Data Exfiltration via Personal Cloud

Layer 7: Application Medium risk

How it works

Staff sometimes move work files to personal cloud storage or email so they can work from home, share with someone outside the company, or keep copies after leaving. Attackers who have compromised an account may do the same, using common cloud services because that traffic looks normal and is rarely blocked. Copying files to a personal USB drive or printing them for home use raises many of the same concerns.

Once data leaves approved systems, the organization loses track of who can access it, how long it is kept and whether it is protected. A personal account with a weak password or a public sharing link can expose client records or financial data. For organizations subject to privacy laws, such transfers can lead to a reportable breach even when no harm was intended.

Warning signs

• Uploads to personal cloud or file sharing sites from work devices
• Emails with attachments sent to personal addresses
• Large data transfers before an employee departs
• Unapproved sync apps installed on work computers
• Public sharing links on sensitive files

How to defend against it

• Provide approved, easy-to-use tools for sharing and remote work
• Apply data loss prevention and sensitivity labels
• Block or monitor unapproved cloud storage services
• Restrict external sharing settings in Microsoft 365
• Set clear acceptable use policies and explain why

If it happens to you

1. Identify what data was moved and where it went
2. Request deletion and confirmation from the person involved
3. Revoke sharing links and access where possible
4. Assess privacy breach reporting obligations