{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.0.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "unhead"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0-beta.5"
            },
            {
              "fixed": "3.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-10T22:09:39Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "### Summary\n\n`createStreamableHead({ streamKey })` interpolated its `streamKey` argument directly into the streaming SSR bootstrap and suspense-chunk inline scripts without identifier validation or escaping. If an application forwards untrusted data into that configuration value, the rendered scripts become a script-injection sink.\n\n### Details\n\n`streamKey` was embedded into JavaScript source via dot notation in two public helpers:\n\n* `createBootstrapScript()` returned `\u003cscript\u003ewindow.${streamKey}={...}\u003c/script\u003e`\n* `renderSSRHeadSuspenseChunk()` returned `window.${streamKey}.push(...)`\n\nNo escaping, quoting, or identifier validation was applied before these strings were embedded into HTML. A `streamKey` such as `__unhead__;globalThis.PWNED=1;//` broke out of the intended property access and injected arbitrary JavaScript into the page. The JSON escaping used for streamed head entries did not protect `streamKey` because `streamKey` was inserted as raw code rather than as serialized data.\n\n### Impact\n\n`streamKey` is a developer-chosen configuration value rather than a data field \u2014 the intended usage is a hardcoded identifier-shaped constant (default `__unhead__`). Exploitation therefore requires an application to explicitly route untrusted input into a configuration sink, which is not a documented or recommended pattern. We have no reports of any downstream project sourcing `streamKey` from request data.\n\nApplications using the default `streamKey`, or any hardcoded custom key, are **not affected**.\n\n### PoC\n\n```ts\nimport { createStreamableHead, renderSSRHeadShell } from \u0027unhead/stream/server\u0027\n\nconst { head } = createStreamableHead({\n  streamKey: \u0027__unhead__;globalThis.PWNED=1;//\u0027,\n})\n\nconst html = renderSSRHeadShell(\n  head,\n  \u0027\u003c!doctype html\u003e\u003chtml\u003e\u003chead\u003e\u003c/head\u003e\u003cbody\u003e\u003c/body\u003e\u003c/html\u003e\u0027,\n)\n\n// \u003c!doctype html\u003e\u003chtml\u003e\u003chead\u003e\u003cscript\u003ewindow.__unhead__;globalThis.PWNED=1;//={_q:[],push(e){this._q.push(e)}}\u003c/script\u003e\u2026\n```\n\n### Patch\n\nFixed on `main` in [`64b5ac0`](https://github.com/unjs/unhead/commit/64b5ac0aa30cc256ea6677ce3dc4f132f81b2ff6). The fix will ship in the next patch release of `unhead`.\n\n`streamKey` is now validated against a conservative ASCII JavaScript-identifier pattern (`/^[$_a-z][$\\w]*$/i`) at every sink \u2014 `createStreamableHead`, `createBootstrapScript`, and the internal stream-key resolver. Invalid values throw immediately instead of being emitted into script output.\n\n### Workarounds\n\nDo not pass untrusted data into `createStreamableHead({ streamKey })` or `createBootstrapScript(key)`. If per-tenant keys are required, whitelist them against an identifier-safe pattern before constructing the head instance.\n\n### Credit\n\nThanks to @Jvr2022 for the report.",
  "id": "GHSA-x7mm-9vvv-64w8",
  "modified": "2026-04-10T22:09:39Z",
  "published": "2026-04-10T22:09:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/unjs/unhead/security/advisories/GHSA-x7mm-9vvv-64w8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/unjs/unhead/commit/64b5ac0aa30cc256ea6677ce3dc4f132f81b2ff6"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/unjs/unhead"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "unhead: Streaming SSR `streamKey` injected into inline script without identifier validation"
}