CVE-2026-24307: M365 Copilot Information Disclosure Flaw

CVE-2026-24307 Overview

CVE-2026-24307 is a critical input validation vulnerability in Microsoft 365 Copilot that allows unauthorized attackers to disclose sensitive information over a network. The vulnerability stems from improper validation of specified types of input (CWE-1287), which can be exploited remotely without requiring authentication, though user interaction is needed.

This vulnerability is particularly concerning as it affects M365 Copilot, Microsoft's AI-powered productivity assistant that processes vast amounts of organizational data. Successful exploitation could lead to unauthorized access to confidential information processed by Copilot, potentially exposing sensitive business documents, communications, and other protected data.

Critical Impact

Unauthorized attackers can exploit improper input validation in M365 Copilot to disclose sensitive organizational information over the network, with potential for high confidentiality and integrity impact.

Affected Products

• Microsoft 365 Copilot

Discovery Timeline

• January 22, 2026 - CVE-2026-24307 published to NVD
• January 22, 2026 - Last updated in NVD database

Technical Details for CVE-2026-24307

Vulnerability Analysis

This vulnerability falls under the Improper Input Validation category, specifically CWE-1287 (Improper Validation of Specified Type of Input). The flaw exists in how M365 Copilot processes and validates certain types of input data before using it in operations.

When Copilot receives specially crafted input that does not conform to expected data types or formats, the application fails to properly validate and sanitize this input. This inadequate validation can be leveraged by attackers to bypass security controls and extract information that should otherwise be protected.

The network-based attack vector means exploitation can occur remotely, though user interaction is required for the attack to succeed. The scope is changed, indicating that a successful exploit can affect resources beyond the vulnerable component's security scope. Both confidentiality and integrity are highly impacted, while availability remains unaffected.

Root Cause

The root cause of CVE-2026-24307 lies in insufficient type validation mechanisms within M365 Copilot's input processing pipeline. The application fails to properly verify that incoming data matches expected types before processing, allowing malformed or malicious input to be interpreted in unintended ways. This type confusion or improper type handling can lead to information disclosure when attackers craft inputs that exploit the validation gap.

Attack Vector

The attack is executed over the network and requires some form of user interaction to be successful. An attacker could potentially:

1. Craft malicious input designed to bypass Copilot's type validation checks
2. Deliver this input through a method that prompts user interaction (such as a specially crafted document or link)
3. Exploit the validation flaw to access or exfiltrate sensitive information processed by Copilot

The changed scope indicates that the vulnerability's impact extends beyond M365 Copilot itself, potentially affecting other Microsoft 365 services or data stores that Copilot has access to. This characteristic makes the vulnerability particularly dangerous in enterprise environments where Copilot may have broad access to organizational data.

Due to the nature of this AI-powered service, successful exploitation could potentially expose any data that Copilot has permission to access within the Microsoft 365 environment.

Detection Methods for CVE-2026-24307

Indicators of Compromise

• Unusual or unexpected queries being processed by M365 Copilot that contain malformed data types
• Anomalous data access patterns where Copilot retrieves information outside normal user workflows
• Authentication logs showing Copilot-related activity from unusual sources or at unexpected times

Detection Strategies

• Monitor Microsoft 365 audit logs for unusual Copilot activity patterns, particularly requests with malformed input structures
• Implement Data Loss Prevention (DLP) policies to detect unexpected data exfiltration through Copilot interfaces
• Review Copilot usage logs for requests that result in errors followed by successful data retrieval
• Analyze network traffic for anomalous patterns in Copilot-related API calls

Monitoring Recommendations

• Enable enhanced Microsoft 365 Defender monitoring for Copilot-related activities
• Configure alerts for bulk data access through Copilot that deviates from baseline user behavior
• Implement continuous monitoring of Copilot permission scopes and access patterns
• Review Microsoft Secure Score recommendations related to Copilot security configurations

How to Mitigate CVE-2026-24307

Immediate Actions Required

• Review and apply any available security updates from Microsoft for M365 Copilot
• Audit Copilot permissions and restrict access to sensitive data repositories where possible
• Educate users about potential social engineering vectors that may be used to trigger exploitation
• Enable advanced threat protection features in Microsoft 365 Defender

Patch Information

Microsoft has released a security advisory for this vulnerability. Organizations should monitor the Microsoft Security Response Center advisory for CVE-2026-24307 for official patch information and remediation guidance.

As a cloud service, M365 Copilot security updates are typically applied by Microsoft automatically. However, administrators should verify their tenant is receiving updates and review any configuration changes recommended by Microsoft.

Workarounds

• Limit Copilot's access to sensitive data repositories through Microsoft 365 access policies until patches are confirmed applied
• Implement strict conditional access policies for Copilot usage, particularly from external networks
• Consider temporarily disabling Copilot features for users handling highly sensitive data if risk assessment warrants
• Apply principle of least privilege to all data sources accessible by Copilot

# Example: PowerShell to review Copilot access policies in your tenant
# Connect to Microsoft 365
Connect-MgGraph -Scopes "Policy.Read.All"

# Review conditional access policies affecting Copilot
Get-MgIdentityConditionalAccessPolicy | Where-Object {$_.DisplayName -like "*Copilot*"}

# Review Copilot app permissions
Get-MgServicePrincipal -Filter "displayName eq 'Microsoft 365 Copilot'" | Select-Object DisplayName, AppId