Medium

FlagLeft spoofing vulnerability in Microsoft 365 Copilot for Android

IdentifiersCVE-2026-41100CWE-284· Improper Access Control

CVE-2026-41100 is a local spoofing vulnerability in Microsoft 365 Copilot for Android caused by improper access control in a shared Microsoft Android SDK. Reporting indicates a production debug setting, setIsDebugMode(true), was left enabled, which disabled the trust verification intended to restrict account-token sharing to trusted Microsoft applications only. As a result, a co-installed malicious Android application could request and obtain the signed-in user’s Microsoft account token from Microsoft 365 Copilot without a password prompt, login prompt, permission prompt, or other user interaction. Microsoft classified the issue as spoofing under CWE-284 and assigned CVSS 3.1 4.4 (AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N).

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows an authorized local attacker to spoof the user within Microsoft services by obtaining valid account tokens from Microsoft 365 Copilot for Android. With the stolen token, the attacker may gain access to some sensitive information and make limited changes as the victim user, including actions such as reading email, accessing files, viewing calendar data, or sending messages, depending on token scope. The issue has low confidentiality and integrity impact and no availability impact according to Microsoft. Use of the token may appear routine in logs, reducing visibility of abuse.

Mitigation

If you can’t patch tonight, do this now.

Until all devices are patched, reduce risk by preventing installation of untrusted Android applications on devices running Microsoft 365 Copilot, enforcing app allow-listing or managed Google Play policies through MDM, and monitoring OAuth/token activity for anomalous access patterns. Verify devices are no longer running vulnerable builds and consider revoking refresh tokens for accounts that may have been exposed, since application updates alone may not invalidate previously stolen tokens.

Remediation

Patch, then assume compromise.

Apply the official Microsoft security update for Microsoft 365 Copilot for Android delivered through Google Play. Ensure managed Android devices are updated to the latest fixed build available from Microsoft. Because reporting indicates exposed tokens may be long-lived refresh tokens, organizations should also assess whether potentially exposed refresh tokens need to be revoked after patching.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

Microsoft Corporation365 Copilotapplication

Microsoft Corporation365 Copilot Androidapplication

Microsoft CorporationExcelapplication

Microsoft CorporationLoopapplication

Microsoft CorporationM365 Copilotapplication

Microsoft CorporationOnenote For Androidapplication

Microsoft CorporationPowerpointapplication

Microsoft CorporationWordapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

4 SOURCESView more in app

the hacker newsNews

Jun 3, 2026

Microsoft 365 Android Apps Let Any App Steal Account Tokens via Leftover Debug Flag

A spoofing/improper access control vulnerability in Microsoft 365 Copilot for Android caused by a debug flag left enabled, allowing an untrusted app on the same device to obtain Microsoft account tokens intended only for trusted Microsoft apps.

cyber security newsNews

Jun 3, 2026

Microsoft 365 Android Apps Account Takeover Vulnerability Impacted Billions of Android Users

An improper access control issue associated with the FlagLeft vulnerability affecting Microsoft 365 Copilot for Android, enabling unauthorized token access via the shared SDK debug flag flaw.

msrc microsoftNews

May 12, 2026

CVE-2026-41100 - Security Update Guide - Microsoft - Microsoft 365 Copilot for Android Spoofing Vulnerability

A spoofing vulnerability in Microsoft 365 Copilot for Android caused by improper access control, allowing an authorized local attacker to perform spoofing with low confidentiality and integrity impact.

What this page doesn’t show

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Exposure mapping

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Threat actor evidence

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Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1