Why do I get the "Attribute contains invalid HTML" error when updating a knowledge article?

A security feature has been introduced in release 25A, which displays this error message preventing users from creating any HTML/CSS other than what the rich text area itself is capable of producing, blocking any content that could pose a security risk.

You can choose to disable this security feature, if you want to allow businesses to accept the security risk in favor of being able to create content beyond what is supported directly by the rich text area.

To disable this security feature:

1. Sign in as an administrator.
2. Go to Setup and Maintenance.
3. Select the Service offering and click Knowledge Management.
4. • For Fusion Service Knowledge Management with Redwood User Experience:
     1. Click the Manage Knowledge Content Types Redwood task.
     2. Edit the required content type.
     3. In the Scripting section, enable the Allow unrestricted JavaScript and HTML option.
     4. Click Save.
     5. Repeat these steps for all the required content types.
   • For Fusion Service Knowledge Management with Classic User Experience:
     1. Click the Manage Knowledge Content Types Classic task.
     2. Click the required content type name.
     3. In the Scripting section, select the Allow saving JavaScript and unsafe HTML option.
     4. Click Save.
     5. Repeat these steps for all the required content types.