Hemmelig is a messing app with with client-side encryption and self-destructing messages. Prior to version 7.3.3, a Server-Side Request Forgery (SSRF) filter bypass vulnerability exists in the webhook URL validation of the Secret Requests feature. The application attempts to block internal/private IP addresses but can be bypassed using DNS rebinding or open redirect services. This allows an authenticated user to make the server initiate HTTP requests to internal network resources. Version 7.3.3 contains a patch for the issue.