How to Completely Disable ‘Web Serial API’ via Group Policy in Microsoft Edge

Modern web browsers support the Web Serial API, a powerful specification that allows websites to communicate directly with hardware peripherals connected to the local machine via serial ports (RS-232), USB-to-serial adapters, or built-in UART interfaces. This capability enables web-based configuration utilities for microcontrollers, 3D printers, or network switches. However, granting external web applications direct, low-level access to local serial buses introduces a massive operational security (OPSEC) and hardware exploitation liability in highly restricted enterprise, industrial control system (ICS), or zero-trust environments. A malicious or compromised website could silently enumerate connected hardware, inject unauthorized serial payloads, or bridge the air-gap between the browser sandbox and critical peripheral infrastructure.

This guide explains how to completely disable the ‘Web Serial API’ via Group Policy in Microsoft Edge, enforcing a strict cryptographic block that prevents all websites from requesting or initiating serial port communication.

Disable the Web Serial API via Group Policy

To enforce a strict configuration that explicitly strips the Chromium networking and hardware abstraction layer (HAL) of its ability to broker Web Serial API requests, overriding any user prompts or site permissions, we must deploy an administrative template.

1. Log into Windows with an Administrator account.
2. Press the Windows Key + R to open the Run dialogue box.
3. Type gpedit.msc and press Enter to launch the Local Group Policy Editor.
4. In the left-hand navigation pane, strictly follow this exact path:

   Computer Configuration > Administrative Templates > Microsoft Edge > Content settings

5. In the right-hand pane, locate the policy named Default Serial guard setting (internally known as DefaultSerialGuardSetting).
6. Double-click the policy to open its configuration window.
7. Select the radio button next to Enabled.
8. Under the Options section, locate the dropdown menu labeled “Default Serial guard setting”.
9. Explicitly select Block sites from connecting to serial ports (2). (By setting this integer value to 2, we instruct the Chromium V8 engine to proactively intercept and instantly reject any navigator.serial.requestPort() API call, ensuring the browser refuses to enumerate or bind to local serial hardware).
10. Click Apply, then click OK.

Verify the Configuration Lockdown

Group Policy changes modifying the Chromium hardware abstraction bridge require the browser to update its local policy state.

Close all active instances of Microsoft Edge. To force the policy update immediately across the OS, open Command Prompt as Administrator and run gpupdate /force. To verify the restriction is actively enforced, launch Microsoft Edge and navigate to edge://settings/content/serialPorts. You will immediately notice that the master toggle for “Ask when a site wants to connect to a serial port” is completely greyed out and locked in the “Off” position. A briefcase icon will confirm that the setting is managed by your organization. Furthermore, if you open the Developer Tools (F12) and attempt to invoke the Serial API via the console, the browser will throw an immediate NotAllowedError, confirming total hardware isolation.