A brand new zero-day vulnerability in NTLM discovered by researchers at 0patch permits attackers to steal NTLM credentials by having a person view a specifically crafted malicious file in Home windows Explorer — no want for the person 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NTLM refers to a set of outdated authentication protocols from Microsoft that present authentication, integrity, and confidentiality to customers. Whereas NTLM was officially deprecated as of June, our analysis exhibits that 64% of Active Directory user accounts frequently authenticate with NTLM — proof that NTLM continues to be broadly used regardless of its identified weaknesses.
The flaw is exploitable even in environments utilizing NTLM v2, making it a big danger to enterprises who haven’t but moved to Kerberos and are nonetheless counting on NTLM. Considering Microsoft may not patch this issue for a while, enterprise defenders ought to take steps to mitigate the vulnerability of their environments. This Tech Tip outlines how Dynamic Entry Insurance policies, just a few hardening steps, and MFA, might help restrict makes an attempt to take advantage of this vulnerability. Upgrading the protocol, the place doable, might eradicate the problem utterly.
What Is the NTLM Vulnerability?
When a person views a malicious file in Home windows Explorer — whether or not is 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 mechanically downloaded from a malicious internet web page — an outbound NTLM connection is triggered. This causes Home windows to mechanically ship NTLM hashes of the presently logged-in person 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 programs. There may be additionally the danger that attackers can use the uncovered passwords to entry the group’s software-as-a-service 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The basic downside with NTLM lies in its outdated protocol design. NTLM transmits password hashes as an alternative 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 towards relay assaults are key weaknesses that make it extremely exploitable. Furthermore, NTLM authentication doesn’t assist trendy security measures like Multi-Issue Authentication (MFA), leaving programs open to a wide range of credential theft strategies, reminiscent of pass-the-hash and hash relaying.
What Defenders Have to Do
To mitigate this vulnerability, Microsoft has up to date earlier steering on enable Extended Protection for Authentication (EPA) on LDAP, Active Directory Certificate Services (AD CS), and Exchange Server. On Home windows Server 2022 and 2019, directors can manually allow EPA for AD CS and channel binding for LDAP. There are scripts provided by Microsoft to activate EPA manually on Alternate Server 2016. The place doable, 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 because of legacy programs. These groups ought to contemplate extra authentication layers like Dynamic Danger Primarily based Insurance policies for safeguarding present NTLM legacy programs towards exploitations.
Harden LDAP configurations. Configure LDAP to implement channel binding and monitor for legacy shoppers that won’t assist these settings.
Test affect on SaaS. In case you are not sure whether or not there are purposes or shoppers in your surroundings that depend on NTLMv2, you should use Group Coverage to allow the Community Safety: Prohibit NTLM: Audit incoming NTLM visitors coverage setting. This is not going to block NTLMv2 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 establish which consumer purposes, servers, or companies 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: Prohibit NTLM setting will cut back the danger of fallback eventualities the place NTLM is unintentionally used.
Monitor SMB visitors. Enabling SMB signing and encryption might help forestall attackers from impersonating official servers and triggering NTLM authentication. Blocking outbound SMB visitors to untrusted networks may even cut back the danger of NTLM credential leakage to rogue servers. Implement community monitoring and alerting for uncommon SMB visitors patterns, notably outbound requests to unknown or untrusted IP addresses.
Go away NTLM behind. NTLM has been deprecated. Directors ought to audit NTLM utilization to establish which programs nonetheless depend on NTLM. Organizations ought to prioritize transitioning these programs away from NTLM to extra trendy authentication protocols like Kerberos. As soon as a extra trendy protocol is in place, implement multi-factor authentication (MFA) so as to add an extra layer of safety.
Taking these steps will assist organizations deal with the basic flaws in NTLM and enhance their safety posture .
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