Detections
Explore public detection logic contributed by the community across SIEM and rule languages.
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The following analytic identifies instances where email forwarding has been enabled on mailboxes within an Office 365 environment. It detects this activity by monitoring the Set-Mailbox operation within the o365_management_activity logs, specifically looking for changes to the ForwardingAddress or ForwardingSmtpAddress parameters. This activity is significant as unauthorized email forwarding can lead to data exfiltration and unauthorized access to sensitive information. If confirmed malicious, attackers could intercept and redirect emails, potentially compromising confidential communications and leading to data breaches.
The following analytic identifies when Office 365 users search for suspicious keywords or have an excessive number of queries to a mailbox within a limited timeframe. This behavior may indicate that a malicious actor has gained control of a mailbox and is conducting discovery or enumeration activities.
The following analytic identifies when cross-tenant access/synchronization policies are changed in an Azure tenant. Adversaries have been observed altering victim cross-tenant policies as a method of lateral movement or maintaining persistent access to compromised environments. These policies should be considered sensitive and monitored for changes and/or loose configuration.
This analytic identifies when an Office 365 email recipient receives and then deletes emails related to both password changes and banking/payroll changes within a short period. This behavior may indicate a compromised account where a threat actor is attempting to redirect the victim's payroll to an attacker-controlled bank account. The rule correlates message trace logs with management activity logs to detect the receipt and subsequent deletion of specific types of emails.
This analytic detects when an excessive number of files are accessed from Office 365 by the same user over a short period of time. This behavior may indicate an attacker staging data for exfiltration or an insider threat removing organizational data. The rule specifically looks for `fileaccessed` operations in the Office 365 Universal Audit Log, excluding SharePoint app access and common image file extensions. It then calculates the count of unique source file names accessed per user and flags users whose access count significantly exceeds the average (3 standard deviations above the mean) and is greater than 50 files. This can help identify malicious actors abusing "open in app" functionality or Graph API-based access to evade typical file download events.
The analytic detects the assignment of critical Graph API permissions in Azure AD using the O365 Unified Audit Log. It focuses on permissions such as Application.ReadWrite.All, AppRoleAssignment.ReadWrite.All, and RoleManagement.ReadWrite.Directory. The detection method leverages Azure Active Directory workload events, specifically 'Update application' operations. This activity is significant as these permissions provide extensive control over Azure AD settings, posing a high risk if misused. If confirmed malicious, this could allow unauthorized modifications, leading to potential data breaches or privilege escalation. Immediate investigation is crucial.
This analytic detects the registration of a new Multi-Factor Authentication (MFA) method for a user account within Office 365. It leverages O365 audit logs to identify changes in MFA configurations. This activity is significant as it may indicate an attacker's attempt to maintain persistence on a compromised account. If confirmed malicious, the attacker could bypass existing security measures, solidify their access, and potentially escalate privileges or access sensitive data. Immediate verification and remediation are required to secure the affected account.
The following analytic detects the assignment of the 'full_access_as_app' permission to an application registration in Office 365 Exchange Online. This detection leverages Office 365 management activity logs and filters Azure Active Directory workload events to identify when the specific permission, identified by GUID 'dc890d15-9560-4a4c-9b7f-a736ec74ec40', is granted. This activity is significant because it provides extensive control over Office 365 operations, including access to all mailboxes and the ability to send mail as any user. If confirmed malicious, this could lead to unauthorized data access, exfiltration, or account compromise. Immediate investigation is required.
The analytic detects when emails are accessed in Office 365 Exchange via the Microsoft Graph API using the client ID '00000003-0000-0000-c000-000000000000'. It leverages the 'MailItemsAccessed' operation within the Exchange workload, focusing on OAuth-authenticated applications. This activity is significant as unauthorized access to emails can lead to data breaches and information theft. If confirmed malicious, attackers could exfiltrate sensitive information, compromise user accounts, and further infiltrate the organization's network.
This detection identifies when an Azure Service Principal elevates privileges by adding itself to a new app role assignment. This activity indicates a potential privilege escalation attempt where a service principal grants itself additional permissions, which could lead to unauthorized access or control within the Azure environment.
The following analytic identifies when an O365 email account hard deletes an excessive number of emails within a short period (within 1 hour). This behavior may indicate a compromised account where the threat actor is attempting to permanently purge a large amount of items from the mailbox. Threat actors may attempt to remove evidence of their activity by purging items from the compromised mailbox. Some account owner legitimate behaviors can trigger this alert, however these actions may not be aligned with organizational expectations / best practice behaviors.
