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

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-223301	SRG-APP-000179	O365-CO-000019	SV-223301r961050_rule	2025-03-05	3

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.

ℹ️ Check
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.

ℹ️ Check

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
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.