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The HTTP fallback for SIP connection in Lync must be disabled.


Overview

Finding ID Version Rule ID IA Controls Severity
V-223345 O365-LY-000002 SV-223345r508019_rule Medium
Description
Prevents from HTTP being used for SIP connection in case TLS or TCP fail.
STIG Date
Microsoft Office 365 ProPlus Security Technical Implementation Guide 2022-06-17

Details

Check Text ( C-25018r442254_chk )
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".

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

HKLM\Software\Policies\Microsoft\office\16.0\lync

If the value disablehttpconnect is REG_DWORD = 1, this is not a finding.
Fix Text (F-25006r442255_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".