In the event a secure Session Initiation Protocol (SIP) connection fails, the connection must be restricted from resorting to the unencrypted HTTP.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-70905	SRG-APP-000219	DTOO422	SV-85529r1_rule	2016-11-02	1

Description
Prevents from HTTP being used for SIP connection in case TLS or TCP fail.

ℹ️ Check
Verify the policy value for Computer Configuration -> Administrative Templates -> Skype for Business 2016 -> Microsoft Lync Feature Policies "Disable HTTP fallback for SIP connection" is set to "Enabled". Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\office\16.0\lync Criteria: If the value disablehttpconnect is REG_DWORD = 1, this is not a finding.

ℹ️ Check

Verify the policy value for Computer Configuration -> Administrative Templates -> Skype for Business 2016 -> Microsoft Lync Feature Policies "Disable HTTP fallback for SIP connection" is set to "Enabled". Procedure: Use the Windows Registry Editor to navigate to the following key: HKLM\Software\Policies\Microsoft\office\16.0\lync Criteria: If the value disablehttpconnect is REG_DWORD = 1, this is not a finding.

✔️ Fix
Set the policy value for Computer Configuration -> Administrative Templates -> Skype for Business 2016 -> Microsoft Lync Feature Policies "Disable HTTP fallback for SIP connection" to "Enabled".