CTD-000118

AD domain with multiple failed authentication attempts from invalid users via NTLM

High
Active Directory
Initial Access
v12

Signature Identity

CTD-000118
Threat ID
12
Version
IOA-IOC
Indicator Type

Threat Description

Multiple failed authentication attempts from invalid users via NTLM might be an indication of a threat actor performing a Password Spraying attack against an Active Directory environment to obtain initial access or elevate privileges. Detection mechanism uses the event 4776 and error code 0xC0000064 meaning that `The username you typed does not exist` (the attempted user is a legitimate domain user).

NOTE: This threat rule includes a built-in lookback parameter set to 25 hours. Only events that occurred within this timeframe are processed by the rule.

MITRE ATT&CK: Attack Tactics

Initial Access

D3FEND: Defend Tactics

Local Account Monitoring

Remediation

  1. To reset the password of a user affected by Password Spray attack using ADUC (Active Directory Users and Computers):
    1. Run the ADUC console (dsa.msc).
    2. Search for the user account in the AD domain.
    3. Right-click on it.
    4. Select Reset password.
    5. You can search by right-clicking the domain and selecting Find, or by navigating to the user’s location in AD.
    6. In the Reset Password dialog, enter the new password and confirm it. You can also check the option to force the user to change the password at the next logon.
    7. Click OK.
  2. To eliminate easily guessed passwords, configure Microsoft Entra Password Protection. This capability includes a globally banned password list that Microsoft maintains and updates. You can also block a custom list of passwords that are relevant to your region or company. Once enabled, users won’t be able to choose a password on either of these lists, making it significantly less likely that an adversary can guess a user’s password. You can also use this feature to define how many sign-in attempts will trigger a lockout and how long the lockout will last. Learn more: Deploy on-premises Microsoft Entra Password Protection – Microsoft Entra ID | Microsoft Learn.
  3. The best way to reduce your risk of password spray is to eliminate passwords entirely. Solutions like Windows Hello or FIDO2 security keys let users sign in using biometrics and/or a physical key or device. Get started by enabling Mult-Factor Authentication (MFA) across all your accounts. MFA requires that users sign in with at least two authentication factors: something they know (like a password or PIN), something they are (such as biometrics), and/or something they have (such as a trusted device).

Frequently Asked Questions

What does AD domain with multiple failed authentication attempts from invalid users via NTLM mean?

Repeated, unsuccessful login attempts using the NTLM protocol from unknown or unauthorized users indicate potential malicious activity. This behavior is often associated with a Password Spraying attack.

This condition is rated high severity because it indicates an attacker may be attempting to gather information for a targeted attack, potentially leading to unauthorized access or privilege escalation in the Active Directory environment. The repeated attempts provide valuable reconnaissance data, allowing attackers to refine their attacks and increase their chances of success.

Attackers can use collected data to plan a more targeted attack. They may attempt to create a valid username and password combination or exploit other vulnerabilities in the environment using the gathered information, ultimately leading to unauthorized access or privilege escalation.

Cayosoft Guardian continuously monitors Active Directory event logs for repeated, unsuccessful login attempts using the NTLM protocol. When this activity is detected, Guardian flags it as a security issue to prompt administrators to investigate and mitigate the threat.

Cayosoft Guardian provides real-time visibility into potential security threats, alerting administrators to take prompt action. This enables teams to quickly investigate and respond to suspicious activity, reducing the likelihood of successful attacks and minimizing the attacker's ability to persist in the environment.

Stop AD Threats As They Happen

Cayosoft Protector provides continuous monitoring and real-time alerts across your entire Microsoft Identity stack

Classification
Systems
Active Directory
Themes
Account protection NTLM Password Spraying
Attack Tactics
Initial Access
Defend Tactics
Local Account Monitoring
Indicator Types
IOA IOC
Related Threats
CTD-000139
Kerberos Constrained Delegation: krbtgt Risks
Critical
CTD-000122
Active Directory Schema Update Permission Risks
Critical