GHSA-x7mm-9vvv-64w8 unhead: Streaming SSR `streamKey` injected into inline script without identifier validation

• npm unhead: >= 3.0.0-beta.5, < 3.0.1 → fixed in 3.0.1

Summary `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. Details `streamKey` was embedded into JavaScript source via dot notation in two public helpers: • `createBootstrapScript()` returned `window.${streamKey}={...}` • `renderSSRHeadSuspenseChunk()` returned `window.${streamKey}.push(...)` No 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. Impact `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. Applications using the default `streamKey`, or any hardcoded custom key, are not affected. PoC ```ts import { createStreamableHead, renderSSRHeadShell } from 'unhead/stream/server' const { head } = createStreamableHead({ streamKey: '__unhead__;globalThis.PWNED=1;//', }) const html = renderSSRHeadShell( head, '', ) // window.__unhead__;globalThis.PWNED=1;//={_q:[],push(e){this._q.push(e)}}… ``` Patch Fixed on `main` in `64b5ac0`. The fix will ship in the next patch release of `unhead`. `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. Workarounds Do 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. Credit Thanks to @Jvr2022 for the report.