A brand new zero-day vulnerability in NTLM found by researchers at 0patch permits attackers to steal NTLM credentials by having a consumer view a specifically crafted malicious file in Home windows Explorer — no want for the consumer to open the file. These password hashes can be utilized for authentication relay assaults or for dictionary assaults on the password, each for identification takeover.
NTLM refers to a collection of outdated authentication protocols from Microsoft that present authentication, integrity, and confidentiality to customers. Whereas NTLM was formally deprecated as of June, our analysis exhibits that 64% of Lively Listing consumer accounts often authenticate with NTLM — proof that NTLM remains to be extensively used regardless of its identified weaknesses.
The flaw is exploitable even in environments utilizing NTLM v2, making it a major danger to enterprises that haven’t but moved to Kerberos and are nonetheless counting on NTLM. Contemplating Microsoft could not patch this problem for some time, enterprise defenders ought to take steps to mitigate the vulnerability of their environments. This Tech Tip outlines how dynamic entry insurance policies, a number of hardening steps, and multifactor authentication (MFA) can assist restrict makes an attempt to take advantage of this vulnerability. Upgrading the protocol, the place attainable, might get rid of the problem utterly.
What Is the NTLM Vulnerability?
When a consumer views a malicious file in Home windows Explorer — whether or not by navigating to a shared folder, inserting a USB drive containing the malicious file, or simply viewing a file within the Downloads folder that was robotically downloaded from a malicious Net web page — an outbound NTLM connection is triggered. This causes Home windows to robotically ship NTLM hashes of the at the moment logged-in consumer to a distant attacker-controlled share.
These NTLM hashes can then be intercepted and used for authentication relay assaults and even dictionary assaults, granting attackers unauthorized entry to delicate techniques. Attackers may doubtlessly use the uncovered passwords to entry the group’s software-as-a-service (SaaS) surroundings because of the excessive charges of synced customers.
The difficulty impacts all Home windows variations from Home windows 7 and Server 2008 R2 as much as the newest Home windows 11 24H2 and Server 2022.
The basic drawback with NTLM lies in its outdated protocol design. NTLM transmits password hashes as a substitute of verifying plaintext passwords, making it weak to interception and exploitation. Even with NTLM v2, which makes use of stronger encryption, the hashes can nonetheless be captured and relayed by attackers. NTLM’s reliance on weak cryptographic practices and lack of safety in opposition to relay assaults are key weaknesses that make it extremely exploitable. Furthermore, NTLM authentication doesn’t assist trendy security measures, reminiscent of MFA, leaving techniques open to quite a lot of credential theft strategies, reminiscent of pass-the-hash and hash relaying.
What Defenders Must Do
To mitigate this vulnerability, Microsoft has up to date earlier steerage on methods to allow Prolonged Safety for Authentication (EPA) on LDAP, Lively Listing Certificates Companies (AD CS), and Trade Server. On Home windows Server 2022 and 2019, directors can manually allow EPA for AD CS and channel binding for LDAP. There are scripts supplied by Microsoft to activate EPA manually on Trade Server 2016. The place attainable, replace to the newest Home windows Server 2025 because it ships with EPA and channel binding enabled by default for each AD CS and LDAP.
Some organizations should still be depending on NTLM attributable to legacy techniques. These groups ought to contemplate extra authentication layers, reminiscent of dynamic risk-based insurance policies, for safeguarding current NTLM legacy techniques in opposition to exploitations.
Harden LDAP configurations. Configure LDAP to implement channel binding and monitor for legacy purchasers that will not assist these settings.
Test affect on SaaS. If you’re not sure whether or not there are purposes or purchasers in your surroundings that depend on NTLMv2, you need to use Group Coverage to allow the Community Safety: Limit NTLM: Audit incoming NTLM site visitors coverage setting. This is not going to block NTLMv2 site visitors however will log all makes an attempt to authenticate utilizing NTLMv2 within the Operations Log. By analyzing these logs, you’ll be able to determine which shopper purposes, servers, or providers nonetheless depend on NTLMv2, so you can also make focused changes or updates.
Utilizing Group Coverage to restrict or disable NTLM authentication by way of the Community Safety: Limit NTLM setting will scale back the danger of fallback situations the place NTLM is unintentionally used.
Monitor SMB site visitors. Enabling SMB signing and encryption can assist stop attackers from impersonating respectable servers and triggering NTLM authentication. Blocking outbound SMB site visitors to untrusted networks may also scale back the danger of NTLM credential leakage to rogue servers. Implement community monitoring and alerting for uncommon SMB site visitors patterns, significantly outbound requests to unknown or untrusted IP addresses.
Depart NTLM behind. NTLM has been deprecated. Directors ought to audit NTLM utilization to determine which techniques nonetheless depend on NTLM. Organizations ought to prioritize transitioning these techniques away from NTLM to extra trendy authentication protocols, reminiscent of Kerberos. As soon as a extra trendy protocol is in place, implement MFA so as to add an extra layer of safety.
Taking these steps will assist organizations handle the elemental flaws in NTLM and enhance their safety posture.
