Net-NTLMv2 hash leak in Microsoft Outlook

Published: 2023-03-14 | Updated: 2023-12-19
Risk Critical
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2023-23397
Exploitation vector Network
Public exploit This vulnerability is being exploited in the wild.
Vulnerable software
Microsoft Outlook
Client/Desktop applications / Office applications

Microsoft Office
Client/Desktop applications / Office applications

Vendor Microsoft

Security Bulletin

This security bulletin contains one critical risk vulnerability.

1) Information disclosure

EUVDB-ID: #VU73511

Risk: Critical

CVSSv3.1: 7.2 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:H/RL:O/RC:C]

CVE-ID: CVE-2023-23397

CWE-ID: CWE-200 - Information exposure

Exploit availability: Yes


The vulnerability allows a remote attacker to compromise the affected system.

The vulnerability exists due to the application leaks the Net-NTLMv2 hash. A remote attacker can send a specially crafted email to the victim and obtain the Net-NTLMv2 hash of the Windows account. The victim does not need to open the email, as the vulnerability is triggered automatically when it is retrieved and processed by the email server, e.g. before the email is viewed in the preview pane.

The obtained NTLMv2 hash can be used in the NTLM Relay attack against another service to authenticate as the user.

Note, the vulnerability is being actively exploited in the wild.


Install updates from vendor's website.

Vulnerable software versions

Microsoft Outlook: 2013 - 2021

Microsoft Office: 365 - 2021

External links

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to trick the victim to visit a specially crafted website or open a file.

Is there known malware, which exploits this vulnerability?

Yes. This vulnerability is being exploited in the wild.