CVE-2026-41100: Microsoft 365 Copilot Auth Bypass Flaw

CVE-2026-41100 Overview

CVE-2026-41100 is an improper access control vulnerability [CWE-284] in Microsoft 365 Copilot. The flaw allows an authorized attacker with local access to perform spoofing actions against the application. Microsoft has documented the issue in its security update guide and confirmed the Android distribution of M365 Copilot is affected.

The vulnerability requires local access and low privileges, with no user interaction needed. Exploitation produces limited impact on confidentiality and integrity, with no impact on availability. No public exploit code, proof-of-concept, or in-the-wild exploitation has been reported.

Critical Impact

An authorized local attacker can spoof identity or interface elements within Microsoft 365 Copilot, potentially deceiving users into trusting attacker-controlled content surfaced through the assistant.

Affected Products

• Microsoft 365 Copilot (Android client)
• Vendor: Microsoft
• Component: microsoft:365_copilot

Discovery Timeline

• 2026-05-12 - CVE-2026-41100 published to the National Vulnerability Database
• 2026-05-12 - Microsoft publishes security update guide entry for CVE-2026-41100
• 2026-05-16 - Last updated in NVD database

Technical Details for CVE-2026-41100

Vulnerability Analysis

The vulnerability stems from improper access control [CWE-284] within Microsoft 365 Copilot on Android. Access control decisions inside the application do not adequately distinguish between trusted application content and content or actions that an authorized local actor can influence. As a result, an attacker who already holds valid credentials and local access to the device can perform spoofing operations against the Copilot experience.

Spoofing in this context means the attacker can present content, prompts, or responses in a way that appears to originate from a trusted source within Copilot. Because the CVSS vector indicates local attack vector with low privileges required and no user interaction, the threat model centers on a logged-in user device where another authorized principal abuses access boundaries between application surfaces.

The scope is unchanged, meaning the impact is confined to the vulnerable component. Confidentiality and integrity impacts are low, and there is no availability impact.

Root Cause

The root cause is insufficient enforcement of access control checks on operations that influence what Copilot presents to the user. The application trusts inputs or contexts that should require stronger validation, enabling an authorized attacker to inject or alter content that appears trustworthy. Microsoft has not publicly released technical details beyond the categorization under CWE-284.

Attack Vector

Exploitation requires local access to a device running Microsoft 365 Copilot on Android and a low-privilege authorized account. The attacker leverages the access control gap to spoof Copilot content or identity attributes. Successful exploitation does not require user interaction beyond ordinary Copilot use. Refer to the Microsoft Security Update Guide for CVE-2026-41100 for vendor-specific details.

Detection Methods for CVE-2026-41100

Indicators of Compromise

• No vendor-published indicators of compromise are available for CVE-2026-41100 at this time.
• Unexpected Copilot responses, prompts, or UI elements presented to end users that do not align with typical assistant output.
• Local application activity on Android devices that correlates with anomalous Copilot interactions from non-primary user accounts.

Detection Strategies

• Audit Microsoft 365 Copilot version inventory across managed Android devices using mobile device management (MDM) telemetry.
• Correlate Copilot usage logs in Microsoft Purview and Microsoft 365 audit logs for atypical query patterns or repeated identity context switches.
• Review Entra ID sign-in logs for the affected user accounts to identify local access from secondary principals coinciding with Copilot activity.

Monitoring Recommendations

• Enable and centralize Microsoft 365 audit logging for Copilot interactions.
• Monitor MDM compliance reports to confirm Android devices are running the patched Copilot build.
• Track Microsoft Security Response Center advisories for updates to CVE-2026-41100 detection guidance.

How to Mitigate CVE-2026-41100

Immediate Actions Required

• Update Microsoft 365 Copilot on Android to the latest version distributed through the Google Play Store as referenced in the Microsoft advisory.
• Enforce MDM policies that require current application versions on enrolled Android devices.
• Restrict local device access to authorized users only and disable shared-account usage on mobile endpoints.

Patch Information

Microsoft addresses CVE-2026-41100 through its standard security update channel for Microsoft 365 Copilot on Android. Consult the Microsoft Security Update Guide entry for CVE-2026-41100 for the fixed build identifier and rollout details.

Workarounds

• No vendor-supplied workarounds are listed; applying the updated Copilot release is the supported remediation path.
• Limit Copilot usage on shared or kiosk-style Android devices until patch deployment is verified.
• Educate users to validate sensitive Copilot responses through an authoritative secondary channel when uncertainty exists.