Payload is a free and open source headless content management system. Prior to 3.75.0, a Server-Side Request Forgery (SSRF) vulnerability exists in Payload's external file upload functionality. When processing external URLs for file uploads, insufficient validation of HTTP redirects could allow an authenticated attacker to access internal network resources. The Payload environment must have at least one collection with `upload` enabled and a user who has `create` access to that upload-enabled collection in order to be vulnerable. An authenticated user with upload collection write permissions could potentially access internal services. Response content from internal services could be retrieved through the application. This vulnerability has been patched in v3.75.0. As a workaround, one may mitigate this vulnerability by disabling external file uploads via the `disableExternalFile` upload collection option, or by restricting `create` access on upload-enabled collections to trusted users only.