After a security breach, forensic investigators work quickly to follow the attacker’s trail. Security experts have analyzed this situation and found that a key source of evidence is often overlooked: Microsoft Azure Storage logs.

While frequently overlooked, these logs provide invaluable insights that can help reconstruct an attack, trace data theft, and identify security gaps.

Azure Storage Accounts, which can hold vast amounts of sensitive data, are a prime target for threat actors aiming to exfiltrate information.

However, the diagnostic logging that captures their malicious activity is not always enabled by default, creating a significant blind spot for incident response teams. Without these logs, crucial evidence of how attackers accessed and stole data can be lost forever.

Threat actors exploit various weaknesses to gain unauthorized access, including misconfigured security settings, weak access controls, and leaked credentials.

Two common methods involve the misuse of Shared Access Signature (SAS) tokens, which grant specific permissions for a limited time, and the exposure of Storage Account keys, which provide privileged, long-term access to the data, Microsoft said.

Microsoft Azure Storage Logs For Forensic

Once logging is enabled correctly, investigators can turn to the StorageBlobLogs table within Azure’s Log Analytics.

These logs capture essential details about every read, write, and delete operation on stored data. Key fields provide a digital breadcrumb trail of the attacker’s actions:

• OperationName: Identifies the specific action taken, such as “GetBlob” (downloading a file), “PutBlob” (uploading a file), or “DeleteBlob.”
• CallerIpAddress: Reveals the IP address of the requester, helping to pinpoint the origin of the malicious activity.
• UserAgentHeader: Offers clues about the tools used to access the data, distinguishing between access from a web browser, the Azure portal, or specialized tools like AzCopy or Azure Storage Explorer.
• AuthenticationType: Shows how the user authenticated, whether through standard credentials (OAuth), a SAS token, or an Account Key.

By analyzing these fields, investigators can differentiate between legitimate user activity and a threat actor’s movements.

For example, a sudden spike in “ListContainers” or “ListBlobs” operations from an unknown IP address could indicate an attacker is mapping out the storage environment.

Similarly, tracking “GetBlob” operations can confirm data exfiltration and identify exactly which files were accessed.

From Detection to Prevention

The investigation often starts by correlating suspicious sign-ins from Microsoft Entra ID with activity in the storage logs. In one scenario, a compromised user account with administrative privileges might be used to grant another malicious account access roles like “Storage Blob Data Contributor.”

The AzureActivity logs would show this role assignment, while the StorageBlobLogs logs would subsequently reveal the new account accessing and downloading sensitive files.

By correlating the authentication hash of a SAS token, investigators can track every action performed with that token, even if the attacker switches IP addresses. This helps define the full scope of the compromise.

Dreymann and Shiva P’s analysis underscores a critical message for organizations using Azure: enabling storage account logging is not just an option but a necessity.

These logs are indispensable for post-breach forensics, allowing teams to understand the incident’s scope, guide remediation efforts, and implement stronger controls to prevent future data theft.

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