Insufficient checks whether ReCAPTCHA was enabled made it possible to bypass the checks on the login page. This did not affect other pages where ReCAPTCHA is utilized.
Incorrect validation of allowed event types in a calendar web service made it possible for some users to create events with types/audiences they did not have permission to publish to.
The Chat activity in Moodle 4.3.3 allows students to insert a potentially unwanted HTML A element or IMG element, or HTML content that leads to a performance degradation. NOTE: the vendor's Using_Chat page says "If you know some HTML code, you can use it in your text to do things like insert images, play sounds or create different coloured and sized text." This page also says "Chat is due to be removed from standard Moodle."
Separate Groups mode restrictions were not honored in the H5P attempts report, which would display users from other groups. By default this only provided additional access to non-editing teachers.