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SECURITY.md

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+# Security Policy
+
+## Reporting a Vulnerability
+
+To report a vulnerability, please privately report it via the Security tab on the correct GitHub repository ([see documentation](https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing-information-about-vulnerabilities/privately-reporting-a-security-vulnerability#privately-reporting-a-security-vulnerability)). Do not open a public issue. Provide:
+
+- A clear description of the issue
+- Steps to reproduce
+- Expected vs actual behavior
+- Potential impact
+- A proof of concept if possible
+- Affected commit / version (if known)
+
+## Acknowledgment Timeline
+
+We aim to acknowledge receipt of a valid report within 1 week.
+
+## Resolution Timeline
+
+We aim to provide a remediation plan or decision within 4 weeks. Actual fix time may be shorter or longer depending on severity, complexity, and scope.
+
+## Scope & Threat Model
+
+In scope:
+
+- Vulnerabilities introduced by code in this repository
+- Supply-chain risks caused by how this repository consumes or distributes its own code (e.g. insecure Github Actions)
+
+Out of scope:
+
+- Issues only present in third-party dependencies (please report those upstream)
+- Issues that can only be exploited when the underlying platform (browser, server runtime) is compromised
+- Denial of service via excessive legitimate use
+
+### Supported Versions
+
+The following versions are currently supported with security updates:
+
+| Package        | Version | Supported              |
+| -------------- | ------- | ---------------------  |
+| @xyflow/react  | 12.x    | ✅ Fully supported     |
+| @xyflow/svelte | 1.x     | ✅ Fully supported     |
+| @xyflow/system | 0.x     | ✅ Fully supported     |
+| reactflow      | > 11.x  | ⚠ Depends on severity  |
+| reactflow      | < 11.x  | ❌ No longer           |
+
+## Disclosure
+
+Please keep reports private until a fix is released and a Security Advisory is public.