CORS Checker for Security
Test Access-Control-Allow-Origin headers, wildcard origin risks, and credentialed cross-origin exposure on any URL — free Quick Check, no signup.
What This Tool Checks
- Origin reflection detection
- Credentialed CORS risk analysis
- Allowlist-first policy fixes
Why It Matters
CORS problems are easy to miss because applications may seem to work normally while still allowing wildcard or reflected-origin behavior that weakens data isolation.
Best For
Best for teams shipping APIs, dashboards, and browser apps that rely on cross-origin requests, credentials, or mixed frontend/backend hosting models.
What To Do Next
Use the findings to confirm whether you need a tighter allowlist, safer credential handling, or a broader review of origin behavior across environments.
Related Resources
Frequently Asked Questions
What is a CORS checker and why do I need one?
A CORS checker inspects cross-origin response headers such as Access-Control-Allow-Origin and Access-Control-Allow-Credentials to determine whether browsers can expose your API or page data to untrusted origins. You need one to catch misconfigurations before attackers exploit them — overly permissive CORS policies are one of the most common web security weaknesses.
Is this CORS checker free?
Yes. Quick Check is free and works without creating an account. Enter a URL to review CORS policy behavior on the public response instantly.
How do I fix CORS issues?
Replace wildcard origins with explicit allowlists of trusted domains, avoid reflecting the incoming Origin header without validation, and separate credentialed endpoints from public ones. After each change, retest preflight and simple requests. See our step-by-step CORS fix guide for Express, Nginx, and Apache examples.
How do I use a CORS checker online?
Paste the HTTPS URL of your API or web endpoint, choose Quick Check mode, and submit. Vulnify reads the live response headers and reports wildcard origins, reflected-origin behavior, credential exposure, and preflight handling — no account required.
Where can I find a CORS security guide?
Vulnify publishes a CORS security guide at /tools/guides/cors-checker covering allowlist design, preflight troubleshooting, and staged rollout. Pair it with the fix guide at /fix/fix-cors-misconfiguration for remediation steps after your check.
What is a cross-origin requests tool?
A cross-origin requests tool evaluates how your server responds when browsers send requests from a different origin. It tests Access-Control-Allow-Origin, Access-Control-Allow-Credentials, and OPTIONS preflight behavior so you can confirm APIs only trust intended frontends.
What does Access-Control-Allow-Origin: * mean for security?
Setting Access-Control-Allow-Origin to * allows any website to read your server’s response. While acceptable for fully public resources, it becomes a critical risk when combined with Access-Control-Allow-Credentials: true — a combination that lets any origin trigger authenticated cross-origin reads of sensitive data.
What is the difference between simple and preflight CORS requests?
Simple CORS requests (GET, POST with standard content types) are sent directly and the browser checks the response headers afterward. Preflight requests use an HTTP OPTIONS method sent before the actual request to ask the server which origins, methods, and headers it permits. Preflight applies to requests with custom headers, non-standard methods like PUT or DELETE, or credentialed calls — and a misconfigured preflight response can silently block legitimate traffic or over-permit dangerous origins.
Does CORS affect cookies and sessions?
Yes. When Access-Control-Allow-Credentials is true, overly broad origin rules can let other sites trigger authenticated cross-origin reads. Tight origin allowlists are critical for API and dashboard endpoints.