Disable MIME Sniffing for Downloads in Regedit

MIME format sniffing allows Windows and Internet Explorer components to determine a file’s type by inspecting its binary content rather than relying on its file extension. While designed for convenience, disabling this feature prevents ambiguous files from automatically executing as programs. This guide explains how to disable MIME format sniffing for downloads using the Windows Registry Editor.

Method 1: Disable MIME Sniffing via Internet Zone Policies

This method changes the security zone settings to prevent files from opening based on their content.

  1. Press Win + R, type regedit, and press Enter to open the Registry Editor.

  2. Navigate to the following key for the current user:

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3

    (Note: Zone 3 represents the Internet Zone. To apply this to the Local Intranet or Trusted Sites, modify zones 1 or 2 respectively).

  3. In the right pane, locate the DWORD (32-bit) value named 2100 (this controls “Open files based on content, not file extension”).

    • If 2100 does not exist, right-click an empty area, select New > DWORD (32-bit) Value, and name it 2100.

  4. Double-click 2100, set the Value data to 3 (Disable), and click OK.

    • 0 = Enabled
    • 3 = Disabled

  5. (Optional) To apply this globally for all users on the machine, repeat the steps under:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3

Method 2: Disable MIME Sniffing via FeatureControl

This method completely disables the MIME sniffing feature engine across applications and executables.

  1. In the Registry Editor, navigate to:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl

  2. Look for a subkey named FEATURE_MIME_SNIFFING. If it does not exist:

    • Right-click FeatureControl, select New > Key, and name it FEATURE_MIME_SNIFFING.

  3. Select FEATURE_MIME_SNIFFING, right-click in the right pane, and choose New > DWORD (32-bit) Value.

  4. Name the value * (to apply to all processes) or iexplore.exe (for Internet Explorer/WebOC components).

  5. Double-click the newly created value, set its Value data to 0, and click OK.

  6. If running a 64-bit version of Windows, repeat this process in the 32-bit compatibility path:

    HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING

Applying the Changes

  1. Close the Registry Editor.
  2. Restart any active browsers or restart the computer to ensure the new registry policies take effect.