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AWS API Activity from Uncommon S3 Client by Rare User

Identifies AWS API activity originating from uncommon desktop client applications based on the user agent string. This rule detects S3 Browser and Cyberduck, which are graphical S3 management tools that provide bulk…

Description

Identifies AWS API activity originating from uncommon desktop client applications based on the user agent string. This rule detects S3 Browser and Cyberduck, which are graphical S3 management tools that provide bulk upload/download capabilities. While legitimate, these tools are rarely used in enterprise environments and have been observed in use by threat actors for data exfiltration. Any activity from these clients should be validated against authorized data transfer workflows.

Detection logic

Its licence does not clear it for publishing here

Sunturai publishes a detection's own text where the licence it arrived under has been reviewed and permits it, and Elastic License 2.0 has not. The query as its source wrote it, its canonical form and the hash that pins this revision are in the workspace record.

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Detection requirements

Platform
ESXiIaaSLinuxmacOSOffice SuiteSaaSWindows

The rule states no platform. This is derived from the 2 ATT&CK techniques it maps to.

Log source category
event_index

Known benign triggers

  • Some organizations may have legitimate use cases for S3 Browser or Cyberduck, particularly in development, data migration, or backup scenarios. Verify whether the IAM principal, source network, and accessed buckets align with approved workflows. Unexpected activity from these clients, especially accessing sensitive buckets, should be investigated.

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