In Part 6 of the Active Directory Hardening Series, Jerry Devore emphasizes the importance of enforcing SMB signing as a critical security measure. He explains how SMB signing ensures message integrity and prevents NTLM relay attacks, detailing methods to mitigate risks, such as disabling broadcast name resolution and configuring network settings effectively.2. *
Active Directory Hardening Series: Part 6 – Enforcing SMB Signing
In the latest installment of the Active Directory Hardening series, Jerry Devore sheds light on the critical aspect of SMB signing. This security control is essential for maintaining the integrity of messages and preventing NTLM relay attacks.
What’s New in SMB Signing?
SMB signing is not just a technical detail; it’s a vital security measure. It ensures that messages exchanged between clients and servers remain intact and unaltered. As Devore notes, “Many of my Microsoft colleagues have already written some great content on SMB signing.” However, this topic deserves attention due to its importance in modern security protocols.
Understanding the Threat Landscape
Adversaries can exploit vulnerabilities in SMB signing through an Adversary-in-the-Middle (AiTM) attack. Surprisingly, this attacker does not need to be physically present. Instead, they can control an organization’s device remotely. Tools like Responder can listen for broadcast name resolution requests, allowing attackers to impersonate devices.
“An AiTM is most often not physically present but instead remotely controlling an organization’s device.”
Key Strategies for Mitigation
Organizations can significantly reduce risks by disabling broadcast name resolution methods like LLMNR and NBT-NS. Disabling LLMNR is straightforward and can be done through Group Policy Objects (GPO) or the registry. On the other hand, disabling NBT-NS can be more complex, especially in large networks.
To manage NBT-NS effectively, configuring the NetBT NodeType to P-node is recommended. This setting ensures that clients only use WINS for name resolution, eliminating the need for broadcasts.
Importance of Message Integrity
Message integrity in SMB parallels the concept of LDAP signing. During authentication, a symmetrical session key is established between the client and server. This key is crucial for generating a hash of each message, which is then signed and placed in the SMB packet header. If the signatures match, the recipient can trust that the message was not tampered with during transmission.
Final Thoughts
Enforcing SMB signing is a necessary step for organizations looking to bolster their security posture. As highlighted in this article, understanding the mechanisms behind SMB signing can empower IT professionals to implement effective security measures.
“A series on Active Directory hardening would not be complete without it.”
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