CVE-2023-27592 — Cross-site Scripting in V2

Miniflux is a feed reader. Since v2.0.25, Miniflux will automatically proxy images served over HTTP to prevent mixed content errors. When an outbound request made by the Go HTTP client fails, the `html.ServerError` is returned unescaped without the expected Content Security Policy header added to valid responses. By creating an RSS feed item with the inline description containing an `` tag with a `srcset` attribute pointing to an invalid URL like `http:aalert(1)`, we can coerce the proxy handl…