CVE-2025-54917: Windows 10 1507 Auth Bypass Vulnerability

CVE-2025-54917 Overview

CVE-2025-54917 is a security feature bypass vulnerability in the Windows MapUrlToZone function. The flaw allows an unauthorized attacker to circumvent zone-based protection mechanisms over a network. Exploitation requires user interaction, typically through opening a crafted URL or document that leverages the misclassified zone assignment. Microsoft rates the issue as medium severity with a CVSS v3.1 score of 4.3. The vulnerability affects supported versions of Windows client and Windows Server, including Windows 10, Windows 11, and Windows Server 2008 through 2025. The weakness is categorized under [CWE-693] Protection Mechanism Failure.

Critical Impact
Attackers can trick MapUrlToZone into placing untrusted content into a more privileged security zone, bypassing Mark-of-the-Web and Internet Zone protections that gate script execution and file handling warnings.

Affected Products

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

Discovery Timeline

2025-09-09 - CVE-2025-54917 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-54917

Vulnerability Analysis

The MapUrlToZone function is a Windows URL security API used by Internet Explorer components, Microsoft Office, and other applications to determine which security zone a URL belongs to. Zones such as Internet, Local Intranet, Trusted Sites, and Local Machine each carry different execution and content-handling policies. When MapUrlToZone returns an incorrect zone, downstream callers apply weaker restrictions than intended.

In CVE-2025-54917, a crafted URL is parsed in a way that causes the function to return a lower-risk zone than the content actually warrants. This allows content originating from an untrusted network location to inherit privileges associated with a trusted zone, bypassing warnings, prompts, or blocks that Windows would otherwise enforce.

Exploitation requires the victim to interact with attacker-supplied content, such as clicking a link or opening a document. The confidentiality impact is limited to low, with no direct impact on integrity or availability.

Root Cause

The root cause is a protection mechanism failure [CWE-693] in the URL parsing logic used by MapUrlToZone. Specifically, malformed or ambiguous URL constructions are not normalized consistently before zone lookup. This inconsistency between the parser used for zone mapping and the parser used for actual resource retrieval enables a mismatch attackers can exploit.

Attack Vector

The attack vector is network-based. An attacker hosts crafted content on an attacker-controlled server or embeds a malicious URL in email, chat, or a document. When the victim opens the resource, the affected Windows component calls MapUrlToZone on the URL, receives an incorrect zone classification, and processes the content with reduced restrictions. This can support downstream techniques such as bypassing Mark-of-the-Web, enabling silent execution of scripted content, or suppressing SmartScreen and Protected View prompts.

No public proof-of-concept exploit is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2025-54917

Indicators of Compromise

Unexpected outbound HTTP or HTTPS requests from Office applications, explorer.exe, or Internet Explorer engine hosts (ieframe.dll consumers) to unfamiliar domains.
Documents or shortcut files (.url, .lnk, .hta) referencing URLs with unusual encodings, embedded credentials, or path traversal artifacts.
Script execution or child process creation from Office and browser hosts without the expected Mark-of-the-Web warning events.

Detection Strategies

Hunt for process trees where winword.exe, excel.exe, outlook.exe, or browser processes spawn powershell.exe, cmd.exe, mshta.exe, or wscript.exe shortly after a URL open event.
Monitor Windows event logs for zone elevation prompts that were expected but did not fire, correlating with recent inbound URL clicks.
Inspect NTFS Zone.Identifier alternate data streams on downloaded files to confirm Mark-of-the-Web is applied consistently.

Monitoring Recommendations

Enable Attack Surface Reduction rules that block Office child processes and executable content from email or web origins.
Forward Sysmon Event IDs 1 (process create), 11 (file create), and 15 (file stream create) to a central SIEM for correlation.
Alert on any process referencing urlmon.dll or MapUrlToZone behavior anomalies where a network URL resolves to a Local Intranet or Trusted zone unexpectedly.

How to Mitigate CVE-2025-54917

Immediate Actions Required

Apply the September 2025 Microsoft security update referenced in the Microsoft Security Update CVE-2025-54917 advisory to all affected Windows client and server systems.
Prioritize patching internet-facing and user-interactive systems, including workstations, RDS hosts, and jump servers.
Verify patch deployment through configuration management tooling and confirm the updated urlmon.dll version is present.

Patch Information

Microsoft has released cumulative security updates for all affected Windows versions. Refer to the Microsoft Security Update CVE-2025-54917 advisory for the specific KB article and build numbers that correspond to each supported Windows release.

Workarounds

Restrict outbound network access from user workstations to reduce the reachability of attacker-controlled URLs.
Configure Internet Explorer and Edge (IE Mode) security zone policies via Group Policy to disable active scripting and file downloads in the Internet zone.
Enforce Protected View and block macros originating from the internet in Microsoft Office through administrative templates until patches are applied.

bash

# Configuration example: enforce ASR rules via PowerShell to reduce exposure
Set-MpPreference -AttackSurfaceReductionRules_Ids `
  D4F940AB-401B-4EFC-AADC-AD5F3C50688A `
  -AttackSurfaceReductionRules_Actions Enabled

# Verify Windows Update status for the CVE-2025-54917 patch
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10