Impact
An unauthenticated user can retrieve Prometheus metrics from a publicly reachable Miniflux instance where the METRICSCOLLECTOR configuration option is enabled and METRICSALLOWEDNETWORKS is set to 127.0.0.1/8 (the default).
Patches
PR #1745 fixes the problem. Available in Miniflux >= 2.0.43.
Workarounds
Set METRICSCOLLECTOR to false (default) or run Miniflux behind a trusted reverse-proxy.
References
- https://miniflux.app/docs/configuration.html#metrics-collector - https://miniflux.app/docs/configuration.html#metrics-allowed-networks
Impact
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 <img> tag with a srcset attribute pointing to an invalid URL like http:a<script>alert(1)</script>, we can coerce the proxy handler into an error condition where the invalid URL is returned unescaped and in full.
This results in JavaScript execution on the Miniflux instance as soon as the user is convinced (e.g. by a message in the alt text) to open the broken image.
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 gain administrative access to the Miniflux instance if it is reachable and the victim is an administrator.
Patches
PR #1746 fixes the problem. Available in Miniflux >= 2.0.43.
Workarounds
- Disable image proxy (default value is http-only).
References
- https://miniflux.app/docs/configuration.html#proxy-images
Summary
Due to a weak Content Security Policy on the /proxy/ route, an attacker can bypass the CSP of the media proxy and execute cross-site scripting when opening external images in a new tab/window.
Impact
A malicious feed added to Miniflux can execute arbitrary JavaScript in the user's browser when opening external resources, such as proxified images, in a new tab or window.
Mitigation
The CSP for the media proxy has been changed from default-src 'self' to default-src 'none'; form-action 'none'; sandbox;.
Upgrade to Miniflux >= 2.2.7
Credit RyotaK (GMO Flatt Security Inc.) with takumi-san.ai