RASP can help with API attacks that show up as dangerous behavior inside the application, such as injection through a request parameter. It is much weaker against abuse that looks like normal use, such as someone legitimately calling an endpoint they should not have access to. Authorization and business logic need other controls.
What sits where
A WAF applies a set of rules to an HTTP conversation, aimed at common attacks like cross site scripting and SQL injection, per OWASP. It sits in front of the application as a reverse proxy would. A runtime agent sits inside the process and sees what the code does with the input. That inside view can tell a harmless string from one that reaches a database call unescaped. Both are generic descriptions, and products vary.
Where runtime protection helps for APIs
- Injection through query parameters, headers, or JSON fields, when the agent sees the dangerous call being made.
- Unexpected file or process activity triggered by a request.
- Known exploit patterns against a vulnerable component, as a temporary shield until you can fix it.
Where it struggles
| API problem | Why it is hard for a runtime agent |
|---|---|
| Broken object level authorization | The request is valid, the user is wrong |
| Excessive data exposure | The response is allowed, just too large |
| Business logic abuse | Each call looks normal, the sequence is the attack |
| Abuse of rate and cost | Needs volume analysis, not code inspection |
| Shadow and forgotten endpoints | The agent cannot protect what is not instrumented |
These problems are about intent and permission, not malformed input. They are solved with design: consistent authorization checks, tests that try other users' objects, response filtering, and rate limits.
How to cover the gaps
- Keep an inventory of every API, including old versions and internal ones.
- Write authorization tests that attempt access across users and tenants.
- Test the running API with a dynamic scan, and review the results with developers.
- Add rate limiting and monitoring at the gateway.
- Use runtime protection as one layer for injection style attacks, not the whole plan.
A worked example: an order lookup endpoint
An endpoint returns an order by identifier. A logged in user changes the identifier in the request to one belonging to another customer and receives that order. Every part of the request is well formed. No injection, no malformed input, and no known exploit pattern. A runtime agent watching for dangerous behavior sees an ordinary database lookup.
The fix is in design: check that the order belongs to the caller before returning it. The test is also simple: authenticate as one user and request another user's object, then assert that access is denied. This is the pattern for a whole class of API problems that need tests and code, not runtime filtering.
Layering controls for APIs
| Layer | Role |
|---|---|
| Design and code | Authorization checks, response filtering |
| Tests | Cross user and cross tenant access tests |
| Gateway | Authentication, rate limits, schema checks |
| Runtime agent or WAF | Injection and known exploit patterns |
| Monitoring | Unusual sequences and volume |
Each layer covers what the others miss.
Shadow endpoints
Runtime tools only protect what they instrument and see. Old versions, test endpoints left running, and internal APIs exposed by accident sit outside that coverage. Maintain an inventory built from several sources: code, gateway configuration, and traffic. Compare the lists regularly, and retire anything nobody can explain.
Testing authorization as a habit
Make authorization tests part of every new endpoint. Create two test users in different tenants, and for each endpoint try each user's credentials against the other's objects. Assert that access is denied and that error messages do not reveal whether an object exists. Add checks for fields that should never appear in responses. These tests are cheap to write and catch the class of flaws that runtime tools see poorly. They also document your intended access rules for future developers.
Summary table
| Attack type | Runtime agent | Better answer |
|---|---|---|
| Injection via parameter | Often helpful | Fix code, keep as extra layer |
| Known exploit of a library | Helpful as temporary shield | Upgrade the library |
| Object access across users | Weak | Authorization checks and tests |
| Data over exposure | Weak | Response filtering |
| Logic abuse | Weak | Design review and monitoring |
| Unknown endpoints | Cannot see | Inventory and retirement |
What to ask a vendor about APIs
Ask which API styles are supported, how requests are parsed, whether the agent understands your authentication model, and how it handles unknown or deprecated endpoints. Ask for examples of attacks it blocks and ones it explicitly does not. A candid answer about limits is a good sign.
Try it yourself
Click through it at your own pace, or open it full screen.
Notice the kinds of issues an API scan reports, and ask which of them a runtime agent could have blocked.
Questions for your API owners
Ask each API owner four things. Which endpoints exist, including old versions? Who is allowed to call each one? What happens if a user changes an identifier in the request? What is the maximum amount of data a single call can return? Their answers show where runtime protection will not help and where tests and design changes are needed. Keep the answers in a shared document and review them when endpoints are added.
Quick check
Does RASP replace an API gateway?
No. A gateway handles authentication, routing, and rate limits. RASP watches behavior inside the application.
Will RASP find business logic bugs?
Rarely. Those need design review and targeted tests.
Should I choose a WAF or RASP for my API?
They protect from different positions and can be combined. See the linked comparison, and weigh effort, ownership, and what each can see.
For where RASP fits with other controls, see WAF versus RASP. Safeguard's free scan at gold.safeguard.sh/scan covers dependency and SBOM risk behind your APIs.
Sources
Last reviewed: 19 October 2026.
