CVE 2021-22681 https://www.rockwellautomation.com/en-us/trust-center/security-advisories/advisory.PN1550.html and send a specially crafted CIP message to the device. If exploited, a threat actor could help prevent access to the legitimate user and end connections to connected devices including the workstation. To recover the controllers, a download is required which ends any process that the controller is running.
A specific malformed fragmented packet type (fragmented packets may be generated automatically by devices that send large amounts of data) can cause a major nonrecoverable fault (MNRF) Rockwell Automation's ControlLogix 5580, Guard Logix 5580, CompactLogix 5380, and 1756-EN4TR. If exploited, the affected product will become unavailable and require a manual restart to recover it. Additionally, an MNRF could result in a loss of view and/or control of connected devices.