The MIME Sniffing safety feature must be enabled in all Office programs.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-223301	O365-CO-000019	SV-223301r508019_rule		Medium

Description
Encryption is only as good as the encryption modules utilized. Unapproved cryptographic module algorithms cannot be verified and cannot be relied upon to provide confidentiality or integrity, and DoD data may be compromised due to weak algorithms. The use of TLS provides confidentiality of data in transit between the application server and client. FIPS 140-2 approved TLS versions include TLS V1.0 or greater. TLS must be enabled and non-FIPS-approved SSL versions must be disabled. NIST SP 800-52 specifies the preferred configurations for government systems.

Description

Encryption is only as good as the encryption modules utilized. Unapproved cryptographic module algorithms cannot be verified and cannot be relied upon to provide confidentiality or integrity, and DoD data may be compromised due to weak algorithms. The use of TLS provides confidentiality of data in transit between the application server and client. FIPS 140-2 approved TLS versions include TLS V1.0 or greater. TLS must be enabled and non-FIPS-approved SSL versions must be disabled. NIST SP 800-52 specifies the preferred configurations for government systems.

STIG	Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide	2021-12-17

Details

Check Text ( C-24974r442122_chk )
Verify the policy value for Computer Configuration >> Administrative Templates >> Microsoft Office 2016 (Machine) >> Security Settings >> IE Security >> Mime Sniffing Safety Feature is set to "Enabled" and the check box is selected for every installed Office program. Use the Windows Registry Editor to navigate to the following key: HKLM\software\microsoft\internet explorer\main\featurecontrol\feature_mime_sniffing If the value for all installed Office Programs is REG_DWORD = 1, this is not a finding.

Check Text ( C-24974r442122_chk )

Verify the policy value for Computer Configuration >> Administrative Templates >> Microsoft Office 2016 (Machine) >> Security Settings >> IE Security >> Mime Sniffing Safety Feature is set to "Enabled" and the check box is selected for every installed Office program.

Use the Windows Registry Editor to navigate to the following key:

HKLM\software\microsoft\internet explorer\main\featurecontrol\feature_mime_sniffing

If the value for all installed Office Programs is REG_DWORD = 1, this is not a finding.

Fix Text (F-24962r442123_fix)
Set the policy value for Computer Configuration >> Administrative Templates >> Microsoft Office 2016 (Machine) >> Security Settings >> IE Security >> Mime Sniffing Safety Feature to "Enabled" for all installed Office programs.