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Internet Explorer Processes

This policy controls consistent MIME handling in Windows 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_HANDLING\(Reserved)
  • HKLM\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_HANDLING\explorer.exe
  • HKLM\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_HANDLING\iexplore.exe
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_HANDLING\(Reserved)
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_HANDLING\explorer.exe
  • HKCU\Software\Policies\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MIME_HANDLING\iexplore.exe

This policy controls consistent MIME handling in Windows Explorer and Internet Explorer processes. Internet Explorer compares several indicators for the type of a file received from a web server: the file name extension, the HTTP Content-Type and Content-Disposition headers, and the type detected by examining the file signature.

When the policy is enabled, these indicators must be consistent. For example, if Internet Explorer detects executable content while the server identifies the file as text/plain, it does not rely solely on the apparently less dangerous server-supplied type. Files with conflicting type information are renamed and moved to the Internet Explorer cache.

When the policy is disabled, Internet Explorer does not require consistent MIME information for files received by these processes. The current Microsoft policy reference documents the not-configured state as retaining the same consistency requirement as the enabled state.

Notes

Security

Consistent MIME handling makes it more difficult to deliver executable or otherwise risky content under an inaccurate, apparently harmless file extension or MIME declaration. Disabling the policy removes this additional consistency check for the covered processes. This increases the risk that incorrectly declared content will be handled according to misleading type information.

This feature is neither antimalware scanning nor a general download block. It checks whether type indicators agree; malicious files with internally consistent type information are not necessarily detected or blocked.

Possible side effects

If a web server or application supplies conflicting MIME types, file extensions, or Content-Disposition information, the resulting file name, cache location, or subsequent handling can change. Legacy or incorrectly configured web applications may therefore exhibit different download or open behavior.

Notes

The ADMX template uses a REG_SZ value for each of the three named values: 1 enables the feature and 0 disables it. explorer.exe and iexplore.exe scope the behavior to the corresponding processes. (Reserved) is also part of the Microsoft template definition; the public policy description does not document a separate runtime function for this reserved entry.

The setting is available in both Computer Configuration and User Configuration. The HKLM path has machine-wide scope, while the HKCU path has user scope. Other applications that host the Internet Explorer WebBrowser control are not covered by the process-specific values listed here.

This policy is distinct from the separate FEATURE_MIME_SNIFFING control. FEATURE_MIME_HANDLING checks consistency among multiple type indicators, whereas FEATURE_MIME_SNIFFING controls file-type detection from a file signature.

Microsoft documentation

Microsoft Learn: InternetExplorer Policy CSP – ConsistentMimeHandlingInternetExplorerProcesses

Microsoft Learn: INTERNETFEATURELIST enumeration – FEATURE_MIME_HANDLING

See also