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EUVD-2026-270964

fkie_cve-2026-25545

Astro is a web framework. Prior to version 9.5.4, Server-Side Rendered pages that return an error with a prerendered custom error page (eg. `404.astro` or `500.astro`) are vulnerable to SSRF. If the `Host:` header is changed to an attacker's server, it will be fetched on `/500.html` and they can redirect this to any internal URL to read the response body through the first request. An attacker who can access the application without `Host:` header validation (eg. through finding the origin IP behind a proxy, or just by default) can fetch their own server to redirect to any internal IP. With this they can fetch cloud metadata IPs and interact with services in the internal network or localhost. For this to be vulnerable, a common feature needs to be used, with direct access to the server (no proxies). Version 9.5.4 fixes the issue.

GHSA-qq67-mvv5-fw3g — Astro has Full-Read SSRF in error rendering via Host: header injection

Affected: npm: @astrojs/node

### Summary

Server-Side Rendered pages that return an error with a prerendered custom error page (eg. `404.astro` or `500.astro`) are vulnerable to SSRF. If the `Host:` header is changed to an attacker's server, it will be fetched on `/500.html` and they can redirect this to any internal URL to read the response body through the first request.

### Details

The following line of code fetches `statusURL` and returns the response back to the client:

https://github.com/withastro/astro/blob/bf0b4bfc7439ddc565f61a62037880e4e701eb05/packages/astro/src/core/app/base.ts#L534

`statusURL` comes from `this.baseWithoutTrailingSlash`, which [is built from the `Host:` header](https://github.com/withastro/astro/blob/e5e3208ee5041ad9cccd479c29a34bf6183a6505/packages/astro/src/core/app/node.ts#L81). `prerenderedErrorPageFetch()` is just `fetch()`, and **follows redirects**. This makes it possible for an attacker to set the `Host:` header to their server (eg. `Host: attacker.tld`), and if the server still receives the request without normalization, Astro will now fetch `http://attacker.tld/500.html`.

The attacker can then redirect this request to http://localhost:8000/ssrf.txt, for example, to fetch any locally listening service. The response code is not checked, because as the comment in the code explains, this fetch may give a 200 OK. The body and headers are returned back to the attacker.

Looking at the vulnerable code, the way to reach this is if the `renderError()` function is calle…