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Internet Explorer Processes

This ADMX-backed Group Policy setting controls the MIME Sniffing Safety Feature for the specified Explorer and Internet Explorer processes.

since 0.9.8.11

Purpose

Show registry keys (6)
  • HKLM\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\(Reserved)
  • HKLM\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\explorer.exe
  • HKLM\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\iexplore.exe
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\(Reserved)
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\explorer.exe
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_SNIFFING\iexplore.exe

This ADMX-backed Group Policy setting controls the MIME Sniffing Safety Feature for the specified Explorer and Internet Explorer processes. MIME sniffing examines a file’s binary signature to determine its actual content type, which Internet Explorer can then use when deciding how to render or otherwise handle the file.

When the policy is enabled, MIME sniffing cannot promote a file from an apparently safer type to a more dangerous file type. This is particularly relevant when a file’s actual structure does not match the MIME type supplied by the web server. When the policy is disabled, the affected processes may perform such a promotion. According to Microsoft, the unconfigured state also prevents promotion to a more dangerous type.

The values under HKLM represent the device scope, while those under HKCU represent the user scope. The explorer.exe and iexplore.exe entries limit the feature control to the named processes.

Notes

Security

Preventing dangerous MIME promotions reduces the risk that deliberately mislabeled content will be handled as an active or executable file type. For example, a resource presented as plain text might contain executable or otherwise active content.

Disabling the policy removes this protective layer. Detection of a more dangerous type does not by itself guarantee code execution: subsequent handling still depends on factors such as the security zone, the detected type, its registered handler, and other Internet Explorer security controls.

Possible side effects

Incorrectly configured web applications or servers may send an inaccurate MIME type and rely on Internet Explorer to correct it after inspecting the content. If that correction would promote the resource to a more dangerous type, enabling the safety feature can cause the content to render differently, fail to open as intended, or be rejected.

Notes

This setting is not a system-wide MIME policy for every Windows application or browser. It is a process-specific Internet Explorer feature control for the listed executable files.

Internet Explorer security-zone policies can additionally determine whether MIME sniffing is permitted for a particular URL. This setting is also related to, but does not replace, the Consistent MIME Handling policy. Consistent MIME Handling compares information such as the file-name extension, HTTP headers, and the type detected from the content.

Microsoft does not document a separate functional behavior for the template value named (Reserved); the documented behavior applies to the policy as a whole.

Microsoft documentation

Microsoft Learn: InternetExplorer Policy CSP – MimeSniffingSafetyFeatureInternetExplorerProcesses

Microsoft Learn: INTERNETFEATURELIST enumeration – FEATURE_MIME_SNIFFING

See also