Description

Incorrect permission assignment for critical resource in M365 Copilot allows an authorized attacker to disclose information over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.7",
  "pubDate": "2026-09-18T00:17:47.920Z",
  "pubdate": "2026-09-18T00:17:47.920Z",
  "executiveSummary": "A vulnerability involving incorrect permission assignment for critical resources has been identified within M365 Copilot, leading to potential unauthorized information disclosure.\nThis flaw resides within the access control mechanisms governing how M365 Copilot processes and retrieves data across the Microsoft 365 ecosystem.\nThe vulnerability allows an authorized user—an attacker already authenticated within the tenant—to leverage Copilot's integration to access data that should be restricted based on the user's defined permission set.\nThe primary impact is the unauthorized disclosure of sensitive organizational information, as the system fails to correctly enforce the Principle of Least Privilege when interacting with specific back-end resources.\nThe risk implication is significant, as it enables lateral movement of data exposure without requiring complex exploitation techniques, relying instead on the inherent trust established between the Copilot interface and the underlying data repositories.\nExploitation requires the attacker to hold legitimate access to the M365 environment, after which they can manipulate queries or service interactions to bypass resource-level authorization checks.\nThe vulnerability highlights a critical failure in the synchronization or evaluation of Access Control Lists (ACLs) when the service acts as an intermediary between the authenticated user and sensitive corporate data silos.",
  "technicalDetails": "The root cause of this vulnerability is an improper access control configuration within the M365 Copilot framework, which fails to consistently validate user-level permissions when fetching data from protected M365 resources. In a secure architecture, the service should enforce granular authorization checks at the data provider level, ensuring that the service identity or the proxied user identity does not exceed established access boundaries.\nThe attack flow begins with an authenticated attacker interacting with the M365 Copilot interface. Because the system incorrectly assigns or fails to verify permissions for specific critical resources, the Copilot engine assumes authorized context when fulfilling requests that the user would not normally be permitted to access through direct interface interactions.\nSpecifically, the vulnerability exists at the intersection of the Copilot processing engine and the underlying Graph API or data-retrieval layer. When a user provides a prompt or query, the service retrieves information from various M365 sources. If the configuration governing these resources does not properly propagate or enforce the user's specific access token limitations, the system may erroneously return restricted data to the requester.\nThe exploitation method involves the attacker crafting targeted queries designed to trigger the retrieval of data from resources where the authorization logic is flawed. By submitting these prompts through the M365 Copilot interface, the attacker forces the service to act as an agent that fetches data without re-validating the user's original permissions against the destination resource's ACLs.\nSince the service operates under an elevated system or service-to-service identity to maximize utility, the failure to verify the initiating user's permissions results in an unauthorized information disclosure over the network. The information is then presented directly within the Copilot response interface, effectively bypassing standard data loss prevention (DLP) controls that might otherwise flag direct access to these files or data objects.\nPost-exploitation impact involves the exfiltration of sensitive, non-public data, including potentially proprietary documents, internal communications, or sensitive metadata that the attacker should not have visibility into based on the organization's current identity and access management (IAM) policies. This bypasses the intended security perimeter, allowing for unauthorized data aggregation and potential reconnaissance within the enterprise environment."
}