An attacker could send crafted SMTP packets to cause a denial-of-service condition where the controller enters a major non-recoverable faulted state (MNRF) in CompactLogix 5370 L1, L2, and L3 Controllers, Compact GuardLogix 5370 controllers, and Armor Compact GuardLogix 5370 Controllers Versions 20 to 30.014 and earlier.