GHSA-x7mm-9vvv-64w8: unhead Streaming SSR `streamKey` Injected Into Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-x7mm-9vvv-64w8",
  "modified" : "2026-04-10T22:09:39Z",
  "published" : "2026-04-10T22:09:39Z",
  "aliases" : [ ],
  "summary" : "unhead: Streaming SSR `streamKey` injected into inline script without identifier validation",
  "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 `<script>window.${streamKey}={...}</script>`\n* `renderSSRHeadSuspenseChunk()` returned `window.${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 — 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 'unhead/stream/server'\n\nconst { head } = createStreamableHead({\n  streamKey: '__unhead__;globalThis.PWNED=1;//',\n})\n\nconst html = renderSSRHeadShell(\n  head,\n  '<!doctype html><html><head></head><body></body></html>',\n)\n\n// <!doctype html><html><head><script>window.__unhead__;globalThis.PWNED=1;//={_q:[],push(e){this._q.push(e)}}</script>…\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 — `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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "unhead"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0-beta.5"
      }, {
        "fixed" : "3.0.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.0.0"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-10T22:09:39Z",
    "nvd_published_at" : null
  }
}