CVE-2026-47428 is a critical-severity (CVSS 9.6) Cross-site Scripting (XSS) vulnerability in @vitest/browser. O3 Security confirms whether CVE-2026-47428 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Vitest browser mode serves unsanitized otelCarrier query parameter as inline script
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47428.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-47428 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@vitest/browsernpmDescription
Vitest is a testing framework powered by Vite. From 4.0.17 until 4.1.6 and 5.0.0-beta.3, Vitest Browser Mode served /vitest_test/ with the otelCarrier query parameter inserted directly into an inline module script, allowing a crafted browser-runner URL to execute arbitrary JavaScript in the Vitest server origin and recover VITEST_API_TOKEN for authenticated API calls. This issue is fixed in versions 4.1.6 and 5.0.0-beta.3.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @vitest/browser | ≥ 4.0.17&&< 4.1.6 | 4.1.6 |
| 📦npm | @vitest/browser | ≥ 5.0.0-beta.0&&< 5.0.0-beta.3 | 5.0.0-beta.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @vitest/browser. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @vitest/browser to 4.1.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47428 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-47428 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-47428. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat has assessed this flaw against its shipping products. The vulnerability requires @vitest/browser (Vitest's opt-in Browser Mode) to be installed and actively enabled; it does not affect the core `vitest` test runner used without Browser Mode. None of Red Hat's shipping products install or execute…
Frequently Asked Questions
Is CVE-2026-47428 in your dependencies?
O3 detects CVE-2026-47428 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.