CVE-2026-25545 PoC — Astro has Full-Read SSRF in error rendering via Host: header injection

Title:Astro has Full-Read SSRF in error rendering via Host: header injection (CVE-2026-25545)
Description: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.

Astro before 5.17.3 and @astrojs/node before 9.5.4 are vulnerable to full-read SSRF due to improper Host header validation in error page rendering, allowing attackers to redirect requests and access internal resources.

 id: CVE-2026-25545

info:
  name: Astro SSR - Server-Side Request Forgery
  author: ritikchaddha
  s

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