According to the CVSS metric, privileges required is low (PR:L). Does the attacker need to be in an authenticated role on the Exchange Server? Yes, the attacker must be authenticated with LAN-access and have credentials for a valid Exchange user. According to the CVSS metrics, successful exploitation of this vulnerability could lead to major loss of confidentiality (C:H), integrity (I:H) and availability (A:H). What does that mean for this vulnerability? An attacker who successfully exploited this vulnerability could access a user's Net-NTLMv2 hash which could be used as a basis of an NTLM Relay attack against another service to authenticate as the user. What updates do I need to install to be protected from this vulnerability? Customers need to install the August 2023 Exchange security updates which are listed in the Security Updates table. Customers who have already August 2023 security updates are already protected from this vulnerability. Is there more information available? Yes, please see September 2023 release of new Exchange Server CVEs for more information.
Piotr Bazydlo (@chudypb) of Trend Micro Zero Day Initiative