TinyMCE not initializing on CMS 12 after upgrading to .NET 10

Farhin

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Hi,

We've upgraded our Optimizely CMS 12 solution to.NET 10 and noticed that TinyMCE no longer initializes for XhtmlString properties. Instead of the editor toolbar, content editors see the raw HTML markup in a plain text box.

Environment

CMS UI: 12.34.4
CMS Core / Framework: 12.24.0
EPiServer.CMS.TinyMce: 5.0.3
Target Framework: .NET 10

What we've checked

Application builds and runs successfully.
TinyMCE is configured using the standard CMS 12 setup (AddEpiserverSupport())
CSP is in report-only mode.
TinyMCE 13.x is not an option due to CMS 12 dependency conflicts.

Observations

EPiServer.CMS.TinyMce 5.0.3 only ships a net 6.0 assembly.
The issue appears to be related to TinyMCE client resources or editor initialization not loading correctly under .NET 10.

Questions

Has anyone successfully run CMS 12 + TinyMCE 5.0.3 on .NET 10?
Have you encountered TinyMCE failing to initialize after a framework upgrade?
Any specific browser console errors, module loading issues, or resource registration checks you'd recommend investigating?

Thanks in advance for any insights!

#343041

Edited, Jul 16, 2026 21:01

Farhin

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Episerver Support Response on the issue:

This is a known issue (our reference CMS-52767) and not a problem with your setup or with the net6.0 target of the TinyMce assembly. To answer your questions:

Yes, CMS 12 officially supports .NET 10 as of CMS 12.34.4 — see our announcement: https://world.optimizely.com/blogs/bien-nguyen/dates/2026/5/optimizely-cms-12-now-fully-supports-.net-10. The net6.0 assemblies roll forward and are supported.

2 and 3. There is a known issue matching your exact symptom. A permanent fix is verified and will ship in EPiServer.CMS.TinyMce 5.0.4 (not yet published at the time of writing)
Please watch https://world.optimizely.com/support/Bug-list/bug/CMS-52767, https://nuget.optimizely.com/packages/EPiServer.CMS.TinyMce/ and the 2026 CMS 12 release notes https://support.optimizely.com/hc/en-us/articles/33309043090189-2026-Optimizely-CMS-12-release-notes

#343048

Jul 17, 2026 14:04