release candidate	Reachable injection, cross-site scripting, missing headers, weak TLS, exposed debug pages	Pages the crawler cannot reach, authorization between users, business logic, the line of code to fix
IAST	The running application, from inside, through an agent	In test or QA while functional tests or DAST drive traffic	Confirmed data flows from a request to a dangerous call, with the line of code	Code paths nobody exercised, unsupported languages, anything outside the instrumented app
RASP	Live requests in production, through an agent	Always on, in production	Blocks some exploit attempts as they execute	Finds nothing for you to fix; it is a protection layer, not a test
Manual review and penetration test	The code and the running application, by a person with context	Before major releases and at least annually	Authorization across roles and tenants, business logic, chained flaws, proof of impact	Breadth on every build; it is periodic, not continuous

The short version: run SAST and DAST automatically, add IAST if your stack supports it, treat RASP as a safety net, and put a person on the parts of the application where a mistake costs money or data.

SAST: reading the code without running it

Static application security testing parses your code and follows data from where it enters (a request parameter, a file, a message) to where it could do damage (a database query, a shell command, an HTML page). If untrusted input reaches a dangerous call without validation or encoding, the tool flags it and points to the file and line.

That is its big advantage. SAST runs early, on every pull request, before anything is deployed. A developer sees the finding while the code is still fresh, and the fix costs minutes.

Where it struggles:

• Noise. SAST reasons about code it cannot run, so it reports paths that look dangerous but are not reachable, or are already sanitized somewhere it cannot see. Untuned, it buries teams in findings. Most teams end up blocking builds only on a small set of high-confidence rules.
• Language and framework coverage. Support varies by language, framework and version. A tool that is strong on one stack can be blind to how another framework routes requests or handles templates. Check your stack before you buy.
• Anything decided at runtime. Server configuration, headers, TLS, cloud permissions and the way services talk to each other are not in the source file it is reading.
• Authorization logic. SAST can see that a handler loads a record by ID. It cannot know that the record belongs to someone else.

Software composition analysis (SCA), which checks your open source dependencies against known vulnerabilities, is often sold in the same product. It is useful and it is a different thing: SCA tells you a library has a known flaw, SAST tells you your own code has one.

DAST: attacking the running application from outside

Dynamic application security testing points a scanner at a deployed application, usually in staging. It crawls pages, forms and API endpoints, sends known attack payloads to every input it finds, and reads the responses for signs of success. It needs no source code, which makes it easy to add to any pipeline.

DAST is good at the flaws that show up in a response: injection it can reach, cross-site scripting, missing security headers, weak TLS, verbose errors and exposed debug endpoints. It is repeatable, so it catches the injection point a refactor quietly reintroduced.

It runs later than SAST because it needs a working build, and a full scan can take hours. It only tests what the crawler can reach, and complex logins or heavily scripted front ends can leave large parts of the application untested without any warning. When it does find something, it reports a URL and a parameter, not the line of code. We cover what DAST catches and misses in detail in DAST vs penetration testing.

IAST: a sensor inside the running application

Interactive application security testing installs an agent in the application runtime in a test environment. While your functional tests, your QA team or a DAST scan drive traffic through the application, the agent watches the code execute. When a request’s data actually reaches a dangerous call without being made safe, it reports the request and the line of code together.

Because it watches real execution, IAST reports fewer paths that are only theoretically dangerous than SAST does. It gives developers both halves of the story: the request that triggered it and the code to change.

The limits are practical. IAST only sees the code paths something exercised, so its coverage is as good as your tests. Agents exist only for certain languages and runtimes. And it adds an agent to your test environment, which some teams cannot or will not do.

RASP: protection, not testing

Runtime application self-protection uses a similar agent, but in production, and its job is to block rather than report. When an attack such as an injection attempt reaches a dangerous call, RASP can stop it. Think of it as a web application firewall that lives inside the application and can see the code.

