The CommonInfo.Severity enumerated type defines the severity of the issues fixed in the update.
CRITICAL : Vulnerabilities that can be exploited by an unauthenticated attacker from the Internet or those that break the guest/host Operating System isolation. The exploitation results in the complete compromise of confidentiality, integrity, and availability of user data and/or processing resources without user interaction. Exploitation could be leveraged to propagate an Internet worm or execute arbitrary code between Virtual Machines and/or the Host Operating System.
IMPORTANT : Vulnerabilities that are not rated critical but whose exploitation results in the complete compromise of confidentiality and/or integrity of user data and/or processing resources through user assistance or by authenticated attackers. This rating also applies to those vulnerabilities which could lead to the complete compromise of availability when exploitation is by a remote unauthenticated attacker from the Internet or through a breach of virtual machine isolation.
MODERATE : Vulnerabilities where the ability to exploit is mitigated to a significant degree by configuration or difficulty of exploitation, but in certain deployment scenarios could still lead to the compromise of confidentiality, integrity, or availability of user data and/or processing resources.
LOW : All other issues that have a security impact. Vulnerabilities where exploitation is believed to be extremely difficult, or where successful exploitation would have minimal impact
Enumeration: CRITICAL, IMPORTANT, LOW, MODERATE,