Adversaries may patch, modify, or otherwise backdoor cloud authentication processes that are tied to on-premises user identities in order to bypass typical authentication mechanisms, access credentials, and enable persistent access to accounts.
Many organizations maintain hybrid user and device identities that are shared between on-premises and cloud-based environments. These can be maintained in a number of ways. For example, Azure AD includes three options for synchronizing identities between Active Directory and Azure AD:
AD FS can also be used with other SaaS and cloud platforms such as AWS and GCP, which will hand off the authentication process to AD FS and receive a token containing the hybrid users’ identity and privileges.
By modifying authentication processes tied to hybrid identities, an adversary may be able to establish persistent privileged access to cloud resources. For example, adversaries who compromise an on-premises server running a PTA agent may inject a malicious DLL into the
AzureADConnectAuthenticationAgentService process that authorizes all attempts to authenticate to Azure AD, as well as records user credentials. In environments using AD FS, an adversary may edit the
Microsoft.IdentityServer.Servicehost configuration file to load a malicious DLL that generates authentication tokens for any user with any set of claims, thereby bypassing multi-factor authentication and defined AD FS policies.
In some cases, adversaries may be able to modify the hybrid identity authentication process from the cloud. For example, adversaries who compromise a Global Administrator account in an Azure AD tenant may be able to register a new PTA agent via the web console, similarly allowing them to harvest credentials and log into the Azure AD environment as any user.
AADInternals can inject a malicious DLL (
APT29 has edited the
Periodically review the hybrid identity solution in use for any discrepancies. For example, review all PTA agents in the Azure Management Portal to identify any unwanted or unapproved ones. If ADFS is in use, review DLLs and executable files in the AD FS and Global Assembly Cache directories to ensure that they are signed by Microsoft. Note that in some cases binaries may be catalog-signed, which may cause the file to appear unsigned when viewing file properties.
Integrating multi-factor authentication (MFA) as part of organizational policy can greatly reduce the risk of an adversary gaining control of valid credentials that may be used for additional tactics such as initial access, lateral movement, and collecting information. MFA can also be used to restrict access to cloud resources and APIs.
|M1026||Privileged Account Management||
Limit on-premises accounts with access to the hybrid identity solution in place. For example, limit Azure AD Global Administrator accounts to only those required, and ensure that these are dedicated cloud-only accounts rather than hybrid ones.
|ID||Data Source||Data Component||Detects|
|DS0015||Application Log||Application Log Content||
Enable security auditing to collect logs from hybrid identity solutions. For example, monitor sign-ins to the Azure AD Application Proxy Connector, which are typically generated only when a new PTA Agent is added.  If AD FS is in use, review the logs for event ID 501, which specifies all EKU attributes on a claim, and raise alerts on any values that are not configured in your environment.
Monitor for suspicious modification of files associated with hybrid identity authentication processes, such as configuration files. Monitor for access to certificates and cryptographic keys material.
|DS0028||Logon Session||Logon Session Creation||
Monitor for discrepancies in authentication to cloud services, such as PTA sign-ins recorded in Azure AD that lack corresponding events in AD.
Monitor the hybrid identity solution in use for the loading of unauthorized DLLs. For example, monitor all PTA agent servers for the creation of DLLs as well as the loading of DLLs into the