CVE-2025-20621 Webapp crash via object that can't be cast to String in Attachment Field

Mattermost versions 10.2.x = 10.2.0, 9.11.x = 9.11.5, 10.0.x = 10.0.3, 10.1.x = 10.1.3 fail to properly handle posts with attachments containing fields that cannot be cast to a String, which allows an attacker to cause the webapp to crash via creating and sending such a post to a channel...