The @vitest/browser Browser Mode exposes commands running on the Node.js side that interact with the local filesystem. Several commands accept file paths from the browser and perform operations without verifying the allowWrite permission or restricting paths to the project directory. This allows clients with access to the Browser Mode API to read arbitrary local files, write PNG screenshots or Playwright trace archives to arbitrary locations, and delete files, even when allowWrite is false. The vulnerability is most impactful when the API is network-exposed, as allowWrite defaults to false to block file access in such cases. The fix involves adding allowWrite checks and path confinement to all file-touching commands, rejecting absolute paths and directory traversal sequences.

An attacker able to reach the Browser Mode API can read arbitrary local files, exposing sensitive data. They can also create, overwrite, or delete files at arbitrary paths, though write operations are limited to generated PNG or trace archive files rather than attacker-controlled content. This leads to confidentiality breaches and potential integrity loss of files accessible by the Vitest process. The vulnerability is critical due to the ability to bypass intended file access restrictions and the potential for remote exploitation if the API is exposed beyond localhost.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. The planned fix adds allowWrite permission checks for write and delete operations and confines file paths to the project root, rejecting absolute paths and directory traversal. Until a patch is available, avoid exposing the Browser Mode API to untrusted networks or clients, and do not rely solely on allowWrite: false for security containment.