Connect with us

Hi, what are you looking for?

SecurityWeekSecurityWeek

Vulnerabilities

NTLM Relay Attack Abuses Windows RPC Protocol Vulnerability

A newly identified NTLM (New Technology LAN Manager) relay attack abuses a remote procedure call (RPC) vulnerability to enable elevation of privilege, researchers from cybersecurity firm SentinelOne reveal.

A newly identified NTLM (New Technology LAN Manager) relay attack abuses a remote procedure call (RPC) vulnerability to enable elevation of privilege, researchers from cybersecurity firm SentinelOne reveal.

The security hole, which apparently affects all versions of Windows, enables an attacker to escalate privileges from User to Domain Admin, all without requiring interaction from the user (NTLM relay attacks typically do require user intervention).

The researchers used a DCOM client that was instructed to connect to a RPC server, operation that involved two NTLM authentications, one without the “Sign flag” being set, and also leveraged the fact that the DCOM activation service can be abused to trigger RPC authentication.

The idea behind the attack, SentinelLabs explains, was that a shell in Session 0, even as a low privileged user, combined with triggering some CLSIDs, could allow the attacker to obtain “an NTLM authentication from the user who is interactively connected.”

The attack works as follows: the attacker has a shell in Session 0 on the target machine, even with a low privileges account; a user with high privileges (such as Domain Admin) logs in interactively; the attacker triggers the DCOM activation service to impersonate the high-privileged user; the attacker implements a man-in-the-middle to receive an authenticated call; the binding of the RPC under the attacker’s control takes place; the victim machine makes an authenticated call; authentication is relayed to a privileged resource such as LDAP, SMB, HTTP or other; the authentication is forwarded for privilege escalation.

SentinelLabs also released proof-of-concept code to demonstrate how the exploit works, and reveals that, although Microsoft has acknowledged the vulnerability, a patch won’t be released.

The researchers, however, did publish a series of mitigations that should help prevent attacks that would trigger an authenticated RPC/DCOM call and then relay the NTLM authentication.

“This is different from other known techniques such as CVE-2020-1113 and CVE-2021-1678, where relaying happens between a generic ‘client’ protocol vs. an RPC server. In this case, we had an RPC client whose authentication was relayed to other ‘server’ protocols and without ‘victim’ interaction. Therefore, we hope that MS reconsider their decision not to fix this serious vulnerability,” SentinelLabs concludes.

Advertisement. Scroll to continue reading.

Related: CrowdStrike Discloses Details of Recently Patched Windows NTLM Vulnerability

Related: Microsoft Patches Critical Vulnerabilities in NTLM

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

Click to comment

Trending

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

Discover strategies for vendor selection, integration to minimize redundancies, and maximizing ROI from your cybersecurity investments. Gain actionable insights to ensure your stack is ready for tomorrow’s challenges.

Register

Dive into critical topics such as incident response, threat intelligence, and attack surface management. Learn how to align cyber resilience plans with business objectives to reduce potential impacts and secure your organization in an ever-evolving threat landscape.

Register

People on the Move

The City of Phoenix has promoted Mitch Kohlbecker to the role of Chief Information Security Officer.

Gigamon has promoted Tony Jarjoura to CFO and Ram Bhide has been hired as Senior VP of engineering.

Cloud security firm Mitiga has appointed Charlie Thomas as Chief Executive Officer.

More People On The Move

Expert Insights

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest cybersecurity news, threats, and expert insights. Unsubscribe at any time.