{"id":"GHSA-x7mm-9vvv-64w8","aliases":[],"url":"https://o3.security/vulnerability/GHSA-x7mm-9vvv-64w8","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 ``\n* `renderSSRHeadSuspenseChunk()` returned `window.${streamKey}.push(...)`\n\nNo escaping, quoting, or identifier validation was applied before these strings were embedded into HTML. A `streamKey` such as `__unhead__;globalThis.PWNED=1;//` broke out of the intended property access and injected arbitrary JavaScript into the page. The JSON escaping used for streamed head entries did not protect `streamKey` because `streamKey` was inserted as raw code rather than as serialized data.\n\n### Impact\n\n`streamKey` is a developer-chosen configuration value rather than a data field — the intended usage is a hardcoded identifier-shaped constant (default `__unhead__`). Exploitation therefore requires an application to explicitly route untrusted input into a configuration sink, which is not a documented or recommended pattern. We have no reports of any downstream project sourcing `streamKey` from request data.\n\nApplications using the default `streamKey`, or any hardcoded custom key, are **not affected**.\n\n### PoC\n\n```ts\nimport { createStreamableHead, renderSSRHeadShell } from 'unhead/stream/server'\n\nconst { head } = createStreamableHead({\n streamKey: '__unhead__;globalThis.PWNED=1;//',\n})\n\nconst html = renderSSRHeadShell(\n head,\n '',\n)\n\n// …\n```\n\n### Patch\n\nFixed on `main` in [`64b5ac0`](https://github.com/unjs/unhead/commit/64b5ac0aa30cc256ea6677ce3dc4f132f81b2ff6). The fix will ship in the next patch release of `unhead`.\n\n`streamKey` is now validated against a conservative ASCII JavaScript-identifier pattern (`/^[$_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.","published":"2026-04-10T22:09:39Z","modified":"2026-04-10T22:19:21.376374Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"unhead","fixedVersion":"3.0.1"}],"fix":{"url":"https://github.com/unjs/unhead/commit/64b5ac0aa30cc256ea6677ce3dc4f132f81b2ff6","label":"unjs/unhead@64b5ac0"},"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-04-10T22:19:21.376374Z"}}