Supported .Net Versions for Lync and Skype for Business Server

Finding information on this is difficult, I’ve built up this table after trawling through patch notes.
This section was last updated 25th of July 2019
A German version for Skype 2015 is over on MSxFaq’s blog here

Note that the major versions of .Net (ie, 3.x and 4.x) both run side by side on a server

.Net VersionMinimum Lync 2013 CU Minimum Skype4B 2015 CU Minimum Skype4B 2019 CU NoteMore Info
Security Update for .NET Framework (3156757) aka May 2017 .Net update
(Affects All Versions)
Known Issues Known Issues Known Issues Known Issues Patch introduces an issue with some clients connecting and web conferencing due to changes in encryption handling. Info and workaround here
.Net 3.5 Any Any Any RequiredRequired for installation. Lives alongside 4.X
.Net 3.5.1AnyAnyAnyYou may need to repair the .Net 4.x install if you install .Net 3.51 Example issue: https://greiginsydney.com/no-connectivity-with-the-lync-web-app/
4.0Out Of Support Out Of Support Out Of Support .Net 4.0 No longer in supportMore Info: https://devblogs.microsoft.com/dotnet/support-ending-for-the-net-framework-4-4-5-and-4-5-1/
4.4Out Of Support Out Of Support Out Of Support .Net 4.4 No longer in support More Info: https://devblogs.microsoft.com/dotnet/support-ending-for-the-net-framework-4-4-5-and-4-5-1/
4.5Out Of Support Out Of Support Out Of Support .Net 4.5 No longer in support More Info: https://devblogs.microsoft.com/dotnet/support-ending-for-the-net-framework-4-4-5-and-4-5-1/
4.5.2RTMRTMNot SupportedSkype4B 2013 CU6 and up require at least this version. Also required for Seafutil/OOS/OWASRecommended for new 2013 builds Download here
(why are you building a 2013 server?)
4.6.0RTMCU 5 – May 2017 Not SupportedHas security vulnerabilities, update to 4.6.22015: Conflicting info on this one, best idea is to update to CU5 and .net 4.7.2
4.6.1Not Supported Not Supported Not SupportedNot Supported on anything!
Upgrade to 4.6.2 if possible
Otherwise downgrade to 4.6.0

Warning: https://tomtalks.blog/2016/02/dont-install-net-framework-4-6-1-and-skype-for-business-server-2015-lync-server-2013-exchange-server/

Block install: https://support.microsoft.com/en-us/help/3133990/how-to-temporarily-block-the-installation-of-the-net-framework-4-6-1

Removal: http://www.expta.com/2016/02/how-to-uninstall-net-framework-461.html
4.6.2CU 8 HF1 – Nov 2016CU 4 HF1 – Feb 2017Not Supported Last supported .Net for Lync 20132019: Installer fails https://github.com/MicrosoftDocs/OfficeDocs-SkypeForBusiness/issues/2644
4.7.0 Not Supported CU 5 – May 2017 RTM 2015 Ref: https://docs.microsoft.com/en-us/skypeforbusiness/plan-your-deployment/requirements-for-your-environment/server-requirements%C2%A0
4.7.1
Not Supported
CU 5 – May 2017RTM
4.7.2 Not Supported CU 5 – May 2017 RTM Current recommended .Net for Skype4B 2015 and 2019Download here: https://download.microsoft.com/download/6/E/4/6E48E8AB-DC00-419E-9704-06DD46E5F81D/NDP472-KB4054530-x86-x64-AllOS-ENU.exe
4.8 Not Supported Not Supported Not Supported Yeah, no.

Server Updates

Updates for Skype for Business Server 2015 – Always points to the latest update.
Luca Vitali maintains a cache of older updates on his website. Skype4b 2015 and Lync 2013
A list of versions and their build numbers is over on Andrew Morpeth’s blog https://ucgeek.co/lync-updates/