MIME sniffing must be disallowed (Restricted Sites zone).

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-15524	DTBI470	SV-45278r1_rule	ECSC-1	Medium

Description
This policy setting allows you to manage MIME sniffing for file promotion from one type to another based on a MIME sniff. A MIME sniff is the recognition by Internet Explorer of the file type based on a bit signature. If you enable this policy setting, the MIME Sniffing Safety Feature will not apply in this zone. The security zone will run without the added layer of security provided by this feature. If you disable this policy setting, the actions that may be harmful cannot run; this Internet Explorer security feature will be turned on in this zone, as dictated by the feature control setting for the process. If you do not configure this policy setting, the MIME Sniffing Safety Feature will not apply in this zone.

Description

This policy setting allows you to manage MIME sniffing for file promotion from one type to another based on a MIME sniff. A MIME sniff is the recognition by Internet Explorer of the file type based on a bit signature. If you enable this policy setting, the MIME Sniffing Safety Feature will not apply in this zone. The security zone will run without the added layer of security provided by this feature. If you disable this policy setting, the actions that may be harmful cannot run; this Internet Explorer security feature will be turned on in this zone, as dictated by the feature control setting for the process. If you do not configure this policy setting, the MIME Sniffing Safety Feature will not apply in this zone.

STIG	Date
Microsoft Internet Explorer 10 Security Technical Implementation Guide	2014-07-03

Details

Check Text ( C-42625r1_chk )
The policy value for Computer Configuration -> Administrative Templates -> Windows Components -> Internet Explorer -> Internet Control Panel -> Security Page -> Restricted Sites Zone -> "Enable MIME Sniffing" must be "Enabled", and "Disable" selected from the drop-down box. Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\4 Criteria: If the value 2100 is REG_DWORD = 3, this is not a finding.

Check Text ( C-42625r1_chk )

The policy value for Computer Configuration -> Administrative Templates -> Windows Components -> Internet Explorer -> Internet Control Panel -> Security Page -> Restricted Sites Zone -> "Enable MIME Sniffing" must be "Enabled", and "Disable" selected from the drop-down box.

Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\4

Criteria: If the value 2100 is REG_DWORD = 3, this is not a finding.

Fix Text (F-38674r1_fix)
Set the policy value for Computer Configuration -> Administrative Templates -> Windows Components -> Internet Explorer -> Internet Control Panel -> Security Page -> Restricted Sites Zone -> "Enable MIME Sniffing" to "Enabled", and select "Disable" from the drop-down box.