Reports suggest the vulnerability is currently being leveraged by Russian state-sponsored APT groups. These credentials can then be used in NTLM relay attacks against the victim. If the reminder triggers while Outlook is open, a connection to the SMB share is initiated containing the user’s hashed password in an NTLM negotiation message. This property is modified to reference an external universal naming convention (UNC) path to a Server Message Block (SMB) share on an attacker-controlled server. In an attack scenario, threat actors would deliver a crafted email containing the PidLidReminderFileParameter extended Messaging Application Programming Interface (MAPI) property. Microsoft has released an impact assessment script that may be used to identify if organizations were targeted by threat actors attempting to exploit CVE-2023-23397ĬVE-2023-23397 is highly concerning as exploitation does not require previous access or any user interaction.Block outbound SMB (TCP port 445) from the network by using a perimeter firewall, a local firewall, and via VPN settings.Add users to the Protected Users group in Active Directory.If patching is not immediately possible, Microsoft has provided temporary alternative mitigations.
After performing a business impact review, apply the relevant security patches from Microsoft.eSentire security teams are tracking this vulnerability for additional details and detection opportunities.Related malicious IP addresses have been added to the eSentire blocklist.Threat hunts related to the exploitation of CVE-2023-23397 are ongoing.eSentire Managed Vulnerability Service (MVS) has plugins in place to identify CVE-2023-23397.eSentire Threat Intelligence assesses it is almost certain threat actors will adopt the technique for use in attacks in the immediate future. As exploitation has been observed in limited cases, immediate patching of CVE-2023-23397 is critical. Exploitation of this vulnerability would allow a threat actor to access an impacted user’s Net-NTLMv2 hash, enabling future NTLM Relay attacks to authenticate to other services as the user.ĬVE-2023-23397 is relatively simple to exploit, and its success has already been proven in real world attacks as such, widespread exploitation is expected in the immediate future. The vulnerability is tracked as CVE-2023-23397 (CVSS: 9.8) - Microsoft Outlook Elevation of Privilege vulnerability. On March 14th, as part of Microsoft’s monthly Patch Tuesday release, the company disclosed a critical, actively exploited vulnerability impacting Microsoft Office and Outlook.
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