Attack Chain

1. Attacker identifies a vulnerable Vitest instance with its UI server exposed to the network, running on a Windows system.
2. Attacker obtains the API token by sending a request to http://localhost:51204/__vitest__/.
3. Attacker crafts a malicious request to the /__vitest_attachment__ endpoint with a path traversal payload: http://localhost:51204/__vitest_attachment__?path=C:\\path\\to\\project\\?\\..\\..\\secret.txt&contentType=text/plain&token=$TOKEN.
4. The isFileServingAllowed check is bypassed due to the use of the \\?\\..\\ sequence.
5. The Vitest server reads the content of the specified file (secret.txt) outside the intended project directory.
6. The attacker receives the content of the file in the response.
7. Attacker leverages the API’s rerun feature and file write feature (saveTestFile) to write a malicious test file containing arbitrary code.
8. Attacker uses the rerun feature to execute the newly created test file, achieving arbitrary script execution.

Impact

Successful exploitation of this vulnerability allows an attacker to read arbitrary files on the affected system. If the attacker is able to read sensitive files containing credentials or configuration data, it could lead to further compromise of the system or network. The ability to execute arbitrary scripts allows for full system compromise, data exfiltration, or denial-of-service attacks. This vulnerability affects any Vitest instances with UI server exposed to network and running on Windows prior to version 4.1.0

Recommendation

• Upgrade Vitest to version 4.1.0 or later to patch CVE-2026-47429.
• Ensure that the allowWrite and allowExec configuration flags are disabled when the Vitest API server is bound to a non-localhost host as per the vendor mitigations.
• Monitor network traffic for suspicious requests to the /__vitest_attachment__ endpoint with path traversal sequences using the Sigma rule provided below.
• Monitor process creation for unexpected script execution originating from the Vitest process using the provided Sigma rule.