GitHub Security Alert: Merchant Webhook SSRF Vulnerability Exposes Internal Server Port Scanning

A critical Server-Side Request Forgery (SSRF) vulnerability has been identified in a GitHub repository's webhook system. The flaw allows a merchant to specify a webhook URL pointing to `127.0.0.1` or other loopback addresses, which could force the application's API to perform port scans against its own server instance. This creates a direct path for internal network reconnaissance and potential further exploitation from within the application's trusted environment.

The security issue, tagged with a 'Medium' complexity rating of 150 points, centers on the lack of validation for webhook endpoints. The system currently accepts URLs that target private networks and internal IP schemes, including `localhost` and `0.0.0.0`. The resolution requires implementing security regex patterns to actively block these addresses, ensuring the application fails fast when such configurations are detected, thereby preventing the forced internal requests.

This vulnerability underscores a significant oversight in input sanitization for externally controllable URLs that trigger backend calls. The exposure of internal services to port scanning via a merchant-controlled parameter represents a tangible security risk for any deployment of this codebase, necessitating immediate review and patching to segment external inputs from internal network targets.