CVE-2021-22681

Rockwell Automation's Studio 5000 Logix Designer (versions 21 and later) and RSLogix 5000 (versions 16 through 20) use a shared key to verify that they are communicating with genuine Allen-Bradley Logix controllers, and an unauthenticated remote attacker can bypass this verification mechanism (CWE-522, insufficient protection of credentials). The attack requires only network access to the affected software or controllers - no credentials, no user interaction, and no special conditions (CVSS 3.1: 9.8). By bypassing the verification, an attacker can authenticate to CompactLogix, ControlLogix, DriveLogix, Compact GuardLogix, GuardLogix and SoftLogix controllers and interact with the PLCs, potentially tampering with industrial processes. Any deployment running the affected engineering software versions with the listed Logix controller families is in scope, which spans a very large share of Rockwell's installed base. CISA added this flaw to its Known Exploited Vulnerabilities catalog on 2026-03-05 (ransomware use unknown), and EPSS puts the 30-day exploitation probability at roughly 64%; no public proof-of-concept is known.

What to do: Apply mitigations per Rockwell's instructions - the vendor has advised disconnecting internet-facing connections, so remove internet exposure from affected controllers and engineering workstations and segment OT networks. Follow applicable CISA BOD 22-01 guidance, and inventory for Studio 5000 Logix Designer v21+ or RSLogix 5000 v16-20 used with the listed controllers; upgrade per vendor guidance or discontinue use if mitigations are unavailable.