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SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+We only provide security updates for the latest version of the project. Please make sure you are using the latest version before reporting any issues.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| Latest  | :white_check_mark:  |
+| Older   | :x:                |
+
+## Reporting a Vulnerability
+
+If you discover a security vulnerability, please follow the steps below:
+
+1. Go to the repository's [Security Advisories](https://github.com/masutaka/github-nippou/security/advisories) page.
+2. Click on **"New draft security advisory"**.
+3. Provide as much detail as possible about the vulnerability, including the steps to reproduce the issue.
+
+Please do not open a public issue for the vulnerability. All vulnerabilities reported through Security Advisories will be reviewed and addressed as soon as possible.
+
+## Preferred Languages
+
+We prefer all security reports to be in **Japanese** or **English**.
+
+## Response Time
+
+You can expect a response within a few days.
+
+## Security Updates
+
+Once a security fix is available, we will release a new version and notify users via the repository's release notes.
+
+## Contact
+
+If you have any questions or need further assistance, please contact [masutaka.net@gmail.com](mailto:masutaka.net@gmail.com).