CVE-2025-59214: Windows 10 1507 Information Disclosure

CVE-2025-59214 Overview

CVE-2025-59214 is an information disclosure vulnerability in Windows File Explorer that allows an unauthorized attacker to perform spoofing over a network. The flaw, categorized under [CWE-200], exposes sensitive information to an unauthorized actor when a user interacts with attacker-controlled content. Public technical analysis by Cymulate links the issue to NTLM credential leakage triggered through File Explorer. The vulnerability affects all currently supported Windows client and Windows Server releases.

Critical Impact

Successful exploitation enables network-based attackers to capture NTLM authentication material from victim systems, supporting relay attacks, offline cracking, and account spoofing across enterprise environments.

Affected Products

• Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2)
• Microsoft Windows 11 (22H2, 23H2, 24H2, 25H2)
• Microsoft Windows Server 2008, 2012, 2016, 2019, 2022 (including 23H2), and 2025

Discovery Timeline

• 2025-10-14 - CVE-2025-59214 published to NVD
• 2026-03-27 - Last updated in NVD database

Technical Details for CVE-2025-59214

Vulnerability Analysis

The vulnerability resides in Windows File Explorer's handling of file metadata and embedded references rendered when displaying directories or previewing files. When File Explorer processes a crafted artifact, it initiates an outbound network connection to an attacker-controlled host. That connection carries Windows authentication material, exposing NTLM hashes belonging to the logged-on user.

The flaw maps to [CWE-200], Exposure of Sensitive Information to an Unauthorized Actor. According to the public Cymulate analysis, the leak surfaces during routine Explorer rendering, which means the user does not need to open the malicious file directly. Network-based exploitation succeeds at low complexity but requires user interaction such as browsing a shared folder.

Root Cause

File Explorer dereferences external paths embedded in file metadata without enforcing checks that would prevent authenticated SMB or WebDAV requests to untrusted hosts. The operating system then attaches the current user's NTLM credentials to the outbound handshake, satisfying the remote server's authentication challenge. The Cymulate writeup documents how an attacker observes the resulting Net-NTLMv2 response on a listener under their control.

Attack Vector

An attacker stages a crafted file, shortcut, or shared resource referencing an external UNC path pointing to their server. The victim navigates to a folder containing the artifact using Windows File Explorer. Explorer parses the metadata, issues authenticated requests to the remote host, and discloses NTLM material. The captured hash supports NTLM relay against services lacking SMB signing or offline brute-force recovery of the plaintext password.

The vulnerability is described in prose only because no sanitized exploit code from the original reporter is available. Refer to the Cymulate Blog on NTLM Leak for technical reproduction details.

Detection Methods for CVE-2025-59214

Indicators of Compromise

• Outbound SMB (TCP/445) or WebDAV (TCP/80, TCP/443) connections from end-user workstations to untrusted external or unexpected internal hosts
• explorer.exe initiating network authentication to hosts outside the corporate authentication boundary
• Unexpected Net-NTLMv2 authentication attempts logged at perimeter listeners or honeypots
• Files with suspicious icon, thumbnail, or shortcut references pointing to attacker-controlled UNC paths

Detection Strategies

• Inspect process telemetry for explorer.exe spawning network connections to non-domain SMB or WebDAV destinations
• Correlate Windows Security Event ID 4624/4625 logon attempts with file browsing activity on user endpoints
• Hunt for Office documents, .lnk, .url, .library-ms, and .search-ms files containing external UNC references received via email or downloaded from the internet
• Deploy canary SMB listeners on internal segments to detect coerced NTLM authentication

Monitoring Recommendations

• Alert on any SMB egress traffic leaving the corporate network perimeter, which should be blocked by policy
• Monitor changes to NTLM auditing policies and review the resulting NTLM operational logs
• Track downloads of file types known to carry external references, especially from email and web vectors
• Review the Vicarius Detection Script for CVE-2025-59214 for endpoint-side checks

How to Mitigate CVE-2025-59214

Immediate Actions Required

• Apply the October 2025 Microsoft security updates referenced in the Microsoft CVE-2025-59214 advisory to all affected Windows clients and servers
• Block outbound TCP/445 and outbound WebDAV traffic at the perimeter firewall
• Enforce SMB signing and Extended Protection for Authentication on all SMB and HTTP services to defeat NTLM relay
• Quarantine untrusted files received from email or external file shares pending inspection

Patch Information

Microsoft addressed CVE-2025-59214 in the October 2025 Patch Tuesday release. Administrators should consult the Microsoft Security Response Center advisory for the specific KB articles corresponding to each affected Windows build. The Vicarius Mitigation Script for CVE-2025-59214 provides supplementary remediation automation.

Workarounds

• Restrict outgoing NTLM traffic using the Network security: Restrict NTLM: Outgoing NTLM traffic to remote servers group policy set to Deny all
• Disable the WebClient service on endpoints that do not require WebDAV connectivity to prevent HTTP-based credential coercion
• Configure host-based firewall rules to block SMB egress from user workstations
• Educate users to avoid browsing untrusted file shares and to report unexpected file deliveries

# Configuration example: restrict outgoing NTLM and disable WebClient via PowerShell
Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0' -Name 'RestrictSendingNTLMTraffic' -Value 2 -Type DWord
Set-Service -Name WebClient -StartupType Disabled
Stop-Service -Name WebClient -Force
New-NetFirewallRule -DisplayName 'Block Outbound SMB' -Direction Outbound -Protocol TCP -RemotePort 445 -Action Block