CVE-2026-41322: Astro Cache Poisoning Due To Incorrect Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c57f-mm3j-27q9",
  "modified" : "2026-04-27T16:42:14Z",
  "published" : "2026-04-23T14:36:03Z",
  "aliases" : [ "CVE-2026-41322" ],
  "summary" : "Astro: Cache Poisoning due to incorrect error handling when if-match header is malformed ",
  "details" : "### Summary\nRequesting a static JS/CSS resource from the `_astro` path with an incorrect or malformed `if-match` header returns a `500` error with a one-year cache lifetime instead of `412` in some cases. As a result, all subsequent requests to that file — regardless of the `if-match` header — will be served a 5xx error instead of the file until the cache expires.\n\nSending an incorrect or malformed `if-match` header should always return a `412` error without any cache headers, which is not the current behavior.\n\n### Affected Versions\n- `astro@5.14.1`\n- `@astrojs/node@9.4.4`\n\n### Proof of Concept\n\nRun the following command:\n\n```\ncurl -s -o /dev/null -D - <host location>/_astro/_slug_.UTbyeVfw.css -H \"if-match: xxx\"\n```\n\nIf a 5xx error is not returned, inspect the resources via the browser's web inspector and select another CSS/JS file to request until a 5xx error is returned. The behavior generally defaults to a 5xx response. Note that all static files are immutable, so the cache must be purged or disabled to reproduce reliably.\n\nA response similar to the following is expected from CloudFront:\n\n```\nHTTP/2 500 \ncontent-type: text/html\ncontent-length: 166541\ndate: Thu, 09 Apr 2026 12:53:08 GMT\nlast-modified: Wed, 21 Jan 2026 13:40:08 GMT\netag: \"a68349e96c2faf8861c330aeb548441a\"\nx-amz-server-side-encryption: AES256\naccept-ranges: bytes\nserver: AmazonS3\nx-cache: Error from cloudfront\nvia: 1.1 3591be88662e5675a9dc1cc4e0a9c392.cloudfront.net (CloudFront)\nx-amz-cf-pop: ZRH55-P2\nx-amz-cf-id: Rg--RIYCKcA55GZqZXdvu-VTvpxBFFVzV4LBIcKq5pB_hktcrhYbKg==\n```\n\nThe above is not the real server output but the AWS error response triggered when the pods return a 5xx. Below is the output of the same `curl` command issued directly against a pod in Kubernetes:\n\n```\n❯ curl -s -o /dev/null -D - -H \"Host: tagesanzeiger.ch\" 127.0.0.1:3333/_astro/InstallPrompt.astro_astro_type_script_index_0_lang.C0M4llHG.js -H \"if-match: xxx\"\n\nHTTP/1.1 500 Internal Server Error\nCache-Control: public, max-age=31536000, immutable\nAccept-Ranges: bytes\nLast-Modified: Tue, 07 Apr 2026 07:08:03 GMT\nETag: W/\"560-19d66c50c38\"\nContent-Type: text/javascript; charset=utf-8\nDate: Tue, 07 Apr 2026 08:23:54 GMT\nConnection: keep-alive\nKeep-Alive: timeout=5\nTransfer-Encoding: chunked\n```\n\nThis demonstrates that the pod itself returns a `5xx` error instead of `412`. In addition, the response includes a `Cache-Control: public, max-age=31536000, immutable` header.\n\nBecause the testing setup configures `if-match` as part of the cache key, the exploit no longer affects the production application. Prior to that change, the CDN Point of Presence would become cache-poisoned, and any client visiting the affected pages without cached files through the same PoP would receive broken pages. This was reproduced by creating test URLs and visiting them in a browser only after triggering the exploit. The exploited resources returned `5xx` errors instead of the original CSS/JS content, breaking the application.\n\n### Details\nThe findings were analyzed with an LLM, which identified the following file as the likely source: [serve-static.ts](https://github.com/withastro/astro/blob/main/packages/integrations/node/src/serve-static.ts)\n\n```js\n// Lines 129-153\n\nlet forwardError = false;\n\nstream.on('error', (err) => {\n    if (forwardError) {\n        console.error(err.toString());\n        res.writeHead(500);\n        res.end('Internal server error');\n        return;\n    }\n    // File not found, forward to the SSR handler\n    ssr();\n});\nstream.on('headers', (_res: ServerResponse) => {\n    // assets in dist/_astro are hashed and should get the immutable header\n    if (normalizedPathname.startsWith(`/${app.manifest.assetsDir}/`)) {\n        // This is the \"far future\" cache header, used for static files whose name includes their digest hash.\n        // 1 year (31,536,000 seconds) is convention.\n        // Taken from https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control#immutable\n        _res.setHeader('Cache-Control', 'public, max-age=31536000, immutable');\n    }\n});\nstream.on('file', () => {\n    forwardError = true;\n});\nstream.pipe(res);\n```\n\nLLM analysis:\n\n> `send` handles conditional request headers such as `If-Match` internally. When a file is found but the precondition fails (ETag mismatch), `send`:\n>\n> 1. Emits `file` (the file exists) → `forwardError = true`\n> 2. Emits `headers` → `Cache-Control: public, max-age=31536000, immutable` is set on `res`\n> 3. Emits `error` with a `PreconditionFailedError` (status 412)\n>\n> However, the error handler does not inspect the error's status code:\n>\n> ```js\n> stream.on('error', (err) => {\n>     if (forwardError) {\n>         console.error(err.toString());\n>         res.writeHead(500);   // ← always 500, regardless of the actual error\n>         res.end('Internal server error');\n>         return;\n>     }\n>     ssr();\n> });\n> ```\n>\n> Because `Cache-Control` was already set during the `headers` event, the response is sent as:\n>\n> ```\n> HTTP/1.1 500 Internal Server Error\n> Cache-Control: public, max-age=31536000, immutable\n> ```\n\n\n### Impact\n**Cache Poisoning** — An attacker can force edge servers to cache an error page instead of the actual content, rendering one or more assets unavailable to legitimate users until the cache expires.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@astrojs/node"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "10.0.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/withastro/astro/security/advisories/GHSA-c57f-mm3j-27q9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41322"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/withastro/astro"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-525" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-23T14:36:03Z",
    "nvd_published_at" : "2026-04-24T18:16:28Z"
  }
}