CVE-2026-47429

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

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 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.

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

The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.

CVE-2026-47429 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.1.0, 3.2.6); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-47429? CVE-2026-47429 is a critical-severity missing authorization vulnerability in vitest (npm), affecting versions >= 4.0.0, < 4.1.0. It is fixed in 4.1.0, 3.2.6. The application does not perform an authorization check before performing a sensitive operation.
2. How severe is CVE-2026-47429? CVE-2026-47429 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of vitest are affected by CVE-2026-47429? vitest (npm) versions >= 4.0.0, < 4.1.0 is affected.
4. Is there a fix for CVE-2026-47429? Yes. CVE-2026-47429 is fixed in 4.1.0, 3.2.6. Upgrade to this version or later.
5. Is CVE-2026-47429 exploitable, and should I be worried? Whether CVE-2026-47429 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47429 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47429?
   • Upgrade vitest to 4.1.0 or later
   • Upgrade vitest to 3.2.6 or later