Suspicious Dropbox API Usage — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-04-20 / not supplied.

{
  "category": "network_connection",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 8cd27f9c99c20fb10bf79106721856999d27a6fae6768cc743ea6017490339f9

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Suspicious Dropbox API Usage
id: 25eabf56-22f0-4915-a1ed-056b8dae0a68
status: test
description: Detects an executable that isn't dropbox but communicates with the Dropbox API
references:
    - https://app.any.run/tasks/7e906adc-9d11-447f-8641-5f40375ecebb
    - https://www.zscaler.com/blogs/security-research/new-espionage-attack-molerats-apt-targeting-users-middle-east
author: Florian Roth (Nextron Systems)
date: 2022-04-20
tags:
    - attack.command-and-control
    - attack.exfiltration
    - attack.t1105
    - attack.t1567.002
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Initiated: 'true'
        DestinationHostname|endswith:
            - 'api.dropboxapi.com'
            - 'content.dropboxapi.com'
    filter_main_legit_dropbox:
        # Note: It's better to add a specific path to the exact location(s) where dropbox is installed
        Image|contains: '\Dropbox'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Legitimate use of the API with a tool that the author wasn't aware of
level: high

Original YAML and metadata in JSON

False positives

• Legitimate use of the API with a tool that the author wasn't aware of

Source references

• https://app.any.run/tasks/7e906adc-9d11-447f-8641-5f40375ecebb
• https://www.zscaler.com/blogs/security-research/new-espionage-attack-molerats-apt-targeting-users-middle-east