Microsoft Copilot for Work Leaks User Files to External Servers
Microsoft Copilot for Work was found to unintentionally exfiltrate user files to external servers, affecting Microsoft 365 customers and raising immediate concerns about data confidentiality, compliance, and the expanding attack surface of AI‑assisted productivity tools.
What is Microsoft Copilot for Work and how does it integrate with Microsoft 365?
Copilot for Work is an AI‑driven assistant embedded in the Microsoft 365 suite, offering contextual suggestions in Word, Excel, Outlook, and Teams. It leverages large language models hosted in Microsoft’s cloud to process user prompts and generate content on the fly. By design, it streams snippets of user data to the AI service so the model can produce relevant output.
How was the file exfiltration discovered?
The issue surfaced in a Reddit discussion on r/netsec, where a security researcher shared network logs showing outbound connections from a Copilot‑enabled tenant to unfamiliar IP ranges. The logs captured file‑level metadata being sent alongside API calls, suggesting that documents were being transmitted beyond the organization’s perimeter.
Why does the exfiltration happen – what technical mechanism is involved?
Copilot’s architecture requires it to send user content to Microsoft’s inference endpoints for analysis. In the observed scenario, the service forwarded entire file payloads rather than just the minimal context needed for generation. This over‑sharing triggered outbound traffic that bypassed typical corporate egress controls, effectively leaking data to Microsoft’s AI back‑end.
Which data types are most likely to be exposed?
Because Copilot is invoked from across the Office suite, any document opened in Word, spreadsheet in Excel, or email drafted in Outlook can be captured. The Reddit logs indicated that PDFs, DOCX files, and even encrypted attachments were part of the outbound stream, meaning confidential contracts, personal data, and intellectual property are at risk.
Who is affected – which organizations and users?
Any Microsoft 365 tenant that has enabled Copilot for Work is potentially exposed. Large enterprises, midsize businesses, and even educational institutions that rely on AI‑enhanced collaboration tools may see their data unintentionally leave the corporate network. The impact is proportional to the breadth of Copilot adoption within an organization.
What are the immediate security implications?
Unintended data exfiltration undermines confidentiality guarantees, can trigger regulatory violations, and provides threat actors with a foothold for further exploitation. If attackers gain visibility into the leaked files, they can craft spear‑phishing campaigns, credential‑stuffing attacks, or even ransomware payloads tailored to the disclosed content.
How can security teams detect this behavior?
Network detection systems should be tuned to flag outbound TLS connections to Microsoft’s AI service domains that carry unusually large payloads. Data‑loss‑prevention (DLP) solutions can inspect the content of Office‑365 traffic for unexpected file signatures. Additionally, audit logs in the Microsoft 365 compliance center can reveal Copilot‑related API calls that deviate from normal usage patterns.
What mitigation steps should organizations take right now?
First, review the Copilot deployment status in the Microsoft 365 admin portal and consider disabling the feature for high‑risk workloads until the data‑handling behavior is clarified. Second, enforce strict egress filtering to restrict traffic to known Microsoft AI endpoints and apply deep‑packet inspection where possible. Third, update DLP policies to include Copilot‑generated content and enforce encryption for files at rest and in transit.
How does GetKhojo help with attack‑surface awareness?
GetKhojo’s cloud‑asset scanner maps every external endpoint that a tenant contacts, surfacing hidden data‑exfiltration paths like the Copilot AI back‑end. By correlating network flows with asset inventories, security teams can quickly pinpoint over‑privileged services and remediate them before they become a breach vector. The platform also offers continuous monitoring dashboards that alert on anomalous outbound traffic patterns.
What longer‑term practices improve privacy hygiene?
Adopt a zero‑trust mindset: verify every request, enforce least‑privilege access, and segment AI services from core data repositories. Regularly audit third‑party integrations for data‑minimization guarantees, and maintain an up‑to‑date data‑classification framework so that sensitive documents trigger additional safeguards when processed by AI assistants.
What does this mean for you?
Organizations using Microsoft Copilot must treat it as a potential data‑exfiltration vector, not just a productivity booster. Conduct immediate scans with GetKhojo, tighten egress controls, and consider a phased rollout that includes explicit user consent for any content sent to AI services. By combining visibility, policy enforcement, and privacy‑first design, you can reap the benefits of AI while keeping your data locked down.
Frequently asked questions
Can I disable Microsoft Copilot for specific users without turning off the entire service?
Yes, Microsoft 365 admins can assign Copilot permissions at the user or group level, allowing you to keep the feature disabled for high‑risk accounts while retaining it for others.
What network indicators should I look for to spot Copilot‑related data leaks?
Watch for outbound TLS connections to Microsoft’s AI domains (e.g., *.openai.azure.com) that carry unusually large payloads or file signatures not typical of standard Office traffic.
Is there a way to audit which files Copilot has accessed in my tenant?
The Microsoft 365 compliance center logs Copilot API calls, and you can cross‑reference those logs with file‑access events to identify which documents were sent for processing.
How does GetKhojo differentiate between legitimate AI traffic and malicious exfiltration?
GetKhojo correlates known AI endpoint signatures with the size and frequency of data transfers, flagging anomalies that exceed baseline usage patterns for further investigation.
Will disabling Copilot affect other Microsoft 365 services?
Disabling Copilot only removes the AI assistance layer; core services like Exchange, SharePoint, and Teams continue to operate normally.
