Attack Chain

1. Initial Access: The attacker gains network access to the Vitest Browser Mode API, typically by exploiting a misconfigured test.api.host or a publicly exposed development server.
2. API Interaction: The attacker sends a crafted request to a vulnerable Browser Mode command (e.g., upload, takeScreenshot, deleteTracing).
3. Path Traversal/Absolute Path Injection: The attacker includes an absolute path or path traversal sequences (e.g., ../) in the file path parameter of the command.
4. Permission Bypass: The vulnerable command processes the client-supplied path without checking the allowWrite permission gate.
5. Arbitrary File Operation: Depending on the command used, the Vitest process performs an operation on the specified arbitrary file path.

• upload or annotateTraces: Reads the contents of an arbitrary local file and discloses them to the attacker.
• takeScreenshot, screenshotMatcher, stopChunkTrace: Creates or overwrites files (e.g., PNGs, .zip archives) at arbitrary locations.
• deleteTracing: Deletes arbitrary files by path.

6. Impact: The attacker achieves arbitrary file read/write/delete capabilities, leading to data exfiltration, system manipulation, or denial of service.

Impact

The vulnerability allows an attacker with network access to the Vitest Browser Mode API to perform arbitrary file system operations on the host running the Vitest process. This can lead to severe consequences, including the exfiltration of sensitive data from any accessible file (e.g., configuration files, private keys, source code) via commands like upload or annotateTraces. Attackers can also compromise system integrity by creating, overwriting, or deleting critical files using commands such as takeScreenshot or deleteTracing. While writes are limited to specific file types (PNGs, zip archives), the ability to delete arbitrary files or overwrite existing ones with attacker-controlled, albeit type-restricted, content could lead to a denial of service or further system compromise. The severity is particularly high if the Vitest environment has elevated privileges or contains sensitive data.

Recommendation

• Patch Vulnerable Vitest Installations: Immediately update @vitest/browser to a fixed version: >= 3.2.7, >= 4.1.10, or >= 5.0.0-beta.6.
• Network Segmentation: Ensure that the Vitest Browser Mode API (test.api.host) is not exposed to untrusted networks or the internet. Restrict network access to only trusted development environments.
• Principle of Least Privilege: Run Vitest processes with the minimum necessary file system permissions to limit the blast radius of any potential exploitation.
• Monitor for Anomalous File Activity: Implement logging and monitoring for unusual file read, write, or delete operations originating from Vitest processes that exceed expected behavior.