Microsoft Fortifies Entra ID Logins: Blocking Unauthorized Scripts by 2026

Microsoft is set to significantly bolster the security of its Entra ID authentication system by blocking unauthorized script injections during user logins. This proactive measure, part of the company's Secure Future Initiative, aims to prevent malicious code from executing on login pages, thereby safeguarding user credentials and system integrity.

Key Takeaways

• Microsoft will enforce a stricter Content Security Policy (CSP) on Entra ID sign-in pages starting mid-to-late October 2026.

• Only scripts from trusted Microsoft domains will be permitted to run during authentication.

• This change is designed to protect against cross-site scripting (XSS) and other injection attacks.

• The policy applies to browser-based sign-ins at login.microsoftonline.com and will not affect Entra External ID.

• Organizations are advised to test their sign-in flows and discontinue the use of code-injecting browser extensions or tools.

Enhanced Security Through Content Security Policy

Starting in mid-to-late October 2026, Microsoft will implement a strengthened Content Security Policy (CSP) for Entra ID sign-in experiences. This update will ensure that only scripts originating from trusted Microsoft domains and content delivery networks (CDNs) are allowed to execute. Inline scripts will also be restricted to Microsoft-trusted sources. This move is intended to block any unauthorized or injected code that could be used in cross-site scripting (XSS) attacks, a common method for attackers to steal credentials or compromise systems.

Scope and Impact

The new policy will specifically target browser-based sign-in experiences for URLs beginning with . Microsoft Entra External ID and non-browser-based authentication methods will not be affected by this change. While most users and organizations will experience a seamless transition, those relying on browser extensions or third-party tools that inject scripts into the Entra ID sign-in page will need to adapt. These tools will cease to function once the policy is enforced, though users will still be able to log in.

Preparing for the Change

Microsoft is urging organizations to proactively test their sign-in flows ahead of the October 2026 deadline. Administrators can identify potential issues by opening their browser's developer console during a sign-in attempt. Any violations of the new CSP will be flagged in red text, providing details about the blocked scripts. Microsoft also recommends discontinuing the use of any browser extensions or tools that inject code into the sign-in process and switching to alternative solutions that do not modify the authentication flow. This proactive approach will help ensure a smooth transition and maintain a secure sign-in experience.

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Sources

• Microsoft to Block Unauthorized Scripts in Entra ID Logins with 2026 CSP Update, The Hacker News.

• Microsoft Blocks External Scripts in Entra ID Logins to Boost Security, GBHackers News.

• Microsoft to Block External Scripts in Entra ID Logins to Enhance Protections, CyberSecurityNews.

• Microsoft to Enhance Protections by Blocking External Scripts in Entra ID Logins, Cyber Press.

• Microsoft to secure Entra ID sign-ins from script injection attacks, BleepingComputer.