9.8

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3.1

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CVE-2026-47429

CVE-2026-47429: 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. https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/ui/node/index.ts#L77 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.

https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/vitest/src/api/setup.ts#L103-L105
https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/vitest/src/api/setup.ts#L119-L121
https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/browser/src/node/commands/fs.ts#L10-L11
https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/browser/src/node/plugin.ts#L194-L196
https://github.com/vitest-dev/vitest/blob/eb1abf08573032a532015b999ad3501c5e89e3bb/packages/browser/src/node/rpc.ts#L115-L121

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 . This means exposing the API / Vitest UI is equivalent to giving script execution access. On the browser mode side, there're / / . So exposing the browser mode is equivalent to giving file read / write access.

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CVE-2026-47429

CVE-2026-47429:

9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
vitest	npm	>= 4.0.0, < 4.1.0	4.1.0
vitest	npm	< 3.2.6	3.2.6

Technical Details

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Root Cause Analysis

The root cause of the vulnerability is a path traversal flaw in how file paths from user input were validated. Specifically, the isFileServingAllowed function was used incorrectly, allowing it to be bypassed on Windows systems using special path sequences like \\?\\..\\. This flaw was present in multiple locations across the Vitest codebase, affecting the UI, browser testing mode, and the developer API server.

This vulnerability manifested in several ways:

Arbitrary File Read: The most direct exploitation was through the /__vitest_attachment__ endpoint, where an attacker could read any file on the filesystem that the Vitest process had access to.
Arbitrary File Write/Delete: Functions like writeFile, removeFile, and saveSnapshotFile were also vulnerable, allowing an attacker to create, modify, or delete files in arbitrary locations.
Arbitrary Code Execution: The most critical impact was the ability to achieve remote code execution. An attacker could use a file-write primitive like saveTestFile to create a malicious test file and then use an execution primitive like rerun to have Vitest execute it.

The patch addresses this vulnerability with a two-pronged approach. First, it replaces the incorrect usage of isFileServingAllowed with a more secure implementation that properly cleans and validates file paths, fixing the underlying path traversal bug. Second, it introduces new security controls, api.allowWrite and api.allowExec, which are disabled by default when the Vitest server is exposed to the network. This acts as a defense-in-depth measure, preventing file write and execution operations even if a similar vulnerability were to be discovered in the future, effectively putting the UI in a read-only mode in such configurations.

Vulnerable functions

attachment_middleware

packages/ui/node/index.ts

The primary vulnerability highlighted in the advisory is a path traversal flaw in the middleware handling `/__vitest_attachment__` requests. This handler used the `isFileServingAllowed` function incorrectly, failing to sanitize the user-provided `path` parameter. This allowed an attacker to craft a path that bypassed the security check (e.g., `C:\\path\\to\\project\\?\\..\\..\\secret.txt`) and read arbitrary files from the server's filesystem on Windows. The function name is inferred as it's an anonymous middleware handler.

readFile

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

The `readFile` function is exposed via browser commands and was vulnerable to path traversal. The `assertFileAccess` function it relied on used the flawed `isFileServingAllowed` check, which could be bypassed on Windows using special path characters (`\\?\\..\\`). This allowed an attacker to read arbitrary files from the filesystem outside of the project root. The patch corrects this by cleaning the path using `slash()` and using the more secure `isFileLoadingAllowed` function within `assertFileAccess`.

writeFile

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

Similar to `readFile`, the `writeFile` function was vulnerable to path traversal. An attacker could write files to arbitrary locations on the filesystem by exploiting the bypass in `isFileServingAllowed`. The patch mitigates this by fixing the path validation in `assertFileAccess` and introducing a new `assertWrite` check, which is gated by the `api.allowWrite` configuration option, providing a defense-in-depth security control.

removeFile

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

The `removeFile` function was vulnerable to the same path traversal flaw as `readFile` and `writeFile`. This allowed an attacker to delete arbitrary files from the filesystem. The patch applies the same fixes: correcting the path validation and adding the `assertWrite` check.

saveSnapshotFile

packages/browser/src/node/rpc.ts

Exposed via RPC, `saveSnapshotFile` used the vulnerable `checkFileAccess` function, making it susceptible to path traversal. An attacker could write snapshot files to arbitrary locations. The patch introduces a `canWrite` check, which respects the new `api.allowWrite` setting, preventing file writes when the server is exposed to the network.

removeSnapshotFile

packages/browser/src/node/rpc.ts

Similar to `saveSnapshotFile`, the `removeSnapshotFile` RPC method was vulnerable to path traversal, allowing arbitrary file deletion. The patch adds the `canWrite` check to prevent this when file writing is disabled for security reasons.

saveTestFile

packages/vitest/src/api/setup.ts

The `saveTestFile` function, exposed through the WebSocket API, allowed writing to test files. While intended for use in the UI, it could be abused to write arbitrary content to files. When combined with a rerun command, this leads to code execution. The patch adds a check for the `api.allowWrite` configuration to restrict this capability.

rerun

packages/vitest/src/api/setup.ts

The `rerun` function, part of the WebSocket API, triggers test execution. The vulnerability description highlights that if an attacker can write a malicious test file (e.g., via `saveTestFile`), they can use `rerun` to execute it, leading to arbitrary code execution. The patch introduces an `api.allowExec` check to gate this functionality.

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WAF Protection Rules

WAF Rule

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Reasoning

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CVE-2026-47429: When Vitest UI server is listening, arbitrary file can be read and executed

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CVE-2026-47429: When Vitest UI server is listening, arbitrary file can be read and executed

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CVE-2026-47429: When Vitest UI server is listening, arbitrary file can be read and executed

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9.8

CVE-2026-47429: When Vitest UI server is listening, arbitrary file can be read and executed

Summary

Impact

Details

PoC

Mitigations

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Vulnerable functions

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