The following analytic detects when high-privilege roles such as "Exchange Administrator," "SharePoint Administrator," or "Global Administrator" are granted within Office 365. It leverages O365 audit logs to identify events where these roles are assigned to any user or service account. This activity is significant for SOCs as these roles provide extensive permissions, allowing broad access and control over critical resources and data. If confirmed malicious, this could enable attackers to gain significant control over O365 resources, access, modify, or delete critical data, and compromise the overall security and functionality of the O365 environment.
The analytic identifies instances where a user grants consent to an application requesting mail-related permissions within the Office 365 environment. It leverages O365 audit logs, specifically focusing on events related to application permissions and user consent actions. This activity is significant as it can indicate potential security risks, such as data exfiltration or spear phishing, if malicious applications gain access. If confirmed malicious, this could lead to unauthorized data access, email forwarding, or sending malicious emails from the compromised account. Validating the legitimacy of the application and consent context is crucial to prevent data breaches.
This analytic identifies when the allowed domain settings for O365 SharePoint have been changed. With Azure AD B2B collaboration, users and administrators can invite external users to collaborate with internal users. External guest account invitations may also need access to OneDrive/SharePoint resources. These changes should be monitored by security teams as they could potentially lead to unauthorized access.
The analytic detects the assignment of the 'full_access_as_app' permission to an application within Office 365 Exchange Online. This is identified by the GUID 'dc890d15-9560-4a4c-9b7f-a736ec74ec40' and the ResourceAppId '00000002-0000-0ff1-ce00-000000000000'. The detection leverages the azure_monitor_aad data source, focusing on AuditLogs with the operation name 'Update application'. This activity is significant as it grants broad control over Office 365 operations, including full access to all mailboxes and the ability to send emails as any user. If malicious, this could lead to unauthorized access and data exfiltration.
The following analytic identifies instances where new IP addresses are added to the trusted IPs list in Office 365, potentially allowing users from these IPs to bypass Multi-Factor Authentication (MFA) during login. It leverages O365 audit logs, specifically focusing on events related to the modification of trusted IP settings. This activity is significant because adding trusted IPs can weaken the security posture by bypassing MFA, which is a critical security control. If confirmed malicious, this could lead to unauthorized access, compromising sensitive information and systems. Immediate investigation is required to validate the legitimacy of the IP addition.
The analytic detects when a high number of Office 365 Exchange mailboxes are accessed via API (Microsoft Graph API or Exchange Web Services) within a short timeframe. It leverages 'MailItemsAccessed' operations in Exchange, using AppId and regex to identify API interactions. This activity is significant as it may indicate unauthorized mass email access, potentially signaling data exfiltration or account compromise. If confirmed malicious, attackers could gain access to sensitive information, leading to data breaches and further exploitation of compromised accounts. The threshold is set to flag over five unique mailboxes accessed within 10 minutes, but should be tailored to your environment.
This analytic identifies the assignment of sensitive and privileged Azure Active Directory roles to an Azure AD user. Adversaries and red teams alike may assign these roles to a compromised account to establish Persistence in an Azure AD environment. This detection leverages the O365 Universal Audit Log data source.
The following analytic detects when the "risk-based step-up consent" security setting in Microsoft 365 is disabled. It monitors Azure Active Directory logs for the "Update authorization policy" operation, specifically changes to the "AllowUserConsentForRiskyApps" setting. This activity is significant because disabling this feature can expose the organization to OAuth phishing threats, allowing users to grant consent to malicious applications. If confirmed malicious, attackers could gain unauthorized access to user data and sensitive information, leading to data breaches and further compromise within the organization.
The following analytic identifies when an O365 email recipient receives and then deletes emails related to password or banking/payroll changes within a short period. This behavior may indicate a compromised account where the threat actor is attempting to redirect the victims payroll to an attacker controlled bank account.
This analytic detects when an excessive number of files are synced from Office 365 by the same user over a short period of time. This behavior may indicate an attacker staging data for exfiltration or an insider threat removing organizational data. The rule specifically looks for `filesyncdownload*` operations with a `UserAgent` containing `*SkyDriveSync*` and filters out cases where the `SiteUrl` matches the user's flat ID, which could be legitimate personal sync activity. A threshold of more than 50 unique source file names downloaded by a single user is used to trigger the alert. Additional attention should be taken with any Azure Guest (#EXT#) accounts.
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