CVE-2023-27592: 
NixOS vulnerability analysis and mitigation

CVE-2023-27592 affects Miniflux, a feed reader application, from version 2.0.25 to 2.0.42. The vulnerability was discovered in March 2023 and involves a cross-site scripting (XSS) issue in the image proxy functionality (GitHub Advisory, NVD).

The vulnerability occurs when Miniflux automatically proxies 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. The vulnerability has a CVSS v3.1 base score of 4.8 (Medium) with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N (GitHub Advisory).

An attacker can execute arbitrary JavaScript in the context of a victim Miniflux user when they open a broken image in a crafted RSS feed. This can be used to perform actions on the Miniflux instance as that user and potentially gain administrative access if the victim is an administrator (GitHub Advisory).

The exploit can be triggered by creating an RSS feed item with an inline description containing an <img> tag with a srcset attribute pointing to an invalid URL like http:aalert(1). This coerces the proxy handler into an error condition where the invalid URL is returned unescaped and in full, resulting in JavaScript execution when the user is convinced to open the broken image (GitHub Advisory).

The vulnerability was patched in Miniflux version 2.0.43. As a workaround, users can disable the image proxy functionality (the default value is 'http-only') (GitHub Advisory, Miniflux Docs).