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#AZURE ACTIVE DIRECTORY DOMAIN SERVICES LIMITATIONS PASSWORD#
Although, users without an Azure AD password remain unaffected.īecause the success of a brute-force attack is largely dependent on password strength, Secureworks has rated the flaw as "Medium" severity in its writeup.Īt the time of writing, there are no known fixes or workarounds to block the use of the usernamemixed endpoint. "Threat actors can exploit the autologon usernamemixed endpoint in any Azure AD or Microsoft 365 organization, including organizations that use Pass-through Authentication (PTA)," explain the researchers. The flaw is not limited to organizations using Seamless SSO. Microsoft indicates that the usernamemixed endpoint is only required for legacy Office clients that predate the Office 20 update." Exploitation not limited to organizations using SSO
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However, that access is required for Seamless SSO. "Microsoft AD FS documentation recommends disabling internet access to the windowstransport endpoint. " analysis indicates that the autologon service is implemented with Azure Active Directory Federation Services (AD FS)," explain the CTU researchers.
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This is why having no visibility into the failed sign-in attempts is a problem. Secureworks researchers state that most security tools and countermeasures aimed at detecting brute-force or password spraying attacks rely on sign-in event logs and look for specific error codes. The AADSTS error codes used during Azure AD authentication workflow are shown below: AADSTS50034 The user does not existĪADSTS50053 The user exists and the correct username and password were entered, but the account is lockedĪADSTS50056 The user exists but does not have a password in Azure ADĪADSTS50126 The user exists, but the wrong password was enteredĪADSTS80014 The user exists, but the maximum Pass-through Authentication time was exceeded This omission allows threat actors to utilize the usernamemixed endpoint for undetected brute-force attacks," explain CTU researchers in their writeup. However, autologon's authentication to Azure AD is not logged. "Successful authentication events generate sign-ins logs. This month, Secureworks is alerting its customers to the flaw, according to a communication shared with Ars by a source. The same month, Secureworks reported the flaw to Microsoft that then confirmed this behavior existed by July but decided it was "by design." "This flaw allows threat actors to perform single-factor brute-force attacks against Azure Active Directory without generating sign-in events in the targeted organization's tenant," explain the researchers.
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In June this year, researchers at Secureworks Counter Threat Unit (CTU) discovered a flaw in the protocol used by Azure Active Directory Seamless Single Sign-On service. And, these attempts aren't logged on to the server. That would make an ideal scenario for a stealthy threat actor-leaving server admins with little to no visibility into the attacker's actions, let alone the possibility of blocking them.Ī newly discovered bug in Microsoft Azure's Active Directory (AD) implementation allows just that: single-factor brute-forcing of a user's AD credentials. Imagine having unlimited attempts to guess someone's username and password without getting caught.