Security Advisory

Microsoft Teams Access Token Vulnerability Allows Attack Vector for Data Exfiltration

Summary: Microsoft Teams Access Token Vulnerability: New Attack Vector for Data Exfiltration

A recently uncovered vulnerability in Microsoft Teams for Windows allows attackers with local access to extract encrypted authentication tokens, granting unauthorized access to chats, emails and SharePoint files.

This technique, detailed by researcher Brahim El Fikhi on October 23, 2025, leverages the Windows Data Protection API (DPAPI) to decrypt tokens stored in a Chromium-like Cookies database.

Attackers can use these tokens for impersonation, lateral movement, or social engineering, bypassing recent security enhancements and posing significant risks to enterprise environments.

Vulnerability Details

The vulnerability, identified in Microsoft Teams desktop applications, involves the extraction of encrypted access tokens stored in the SQLite Cookies database at %AppData%\Local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams\EBWebView\Cookies. Unlike earlier versions that stored tokens in plaintext (a flaw exposed by Vectra AI in 2022), current versions use AES-256-GCM encryption protected by DPAPI, tied to user or machine credentials. However, attackers with local access can decrypt these tokens using tools like ProcMon and Mimikatz, exploiting the embedded msedgewebview2.exe process that handles authentication via login.microsoftonline.com.

Source: blog.randorisec.fr, cybersecuritynews
Attack Flow

StepDescription
CraftAttackers use ProcMon to monitor msedgewebview2.exe and identify the Cookies database write operations.
AccessThe ms-teams.exe process is terminated to unlock the Cookies file, which is locked during operation.
ExtractThe encrypted token is retrieved from the Cookies database, with fields like host_key (e.g., teams.microsoft.com), name, and encrypted_value (prefixed with “v10”).
DecryptThe DPAPI-protected master key is extracted from %AppData%\Local\Packages\MSTeams_8wekyb3d8bbwe\LocalCache\Microsoft\MSTeams\EBWebView\Local State and decrypted using Windows APIs or tools like Mimikatz.
ExploitDecrypted tokens are used with tools like GraphSpy to access Teams chats, send messages, read emails, or interact with SharePoint via Microsoft Graph API

Why It’s Effective

  • Local Access Exploitation: The attack requires only local access, achievable via malware or compromised endpoints, bypassing MFA and remote defenses.
  • Stealthy Execution: The use of standard Windows APIs (DPAPI) and embedded browser processes evades traditional monitoring.
  • Authority Abuse: Tokens enable impersonation through trusted APIs, amplifying risks of phishing or data theft via Teams, Outlook, or SharePoint.

Recommendations:

  • Monitor Processes – Deploy EDR rules to detect abnormal ms-teams.exe terminations or msedgewebview2.exe file writes.
  • Enforce Encryption – Use app-bound encryption and prefer web-based Teams to avoid local token storage.
  • Token Rotation – Implement Entra ID policies to rotate access tokens regularly and audit Graph API logs for anomalies.
  • Limit Privileges – Restrict local admin access to prevent DPAPI key extraction.
  • User Awareness – Train users to recognize phishing attempts via Teams or email, especially those leveraging impersonation

Conclusion:
This vulnerability underscores the evolving threat landscape for collaboration platforms like Microsoft Teams. As attackers refine techniques to exploit trusted systems, organizations must enhance endpoint monitoring and adopt stricter access controls. By implementing the outlined mitigations, security teams can reduce the risk of token-based attacks and safeguard sensitive data.

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