Sitecore RTE broken after security patch - h is not a constructor

Sitecore - Telerik RTE broken

Recently we installed the Sitecore Security Bulletin SC2025-004 on a project that is deployed on Azure as a PAAS solution. The project includes SXA, so we also installed the Cumulative hotfix for SXA 10.2.0 and Sitecore XP 10.2 as was mentioned in the security bulletin (for sites running on 10.2 - there are different versions for the other Sitecore releases).

At first everything seemed fine, but then we noticed the Telerik Rich Text Editor (RTE) wasn't working anymore. Or at least, the display of it was completely wrong:

We are still not sure if this was actually related to the patch install, but it was only happening on both environments where those got installed and it was still fine on the production environment that did not have it. Also worth mentioned we could not reproduce it locally, although we also installed the whole patch there.

Sitecore StackExchange

I started searching for a solution and while doing that bumped into someone on Sitecore StackExchange who seems to have faced the same issue - although it is until now not yet clear if  he also experienced this after installing a patch or not. But the issue was the same, the PAAS environment as well and so is the error. Anyways, after finding a fix I also posted it there so I hope he reads it someday and can fix his issue as well. You can check the post on https://sitecore.stackexchange.com/a/39965/237. 

The error - h is not a constructor

Our main starting point to solving the issue was the error above that we got in the browser. I found my way to a Telerik knowledge-base article that mentions the error: TypeError: h is not a constructor at Sys.Component.create.

As you probably know, the Rich Text Editor in Sitecore XM/XP is from Telerik, and although the error message stack trace was not completely the same as mine, the solution was worth a shot as it was close enough.

Solution

The solution is adding a setting in the appSettings part of the web.config. Note that many solutions (including ours) rip this part from the actual web.config to place it in a separate file. The section should already contain some keys related to the Telerik editor. Add this: 

<configuration>

  <appSettings>

<add key="ValidationSettings:UnobtrusiveValidationMode" value="None" />

Once this was added, the Telerik editor was working fine again. So far, we haven't found any other issues with it so we can assume this has fixed it.

As at least one other person encountered this I thought there might be more so it was worth sharing. If you have it as well, I hope this fixes it for you as well.