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 22nd of October 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 Required Required for installation. Lives alongside 4.X
.Net 3.5.1 Any Any Any You may need to repair the .Net 4.x install if you install .Net 3.51 after 4.xExample issue: https://greiginsydney.com/no-connectivity-with-the-lync-web-app/
.Net 4.0Out Of Support Out Of Support Out Of Support .Net 4.0 No longer in support

More Info: https://devblogs.microsoft.com/dotnet/support-ending-for-the-net-framework-4-4-5-and-4-5-1/
.Net 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/
.Net 4.5Out Of Support Out Of Support Out Of Support .Net 4.5 No longer in supportMore Info: https://devblogs.microsoft.com/dotnet/support-ending-for-the-net-framework-4-4-5-and-4-5-1/
.Net 4.5.2RTM RTM Not Supported Skype4B 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?)
.Net 4.6.0RTM CU 5 – May 2017 Not Supported Has security vulnerabilities
update to 4.6.2
2015: Conflicting info on this one, best idea is to update to CU5 and .net 4.7.2
.Net 4.6.1Not Supported Not Supported Not Supported Not 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
.Net 4.6.2 CU 4 HF1 – Feb 2017 CU 4 HF1 – Feb 2017 Not Supported Last supported .Net for Lync 2013 2019: Installer fails https://github.com/MicrosoftDocs/OfficeDocs-SkypeForBusiness/issues/2644
.Net 4.7.0Not Supported CU 5 – May 2017 RTM2015 Ref: https://docs.microsoft.com/en-us/skypeforbusiness/plan-your-deployment/requirements-for-your-environment/server-requirements%C2%A0
.Net 4.7.1Not Supported CU 5 – May 2017 RTM
.Net 4.7.2Not Supported CU 5 – May 2017 RTM Current recommended .Net for Skype4B 2015 Download here: https://download.microsoft.com/download/6/E/4/6E48E8AB-DC00-419E-9704-06DD46E5F81D/NDP472-KB4054530-x86-x64-AllOS-ENU.exe
.Net 4.8 Not Supported Not Supported RTM Current recommended .Net for Skype4B 2019 Download here: https://support.microsoft.com/en-au/help/4503548/microsoft-net-framework-4-8-offline-installer-for-windows

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/