CVE-2026-54299: Astro Host Header SSRF Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2pvr-wf23-7pc7",
  "modified" : "2026-08-12T20:37:21Z",
  "published" : "2026-06-16T14:38:06Z",
  "aliases" : [ "CVE-2026-54299" ],
  "summary" : "Astro: Host header SSRF in prerendered error page fetch",
  "details" : "## Summary\n\nAstro SSR apps with prerendered error pages (`/404` or `/500` using `export const prerender = true`) fetch those pages over HTTP at runtime when an error occurs. The URL for this fetch is derived from `request.url`, which in turn gets its origin from the incoming `Host` header. When the `Host` header is not validated against `allowedDomains`, an attacker can point the fetch at an arbitrary host and read the response.\n\n## Who is affected\n\nThis affects SSR deployments that:\n\n1. Have a prerendered 404 or 500 page\n2. Use `createRequestFromNodeRequest` from `astro/app/node` with `app.render()` **without** overriding `prerenderedErrorPageFetch` — this includes custom servers built on the public API and third-party adapters\n\n**Not affected:**\n- `@astrojs/node` >= 9.5.4 (reads error pages from disk)\n- `@astrojs/cloudflare` (uses the ASSETS binding)\n- The dev server (renders error pages in-process)\n\n## How it works\n\n`createRequestFromNodeRequest` builds `request.url` from the raw `Host` / `:authority` header. The `allowedDomains` option is accepted but only gates `X-Forwarded-For` — it does not constrain the URL origin. (The public `createRequest` does fall back to `localhost` for unvalidated hosts; this internal builder did not.)\n\nWhen `app.render()` encounters a 404 or 500 with a prerendered error route, `default-handler.ts` constructs the error page URL using the origin from `request.url` and fetches it via `prerenderedErrorPageFetch`, which defaults to global `fetch`. The response body is served to the client.\n\nAn attacker sends a request with `Host: attacker-host:port`, triggers an error (e.g., requesting a nonexistent path for a 404), and receives the response from the attacker-controlled host reflected back.\n\n## Remediation\n\nThe error page fetch origin is now validated against `allowedDomains` before use. When the host is validated, the original origin is preserved. Otherwise, it falls back to `localhost`. The fetch is also wrapped in a try/catch so that connection failures degrade gracefully to a plain error response.\n\n## Credit\n\n5ud0 / Tarmo Technologies",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "astro"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.4.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/security/advisories/GHSA-2pvr-wf23-7pc7"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-54299"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/withastro/astro"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-16T14:38:06Z",
    "nvd_published_at" : "2026-06-22T19:17:21Z"
  }
}