CVE-2025-27737: Windows 10 1507 Auth Bypass Vulnerability

CVE-2025-27737 Overview

CVE-2025-27737 is a security feature bypass vulnerability affecting Windows Security Zone Mapping caused by improper input validation. This vulnerability allows an unauthorized attacker to bypass critical security features locally, potentially undermining the trust boundaries established by Windows security zones. The flaw affects a broad range of Windows client and server operating systems, making it a significant concern for enterprise environments.

Windows Security Zone Mapping is a fundamental component that determines the trust level assigned to content based on its origin. By exploiting improper input validation in this component, attackers can cause Windows to misclassify content, effectively bypassing security restrictions that would normally apply to untrusted sources.

Critical Impact

Successful exploitation allows attackers to bypass Windows security zone restrictions, potentially enabling execution of malicious content with elevated trust levels that would normally be blocked or require user confirmation.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016, 2019, 2022, 2022 23H2, and 2025

Discovery Timeline

• April 8, 2025 - CVE-2025-27737 published to NVD
• July 10, 2025 - Last updated in NVD database

Technical Details for CVE-2025-27737

Vulnerability Analysis

The vulnerability resides in the Windows Security Zone Mapping component, which is responsible for categorizing content into security zones (Local Machine, Local Intranet, Trusted Sites, Internet, and Restricted Sites). Each zone has different security policies that control how Windows handles content from that zone.

The improper input validation flaw (CWE-20) allows attackers to craft malicious input that manipulates how Windows categorizes content. When exploited successfully, content that should be treated as originating from an untrusted zone (such as the Internet zone) may instead be processed as if it came from a trusted zone, bypassing critical security checks and prompts.

This type of vulnerability is particularly dangerous because security zones are a foundational security mechanism in Windows, affecting how browsers, Office applications, and other Windows components handle downloaded content and Mark of the Web (MotW) protections.

Root Cause

The root cause is improper input validation in the Windows Security Zone Mapping implementation. The affected component fails to properly sanitize or validate input that determines security zone classification, allowing specially crafted input to manipulate the zone assignment logic. This validation failure enables attackers to exploit edge cases in the zone mapping algorithm to achieve incorrect zone categorization.

Attack Vector

The attack requires local access to the target system and user interaction. An attacker would typically need to convince a user to interact with a malicious file or content. The attack flow involves:

1. The attacker crafts content with specially manipulated zone indicators or properties
2. The victim is enticed to open or interact with the malicious content
3. Windows Security Zone Mapping incorrectly categorizes the content due to the validation flaw
4. Security protections that would normally apply are bypassed, allowing the malicious content to execute with elevated trust

The vulnerability has scope change implications, meaning successful exploitation can affect resources beyond the vulnerable component's security scope. This amplifies the potential impact, as bypassing zone restrictions can lead to compromise of confidentiality, integrity, and availability of the system.

Detection Methods for CVE-2025-27737

Indicators of Compromise

• Unusual files with mismatched zone identifiers in Alternate Data Streams (ADS)
• Evidence of content executing without expected security prompts or Mark of the Web warnings
• Windows Security event logs showing unexpected security zone assignments for downloaded content
• Files originating from the Internet executing with Local Intranet or Trusted Sites permissions

Detection Strategies

• Monitor Windows Security events for anomalies in zone assignment for downloaded content
• Deploy endpoint detection rules to identify files with manipulated zone identifier metadata
• Implement file integrity monitoring to detect unauthorized modifications to zone configuration data
• Use SentinelOne Singularity Platform to detect exploitation attempts through behavioral analysis

Monitoring Recommendations

• Enable verbose logging for Windows Security Zone operations where possible
• Monitor for processes spawned from content that bypassed expected security prompts
• Track Alternate Data Stream modifications on downloaded files
• Implement centralized logging for security zone-related events across the enterprise

How to Mitigate CVE-2025-27737

Immediate Actions Required

• Apply Microsoft's security patches immediately from the April 2025 Patch Tuesday release
• Prioritize patching for systems that regularly interact with external content or untrusted sources
• Review and restrict user permissions to minimize the impact of potential exploitation
• Ensure SentinelOne agents are updated to detect post-exploitation behaviors

Patch Information

Microsoft has released security updates to address this vulnerability as part of their regular update cycle. Administrators should obtain the appropriate patches from the Microsoft Security Update Guide for CVE-2025-27737. The patches address the improper input validation issue in the Windows Security Zone Mapping component.

Organizations should use Windows Server Update Services (WSUS), Microsoft Endpoint Configuration Manager, or Windows Update for Business to deploy patches across their environments. Given the broad range of affected Windows versions, ensure patch deployment covers all operating system variants in your infrastructure.

Workarounds

• Restrict execution of content from untrusted sources through Group Policy
• Configure Windows Defender SmartScreen to block unrecognized applications
• Implement application whitelisting to prevent execution of unauthorized content regardless of zone classification
• Enable Protected View for Office documents and strengthen macro security settings
• Use network segmentation to limit lateral movement if a system is compromised

# PowerShell: Review current Internet Zone security settings
Get-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3" | Select-Object *

# Verify Mark of the Web is being applied to downloaded files
Get-Item "C:\path\to\downloaded\file.exe" -Stream Zone.Identifier -ErrorAction SilentlyContinue