Detections
Explore public detection logic contributed by the community across SIEM and rule languages.
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This query looks for users accessing multiple other users' mailboxes, or accessing multiple folders in another user's mailbox.
This query is inspired by an Azure Sentinel detection.
Reference - https://github.com/Azure/Azure-Sentinel/blob/master/Hunting%20Queries/OfficeActivity/AnomolousUserAccessingOtherUsersMailbox.yaml
This query is inspired by an Azure Sentinel detection.
Reference - https://github.com/Azure/Azure-Sentinel/blob/master/Hunting%20Queries/OfficeActivity/AnomolousUserAccessingOtherUsersMailbox.yaml
This query was originally published in the threat analytics report, MailSniper Exchange attack tool.
MailSniper is a tool that targets Microsoft Exchange Server. The core function is to connect to Exchange Server and search through emails. In support of this, it can perform reconnaissance, collection, exfiltration, and credential theft. MailSniper is used both by red teams running penetration tests, and by malicious actors.
Microsoft Defender Security Center may record the following alerts during and after an attack:
1. Global mail search on Exchange using MailSniper
2. Exchange mailbox or mail folder search using MailSniper
3. Enumeration of Active Directory usernames using MailSniper
4. Enumeration of the Exchange GAL using MailSniper
5. Access to Exchange inboxes using MailSniper
6. Password spraying using MailSniper
7. Enumeration of domains and user accounts using MailSniper
The following query detects activity commonly associated with attacks run with MailSniper.
Reference - https://github.com/dafthack/MailSniper
MailSniper is a tool that targets Microsoft Exchange Server. The core function is to connect to Exchange Server and search through emails. In support of this, it can perform reconnaissance, collection, exfiltration, and credential theft. MailSniper is used both by red teams running penetration tests, and by malicious actors.
Microsoft Defender Security Center may record the following alerts during and after an attack:
1. Global mail search on Exchange using MailSniper
2. Exchange mailbox or mail folder search using MailSniper
3. Enumeration of Active Directory usernames using MailSniper
4. Enumeration of the Exchange GAL using MailSniper
5. Access to Exchange inboxes using MailSniper
6. Password spraying using MailSniper
7. Enumeration of domains and user accounts using MailSniper
The following query detects activity commonly associated with attacks run with MailSniper.
Reference - https://github.com/dafthack/MailSniper
Identifies anomalous increases in Exchange mail items accessed operations.
The query leverages KQL built-in anomaly detection algorithms to find large deviations from baseline patterns.
Sudden increases in execution frequency of sensitive actions should be further investigated for malicious activity.
Manually change scorethreshold from 1.5 to 3 or higher to reduce the noise based on outliers flagged from the query criteria.
Read more about MailItemsAccessed- https://docs.microsoft.com/microsoft-365/compliance/advanced-audit?view=o365-worldwide#mailitemsaccessed
Query insprired by Azure Sentinel detection https://github.com/Azure/Azure-Sentinel/blob/master/Detections/OfficeActivity/MailItemsAccessedTimeSeries.yaml
The query leverages KQL built-in anomaly detection algorithms to find large deviations from baseline patterns.
Sudden increases in execution frequency of sensitive actions should be further investigated for malicious activity.
Manually change scorethreshold from 1.5 to 3 or higher to reduce the noise based on outliers flagged from the query criteria.
Read more about MailItemsAccessed- https://docs.microsoft.com/microsoft-365/compliance/advanced-audit?view=o365-worldwide#mailitemsaccessed
Query insprired by Azure Sentinel detection https://github.com/Azure/Azure-Sentinel/blob/master/Detections/OfficeActivity/MailItemsAccessedTimeSeries.yaml
This query correlates Microsoft Defender for Office 365 signals and Microsoft Entra ID identity data to find the relevant endpoint event BrowerLaunchedToOpen in Microsoft Defender ATP.
This event reflects relevant clicks on the malicious URL in the spear-phishing email recognized by Microsoft Defender for Office 365.
This event reflects relevant clicks on the malicious URL in the spear-phishing email recognized by Microsoft Defender for Office 365.
The MailItemsAccessed action is part of the new Advanced Audit functionality of Microsoft Defender XDR. It's part of Exchange mailbox auditing and is enabled by default for users that have an Office 365 or Microsoft 365 E5 license, or for organizations with a Microsoft 365 E5 Compliance add-on subscription.
If more than 1,000 MailItemsAccessed audit records are generated in less than 24 hours, Exchange Online will stop generating auditing records for MailItemsAccessed activity. When a mailbox is throttled, MailItemsAccessed activity will not be logged for 24 hours after the mailbox was throttled. If this occurs, there's a potential that mailbox could have been compromised during this period. The recording of MailItemsAccessed activity will be resumed following a 24-hour period.
The query is looking for MailItemsAccessed Throttling events where the operation is done by a ClientApplication.
See The MailItemsAccessed mailbox auditing action.
