Stored XSS in Miniflux when opening a broken image due to unescaped ServerError in proxy handler

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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 `<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. A patch is available in version 2.0.43. As a workaround sisable image proxy; default value is `http-only`.

Source published

17 Mar 2023 19:04:00 UTC

Source modified

25 Feb 2025 14:53:55 UTC

Saved here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 4.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N

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 `<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. A patch is available in version 2.0.43. As a workaround sisable image proxy; default value is `http-only`.

Source published

Mar 17, 2023, 7:04:00 PM (timezone not stated)

Source modified

Feb 25, 2025, 2:53:55 PM (timezone not stated)

Saved here

14 Nov 2026 03:00:44 UTC

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EUVD CVSS 3.1 · 4.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N

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 `<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. A patch is available in version 2.0.43. As a workaround sisable image proxy; default value is `http-only`.

Source published

17 Mar 2023 20:15:13 UTC

Source modified

17 Jun 2026 05:45:32 UTC

Saved here

24 Oct 2026 21:17:34 UTC

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CVSS 3.1 · [email protected] · Secondary · 4.8 CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N

CVSS 3.1 · [email protected] · Primary · 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

### Impact Since [v2.0.25](https://github.com/miniflux/v2/releases/tag/2.0.25), Miniflux will automatically [proxy](https://miniflux.app/docs/configuration.html#proxy-images) 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](https://github.com/miniflux/v2/blob/b2fd84e0d376a3af6329b9bb2e772ce38a25c31c/ui/proxy.go#L76) unescaped without the expected Content Security Policy [header](https://github.com/miniflux/v2/blob/b2fd84e0d376a3af6329b9bb2e772ce38a25c31c/ui/proxy.go#L90) 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

Source published

2 Apr 2025 17:25:15 UTC

Source modified

10 Sep 2026 03:50:57 UTC

Saved here

24 Oct 2026 13:19:41 UTC

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GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:H/A:N

Publisher rating · MODERATE