Table of Contents
Why are my browser extensions failing on the Microsoft Entra login screen?
Microsoft has strengthened the authentication perimeter for Microsoft Entra ID. This update focuses on the prevention of Cross-Site Scripting (XSS) attacks. The primary mechanism involves a rigorous update to the Content Security Policy (CSP) at the login.microsoftonline.com endpoint. Administrators must understand that this change deliberately breaks functionality for any tool attempting to inject code during the login process.
The Technical Shift: Content Security Policy (CSP)
The core of this update lies in the Content Security Policy. A CSP acts as a gatekeeper for web browsers. It defines which dynamic resources are allowed to load. Microsoft has restricted this policy significantly.
- Old State: Less restrictive allowance for scripts interacting with the login page.
- New State: Strict “allowlist” enforcement. Only scripts originating from trusted Microsoft domains execute.
This architecture aligns with the broader Microsoft Secure Future Initiative. The goal is the elimination of vectors where attackers might inject malicious JavaScript to capture credentials or session tokens.
Impact on Enterprise Environments
This update creates immediate operational consequences for organizations relying on third-party browser extensions.
Blocked Functionality
Any browser extension or local tool that modifies the DOM (Document Object Model) of the Microsoft login page will fail. This includes:
- Password managers that use aggressive script injection.
- Custom branding tools that overlay the standard Microsoft prompt.
- Security tools that attempt to “scrape” the login page for monitoring purposes.
Administrator Action Items
IT leadership must audit the standard operating environment (SOE). If your organization deploys extensions to manage user sign-ins, test them immediately. If an extension injects code, it will no longer function. The authentication process itself remains unchanged for users who do not rely on these specific types of invasive tools.
Timeline and Deployment
While internal targets aimed for a mid-October 2025 rollout, official documentation surfaced in late November 2025. This discrepancy suggests a phased or rolling deployment. Regardless of the exact start date, the policy is now active. Administrators should assume strict CSP enforcement is in effect globally and adjust their support documentation to reflect that third-party modifications to the login screen are now prohibited by design.