Introduction to Microsoft Defender for Storage
Microsoft Defender for Storage is an Azure-native layer of security intelligence that detects unusual and potentially harmful attempts to access or exploit your storage accounts. It uses advanced threat detection capabilities and Microsoft Threat Intelligence data to provide contextual security alerts. Those alerts also include steps to mitigate the detected threats and prevent future attacks.
You can enable Microsoft Defender for Storage at either the subscription level (recommended) or the resource level.
Defender for Storage continually analyzes the telemetry stream generated by the Azure Blob Storage and Azure Files services. When potentially malicious activities are detected, security alerts are generated. These alerts are displayed in Microsoft Defender for Cloud together with the details of the suspicious activity along with the relevant investigation steps, remediation actions, and security recommendations.
Analyzed telemetry of Azure Blob Storage includes operation types such as Get Blob, Put Blob, Get Container ACL, List Blobs, and Get Blob Properties. Examples of analyzed Azure Files operation types include Get File, Create File, List Files, Get File Properties, and Put Range.
Defender for Storage doesn't access the Storage account data and has no impact on its performance.
|Release state:||General availability (GA)|
|Pricing:||Microsoft Defender for Storage is billed as shown on the pricing page|
|Protected storage types:||Blob Storage (Standard/Premium StorageV2, Block Blobs)
Azure Files (over REST API and SMB)
Azure Data Lake Storage Gen2 (Standard/Premium accounts with hierarchical namespaces enabled)
Azure China 21Vianet
Connected AWS accounts
What are the benefits of Microsoft Defender for Storage?
Defender for Storage provides:
- Azure-native security - With 1-click enablement, Defender for Storage protects data stored in Azure Blob, Azure Files, and Data Lakes. As an Azure-native service, Defender for Storage provides centralized security across all data assets that are managed by Azure and is integrated with other Azure security services such as Microsoft Sentinel.
- Rich detection suite - Powered by Microsoft Threat Intelligence, the detections in Defender for Storage cover the top storage threats such as unauthenticated access, compromised credentials, social engineering attacks, data exfiltration, privilege abuse, and malicious content.
- Response at scale - Defender for Cloud's automation tools make it easier to prevent and respond to identified threats. Learn more in Automate responses to Defender for Cloud triggers.
Security threats in cloud-based storage services
Microsoft security researchers have analyzed the attack surface of storage services. Storage accounts can be subject to data corruption, exposure of sensitive content, malicious content distribution, data exfiltration, unauthorized access, and more.
The potential security risks are described in the threat matrix for cloud-based storage services and are based on the MITRE ATT&CK® framework, a knowledge base for the tactics and techniques employed in cyber attacks.
What kind of alerts does Microsoft Defender for Storage provide?
Security alerts are triggered for the following scenarios (typically from 1-2 hours after the event):
|Type of threat||Description|
|Unusual access to an account||For example, access from a TOR exit node, suspicious IP addresses, unusual applications, unusual locations, and anonymous access without authentication.|
|Unusual behavior in an account||Behavior that deviates from a learned baseline, such as a change of access permissions in an account, unusual access inspection, unusual data exploration, unusual deletion of blobs/files, or unusual data extraction.|
|Hash reputation based Malware detection||Detection of known malware based on full blob/file hash. This can help detect ransomware, viruses, spyware, and other malware uploaded to an account, prevent it from entering the organization, and spreading to more users and resources. See also Limitations of hash reputation analysis.|
|Unusual file uploads||Unusual cloud service packages and executable files that have been uploaded to an account.|
|Public visibility||Potential break-in attempts by scanning containers and pulling potentially sensitive data from publicly accessible containers.|
|Phishing campaigns||When content that's hosted on Azure Storage is identified as part of a phishing attack that's impacting Microsoft 365 users.|
Alerts include details of the incident that triggered them, and recommendations on how to investigate and remediate threats. Alerts can be exported to Microsoft Sentinel or any other third-party SIEM or any other external tool. Learn more in Stream alerts to a SIEM, SOAR, or IT Service Management solution.
For a comprehensive list of all Defender for Storage alerts, see the alerts reference page. This is useful for workload owners who want to know what threats can be detected and help SOC teams gain familiarity with detections before investigating them. Learn more about what's in a Defender for Cloud security alert, and how to manage your alerts in Manage and respond to security alerts in Microsoft Defender for Cloud.
Limitations of hash reputation analysis
Hash reputation isn't deep file inspection - Microsoft Defender for Storage uses hash reputation analysis supported by Microsoft Threat Intelligence to determine whether an uploaded file is suspicious. The threat protection tools don’t scan the uploaded files; rather they analyze the telemetry generated from the Blobs Storage and Files services. Defender for Storage then compares the hashes of newly uploaded files with hashes of known viruses, trojans, spyware, and ransomware.
Hash reputation analysis isn't supported for all files protocols and operation types - Some, but not all, of the telemetry logs contain the hash value of the related blob or file. In some cases, the telemetry doesn't contain a hash value. As a result, some operations can't be monitored for known malware uploads. Examples of such unsupported use cases include SMB file-shares and when a blob is created using Put Block and Put Block List.
When a file is suspected to contain malware, Defender for Cloud displays an alert and can optionally email the storage owner for approval to delete the suspicious file. To set up this automatic removal of files that hash reputation analysis indicates contain malware, deploy a workflow automation to trigger on alerts that contain "Potential malware uploaded to a storage account”.
Enable Defender for Storage
When you enable this Defender plan on a subscription, all existing Azure Storage accounts will be protected and any storage resources added to that subscription in the future will also be automatically protected.
You can enable Defender for Storage in any of several ways, described in Set up Microsoft Defender for Cloud in the Azure Storage documentation.
Trigger a test alert for Microsoft Defender for Storage
To test the security alerts from Microsoft Defender for Storage in your environment, generate the alert "Access from a Tor exit node to a storage account" with the following steps:
Open a storage account with Microsoft Defender for Storage enabled.
From the sidebar, select “Containers” and open an existing container or create a new one.
Upload a file to that container.
Don't upload a file containing sensitive data.
Use the context menu on the uploaded file to select “Generate SAS”.
Leave the default options and select Generate SAS token and URL.
Copy the generated SAS URL.
On your local machine, open the Tor browser.
You can download Tor from the Tor Project site https://www.torproject.org/download/.
In the Tor browser, navigate to the SAS URL.
Download the file you uploaded in step 3.
Within two hours you'll get the following security alert from Defender for Cloud:
FAQ - Microsoft Defender for Storage
- How do I estimate charges at the account level?
- Can I exclude a specific Azure Storage account from a protected subscription?
- How do I configure automatic responses for security alerts?
How do I estimate charges at the account level?
To optimize costs, you might want to exclude specific Storage accounts associated with high traffic from Defender for Storage protections. To get an estimate of Defender for Storage costs, use the Price Estimation Dashboard.
Can I exclude a specific Azure Storage account from a protected subscription?
To exclude a specific Storage account when Defender for Storage is enabled on a subscription, follow the instructions in Exclude a storage account from Microsoft Defender for Storage protections.
How do I configure automatic responses for security alerts?
Use workflow automation to trigger automatic responses to Defender for Cloud security alerts.
For example, you can set up automation to open tasks or tickets for specific personnel or teams in an external task management system.
Use automation for automatic response - to define your own or use ready-made automation from the community (such as removing malicious files upon detection). For more solutions, visit the Microsoft community on GitHub.
In this article, you learned about Microsoft Defender for Storage.
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