Miniflux Media Proxy SSRF via /proxy endpoint allows access to internal network resources

Miniflux 2 is an open source feed reader. Prior to version 2.2.16, Miniflux's media proxy endpoint (GET /proxy/{encodedDigest}/{encodedURL}) can be abused to perform Server-Side Request Forgery (SSRF). An authenticated user can cause Miniflux to generate a signed proxy URL for attacker-chosen media URLs embedded in feed entry content, including internal addresses (e.g., localhost, private RFC1918 ranges, or link-local metadata endpoints). Requesting the resulting /proxy/... URL makes Miniflux fetch and return the internal response. Version 2.2.16 fixes the issue.