Summary
unhead: Streaming SSR streamKey injected into inline script without identifier validation
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<script>window.${streamKey}={...}</script>renderSSRHeadSuspenseChunk()returnedwindow.${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.
PoC
import { createStreamableHead, renderSSRHeadShell } from 'unhead/stream/server'
const { head } = createStreamableHead({
streamKey: '__unhead__;globalThis.PWNED=1;//',
})
const html = renderSSRHeadShell(
head,
'<!doctype html><html><head></head><body></body></html>',
)
// <!doctype html><html><head><script>window.__unhead__;globalThis.PWNED=1;//={_q:[],push(e){this._q.push(e)}}</script>…
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.
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.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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.
Frequently Asked Questions
- What is GHSA-X7MM-9VVV-64W8? GHSA-X7MM-9VVV-64W8 is a low-severity cross-site scripting (XSS) vulnerability in unhead (npm), affecting versions >= 3.0.0-beta.5, <= 3.0.0. It is fixed in 3.0.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which versions of unhead are affected by GHSA-X7MM-9VVV-64W8? unhead (npm) versions >= 3.0.0-beta.5, <= 3.0.0 is affected.
- Is there a fix for GHSA-X7MM-9VVV-64W8? Yes. GHSA-X7MM-9VVV-64W8 is fixed in 3.0.1. Upgrade to this version or later.
- Is GHSA-X7MM-9VVV-64W8 exploitable, and should I be worried? Whether GHSA-X7MM-9VVV-64W8 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-X7MM-9VVV-64W8 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-X7MM-9VVV-64W8? Upgrade
unheadto 3.0.1 or later.