Reference - https://docs.microsoft.com/microsoft-365/compliance/mailitemsaccessed-forensics-investigations?view=o365-worldwide#the-mailitemsaccessed-mailbox-auditing-action
If more than 1,000 MailItemsAccessed audit records are generated in less than 24 hours, Exchange Online will stop generating auditing records for MailItemsAccessed activity. When a mailbox is throttled, MailItemsAccessed activity will not be logged for 24 hours after the mailbox was throttled. If this occurs, there's a potential that mailbox could have been compromised during this period. The recording of MailItemsAccessed activity will be resumed following a 24-hour period.
The query is looking for MailItemsAccessed Throttling events where the operation is done by a ClientApplication.
See The MailItemsAccessed mailbox auditing action.
Reference - https://docs.microsoft.com/microsoft-365/compliance/mailitemsaccessed-forensics-investigations?view=o365-worldwide#the-mailitemsaccessed-mailbox-auditing-action
This query helps report on who Previewed/Downloaded email messages using the Email entity page in Defender for Office 365
This query helps report on email access by administrators
Use this query to find email stealing activities ran by Qakbot that will use "ping.exe -t 127.0.0.1" to obfuscate subsequent actions.
Email theft that occurs might be exfiltrated to operators and indicates that the malware completed a large portion of its automated activity without interruption.
Email theft that occurs might be exfiltrated to operators and indicates that the malware completed a large portion of its automated activity without interruption.
The analytic detects when emails are accessed in Office 365 Exchange via Exchange Web Services (EWS) using OAuth-authenticated applications. It leverages the ClientInfoString field to identify EWS interactions and aggregates metrics such as access counts, timing, and client IP addresses, categorized by user, ClientAppId, OperationCount, and AppId. Monitoring OAuth applications accessing emails through EWS is crucial for identifying potential abuse or unauthorized data access. If confirmed malicious, this activity could lead to unauthorized email access, data exfiltration, or further compromise of sensitive information.
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 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.
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.
The following analytic detects instances where the inbox folder of an Office 365 mailbox is shared with all users within the tenant. It leverages Office 365 management activity events to identify when the 'Inbox' folder permissions are modified to include 'Everyone' with read rights. This activity is significant as it represents a potential security risk, allowing unauthorized access to sensitive emails. If confirmed malicious, this could lead to data breaches, exfiltration of confidential information, and further compromise through spear-phishing or other malicious activities based on the accessed email content.
The analytic identifies a significant increase in data transfers from an email server to client hosts. It uses statistical analysis on network traffic to detect anomalies based on average and standard deviation of outbound bytes. This activity is significant as it may indicate a malicious actor exfiltrating data via the email server, potentially leading to unauthorized data access and breaches.
The following analytic detects the execution of known MailSniper PowerShell functions on a machine. It leverages PowerShell logs (EventCode 4104) to identify specific script block text associated with MailSniper activities. This behavior is significant as MailSniper is often used by attackers to harvest sensitive emails from compromised Exchange servers. If confirmed malicious, this activity could lead to unauthorized access to sensitive email data, credential theft, and further compromise of the email infrastructure.
The analytic identifies hosts receiving an unusually high volume of network traffic from an email server. It leverages the Network_Traffic data model to sum incoming bytes to clients from email servers, comparing current traffic against historical averages and standard deviations. This activity is significant as it may indicate data exfiltration by a malicious actor using the email server. If confirmed malicious, this could lead to unauthorized data access and potential data breaches, compromising sensitive information and impacting organizational security.
This analytic identifies instances where the Mail.Read Graph API permissions are granted to an application registration within an Office 365 tenant. It leverages O365 audit logs, specifically events related to changes in application permissions within the AzureActiveDirectory workload. This activity is significant because the Mail.Read permission allows applications to access and read all emails within a user's mailbox, which often contain sensitive or confidential information. If confirmed malicious, this could lead to data exfiltration, spear-phishing attacks, or further compromise based on the information gathered from the emails.
The analytic identifies when the results of a content search within the Office 365 Security and Compliance Center are exported. It uses the SearchExported operation from the SecurityComplianceCenter workload in the o365_management_activity data source. This activity is significant because exporting search results can involve sensitive or critical organizational data, potentially leading to data exfiltration. If confirmed malicious, an attacker could gain access to and exfiltrate sensitive information, posing a severe risk to the organization's data security and compliance posture.
The analytic identifies when a user with sufficient access to the O365 Security & Compliance portal uses premium investigation features (Threat Explorer) to directly view email. Adversaries may exploit privileged access with this premium feature to enumerate or exfiltrate sensitive data.
The following analytic detects when a content search is initiated within the Office 365 Security and Compliance Center. It leverages the SearchCreated operation from the o365_management_activity logs under the SecurityComplianceCenter workload. This activity is significant as it may indicate an attempt to access sensitive organizational data, including emails and documents. If confirmed malicious, this could lead to unauthorized data access, potential data exfiltration, and compliance violations. Monitoring this behavior helps ensure the integrity and security of organizational data.
Identify when mailboxes are being accessed with requests for N number of messages
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