The Hacker Newspublished May 1, 08:04 UTC (May 1, 2023)ingested Sep 10, 05:53 UTC@TheHackersNews

Microsoft Warns of Stealthy Outlook Vulnerability Exploited by Russian Hackers

criticalVulnerabilityimportance 60CVE-2023-23397

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Tagscve-2023-23397 vulnerability

Vulnerabilities mentionedAll →

CVE	Vulnerability	CVSS	EPSS	Flags	Affected	Exposure	Published
CVE-2023-23397	Zero-Click Elevation of Privilege in Microsoft Outlook (Forced NTLM Credential Leak) CVE-2023-23397 is an elevation of privilege vulnerability in Microsoft Outlook caused by improper input validation (CWE-20) combined with authentication bypass via spoofed authentication data on the channel (CWE-294), allowing an attacker to force Outlook to authenticate to an attacker-controlled SMB/WebDAV server. It is triggered when Outlook processes a crafted email or calendar object — for example a meeting or task reminder whose sound property points to an attacker-supplied UNC path — and requires no user interaction. That authentication exchange leaks the victim's NTLM credential hash, which the attacker can crack offline or relay to authenticate as the victim and access resources such as Exchange mailboxes, effectively escalating privileges. Affected software spans Microsoft 365 Apps, Microsoft Office (including the Long Term Servicing Channel), and Microsoft Outlook, which are deployed across enterprises, governments, and militaries worldwide. It is actively exploited in the wild — added to CISA's Known Exploited Vulnerabilities catalog on 2023-03-14 with a 97.4% EPSS — and Microsoft has warned of exploitation by Russia-aligned threat actors in campaigns against government and military mail servers, with patches shipped in Microsoft's March 2023 security updates. Do: Apply Microsoft's March 2023 security updates to Microsoft 365 Apps, Office/LTSC, and Outlook immediately, per CISA's required action. As interim mitigation, enable Extended Protection for Authentication or add accounts to the Protected Users group to block the NTLM credential leak, and audit calendar and task reminder sound properties for UNC paths (Microsoft published an audit/cleanup script for this) while watching for unexpected outbound SMB/WebDAV connections from hosts running Outlook.	9.8	97%	KEV	Microsoft 365 Apps Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges Microsoft Office Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges Microsoft Office Long Term Servicing Channel (LTSC) Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges +1 more	masson the order of hundreds of millions of users (Outlook ships with Microsoft Office/Microsoft 365, the dominant enterprise and government email suite)	Mar 14, 2023

CVE

Vulnerability

CVSS

EPSS

Flags

Affected

Exposure

Published

CVE-2023-23397

Zero-Click Elevation of Privilege in Microsoft Outlook (Forced NTLM Credential Leak)

CVE-2023-23397 is an elevation of privilege vulnerability in Microsoft Outlook caused by improper input validation (CWE-20) combined with authentication bypass via spoofed authentication data on the channel (CWE-294), allowing an attacker to force Outlook to authenticate to an attacker-controlled SMB/WebDAV server. It is triggered when Outlook processes a crafted email or calendar object — for example a meeting or task reminder whose sound property points to an attacker-supplied UNC path — and requires no user interaction. That authentication exchange leaks the victim's NTLM credential hash, which the attacker can crack offline or relay to authenticate as the victim and access resources such as Exchange mailboxes, effectively escalating privileges. Affected software spans Microsoft 365 Apps, Microsoft Office (including the Long Term Servicing Channel), and Microsoft Outlook, which are deployed across enterprises, governments, and militaries worldwide. It is actively exploited in the wild — added to CISA's Known Exploited Vulnerabilities catalog on 2023-03-14 with a 97.4% EPSS — and Microsoft has warned of exploitation by Russia-aligned threat actors in campaigns against government and military mail servers, with patches shipped in Microsoft's March 2023 security updates.

Do: Apply Microsoft's March 2023 security updates to Microsoft 365 Apps, Office/LTSC, and Outlook immediately, per CISA's required action. As interim mitigation, enable Extended Protection for Authentication or add accounts to the Protected Users group to block the NTLM credential leak, and audit calendar and task reminder sound properties for UNC paths (Microsoft published an audit/cleanup script for this) while watching for unexpected outbound SMB/WebDAV connections from hosts running Outlook.

9.8

97%

KEV

Microsoft 365 Apps Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges
Microsoft Office Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges
Microsoft Office Long Term Servicing Channel (LTSC) Affected builds as covered by Microsoft's March 2023 security updates; see Microsoft advisory for exact build ranges
+1 more

masson the order of hundreds of millions of users (Outlook ships with Microsoft Office/Microsoft 365, the dominant enterprise and government email suite)

Mar 14, 2023

Full article397 words · extracted from thehackernews.com · click to collapse

Ravie LakshmananMar 25, 2023Enterprise Security / Microsoft

Microsoft on Friday shared guidance to help customers discover indicators of compromise (IoCs) associated with a recently patched Outlook vulnerability.

Tracked as CVE-2023-23397 (CVSS score: 9.8), the critical flaw relates to a case of privilege escalation that could be exploited to steal NT LAN Manager (NTLM) hashes and stage a relay attack without requiring any user interaction.

"External attackers could send specially crafted emails that will cause a connection from the victim to an untrusted location of attackers' control," the company noted in an advisory released this month.

"This will leak the Net-NTLMv2 hash of the victim to the untrusted network which an attacker can then relay to another service and authenticate as the victim."

The vulnerability was resolved by Microsoft as part of its Patch Tuesday updates for March 2023, but not before Russia-based threat actors weaponized the flaw in attacks targeting government, transportation, energy, and military sectors in Europe.

Microsoft's incident response team said it found evidence of potential exploitation of the shortcoming as early as April 2022.

In one attack chain described by the tech giant, a successful Net-NTLMv2 Relay attack enabled the threat actor to gain unauthorized access to an Exchange Server and modify mailbox folder permissions for persistent access.

The compromised email account was then used to extend the adversary's access within the compromised environment by sending additional malicious messages to target other members of the same organization.

"While leveraging NTLMv2 hashes to gain unauthorized access to resources is not a new technique, the exploitation of CVE-2023-23397 is novel and stealthy," Microsoft said.

"Organizations should review SMBClient event logging, Process Creation events, and other available network telemetry to identify potential exploitation via CVE-2023-23397."

The disclosure comes as the U.S. Cybersecurity and Infrastructure Security Agency (CISA) released a new open source incident response tool that helps detect signs of malicious activity in Microsoft cloud environments.

Dubbed Untitled Goose Tool, the Python-based utility offers "novel authentication and data gathering methods" to analyze Microsoft Azure, Azure Active Directory, and Microsoft 365 environments, the agency said.

Earlier this year, Microsoft also urged customers to keep their on-premises Exchange servers updated as well as take steps to bolster their networks to mitigate potential threats.

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Text extracted automatically; images, tables and formatting may be missing. Original: https://thehackernews.com/2023/03/microsoft-warns-of-stealthy-outlook.html