Session Initiation Protocol (SIP) security mode must be configured.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-70903	SRG-APP-000219	DTOO421	SV-85527r1_rule	2016-11-02	1

Description
When Lync connects to the server, it supports various authentication mechanisms. This policy allows the user to specify whether Digest and Basic authentication are supported. Disabled (default): NTLM/Kerberos/TLS-DSK/Digest/Basic Enabled: Authentication mechanisms: NTLM/Kerberos/TLS-DSK Gal Download: Requires HTTPS if user is not logged in as an internal user.

ℹ️ Check
Verify the policy value for Computer Configuration -> Administrative Templates -> Skype for Business 2016 -> Microsoft Lync Feature Policies "Configure SIP security mode" 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 enablesiphighsecuritymode 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 "Configure SIP security mode" 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 enablesiphighsecuritymode 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 "Configure SIP security mode" to "Enabled".