RASP is worth knowing because it appears in every “SAST DAST IAST RASP” comparison. It does not find flaws for you to fix. It can buy time while a fix ships, and it should never be the reason a known flaw stays open.

What none of the tools find

Every method above works from patterns. The flaws that cause the worst application breaches are not patterns; they are specific to how your product works.

• Authorization across users and tenants. User A changes an ID in a request and reads user B’s invoice. Every tool sees a valid response.
• Business logic. Applying a discount twice, skipping a payment step, approving your own request, ordering a negative quantity.
• Authentication design. A reset token that can be predicted, or MFA that can be skipped by calling the next step directly.
• Chained findings. Three low-severity issues that together give an attacker the admin panel.

Finding these takes a person who knows what the application is supposed to do. There are two ways to buy that person’s time.

Where manual secure code review fits

A secure code review puts a reviewer on the code itself. At Invadel, AI-assisted static analysis triages the codebase first, then senior reviewers verify every finding by hand and read the code paths that matter most: authentication, access control, payments, file handling and anything that touches tenant data. Findings are traced to the exact line, with a fix that fits your framework.

It suits teams that want flaws found before release, products where the code is the fastest way to understand the access model, and teams that already run SAST and want a person to separate the real findings from the noise. Secure code review starts at $4,800 for a focused codebase, fixed in writing before work begins, with a free re-review once the fixes merge. Every tier is on the code review pricing page.

Where a penetration test fits

A web application penetration test attacks the running product the way an adversary would, with accounts in every role and a second tenant where the product is multi-tenant. It proves impact: the request, the response, and the data an attacker reached. It is also the document SOC 2 auditors, PCI DSS assessors and enterprise customers ask for. A SAST or DAST report does not replace it.

Web application testing starts at $5,200 and API testing at $4,000, each at a fixed price with a free retest. Code review and a penetration test are complementary: the review finds the flaw in the code, the test proves what it lets an attacker do.

How to layer them in a pipeline

1. Every pull request: SAST and dependency scanning, with builds blocked only on high-confidence rules so developers keep trusting the results.
2. Every release candidate: DAST against staging, or IAST if your stack supports it and your tests cover the application well.
3. Before a major release: a manual review of the code that handles identity, money and tenant data.
4. At least annually and after major changes: a penetration test. Hand the tester your scan output so the manual hours go to authorization and logic rather than to confirming what the tools already found.
5. In production, if you need it: RASP or a web application firewall as a compensating control while fixes ship.

This is the same idea as the layered approach in our web application security testing guide and shifting security left: cheap automated checks early and often, expensive human attention where it counts. The pipeline that runs these checks needs protecting as well: its runners, secrets and third-party actions are an attack path of their own, covered in our guide to CI/CD pipeline security.

Frequently asked questions

Is DAST better than SAST? Neither is better. SAST finds flaws in code before it runs and points to the line. DAST finds flaws in the running application that only show up at runtime. Most teams run both.

What is the difference between IAST and DAST? DAST attacks from outside and judges success from the response. IAST sits inside the application and watches the code execute, so it can confirm a flaw and name the line. IAST often uses DAST or functional tests to generate the traffic it watches.

What is the difference between IAST and RASP? Both use an agent inside the application. IAST runs in testing and reports flaws. RASP runs in production and blocks attacks.

Can SAST replace a manual code review? No. SAST finds pattern-based flaws and produces noise that someone has to triage. A reviewer verifies the real findings and reads the access-control and business logic that no rule describes.

Will an auditor accept a SAST or DAST report as a penetration test? Usually not. SOC 2 auditors, PCI DSS assessors and enterprise security reviews ask for a penetration test by an independent tester. Tool output is supporting evidence of a vulnerability management process, not a substitute.

What does a secure code review cost? At Invadel it starts at $4,800 for a focused codebase, fixed before work begins, with a free re-review once the fixes merge.

Fixed price, fixed scope, free retest. Code review from $4,800, web application testing from $5,200. Scope your test and get a written price within one business day.