CVE-2025-29839: Windows 10 Information Disclosure Flaw

CVE-2025-29839 Overview

CVE-2025-29839 is an out-of-bounds read vulnerability (CWE-125) affecting the Windows File Server component across a wide range of Microsoft Windows operating systems. This vulnerability allows an unauthorized attacker with local access to disclose potentially sensitive information from system memory. The out-of-bounds read condition occurs when the Windows File Server improperly handles memory boundaries, enabling data leakage that could expose system information to unauthorized parties.

Critical Impact

Local attackers can exploit this vulnerability to read memory beyond intended boundaries in Windows File Server, potentially exposing sensitive system information without requiring authentication.

Affected Products

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

Discovery Timeline

• May 13, 2025 - CVE-2025-29839 published to NVD
• May 19, 2025 - Last updated in NVD database

Technical Details for CVE-2025-29839

Vulnerability Analysis

This vulnerability represents an out-of-bounds read condition within the Windows File Server component. Out-of-bounds read vulnerabilities occur when software reads data past the end, or before the beginning, of the intended buffer. In this case, the Windows File Server fails to properly validate buffer boundaries before performing read operations, allowing an attacker to access memory contents beyond the allocated buffer space.

The attack requires local access to the target system, meaning the attacker must already have some form of presence on the machine. No user interaction is required for exploitation, and the attacker does not need elevated privileges or authentication to trigger the vulnerability. The impact is limited to confidentiality—no integrity or availability impact has been identified—making this primarily an information disclosure vulnerability.

Root Cause

The root cause of CVE-2025-29839 lies in improper input validation within the Windows File Server component. When processing certain operations, the component fails to adequately verify that read operations remain within the bounds of allocated memory buffers. This missing boundary check allows memory contents adjacent to legitimate buffers to be read and potentially disclosed to an attacker.

This type of vulnerability (CWE-125: Out-of-bounds Read) typically occurs when:

• Array indices are not properly validated against buffer sizes
• Length calculations are incorrect or missing
• Pointer arithmetic bypasses boundary checks

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to have existing access to the target system. An unauthorized attacker can exploit this vulnerability without authentication by crafting specific requests or inputs to the Windows File Server component that trigger the out-of-bounds read condition.

The exploitation scenario involves:

1. The attacker gains local access to a Windows system running an affected version
2. The attacker interacts with the Windows File Server component through legitimate interfaces
3. By providing specially crafted input, the attacker triggers the out-of-bounds read
4. Memory contents beyond the intended buffer boundaries are disclosed to the attacker

The disclosed information could potentially include sensitive data such as memory addresses, configuration information, or other data that could be leveraged for further attacks on the system. For detailed technical information, refer to the Microsoft Security Advisory.

Detection Methods for CVE-2025-29839

Indicators of Compromise

• Unusual read access patterns to Windows File Server components or related system files
• Unexpected memory access errors or exceptions in Windows File Server event logs
• Process behavior anomalies in services associated with file server operations
• Suspicious local user activity attempting to interact with file server components

Detection Strategies

• Monitor Windows Event Logs for abnormal Windows File Server component activity
• Deploy endpoint detection and response (EDR) solutions to detect memory access violations
• Enable advanced audit logging for file server operations to track unusual access patterns
• Utilize SentinelOne's behavioral analysis to detect exploitation attempts targeting memory vulnerabilities

Monitoring Recommendations

• Configure Security Information and Event Management (SIEM) rules to alert on Windows File Server anomalies
• Enable Windows Defender Exploit Guard with memory protection features
• Implement file integrity monitoring on critical Windows File Server binaries
• Review system logs regularly for indicators of local exploitation attempts

How to Mitigate CVE-2025-29839

Immediate Actions Required

• Apply the latest Microsoft security updates addressing CVE-2025-29839 immediately
• Audit systems to identify all affected Windows versions in your environment
• Restrict local access to systems running Windows File Server where possible
• Enable enhanced logging on affected systems to detect potential exploitation attempts
• Review and limit user permissions on file server systems to reduce attack surface

Patch Information

Microsoft has released security patches addressing CVE-2025-29839 as part of their security update process. Organizations should consult the Microsoft Security Response Center advisory for specific patch details and download the appropriate updates for their affected Windows versions. The patches address the out-of-bounds read condition by implementing proper boundary validation in the Windows File Server component.

Workarounds

• Limit local access to affected systems to only essential personnel and services
• Implement application allowlisting to prevent unauthorized binaries from executing
• Enable Windows Defender Credential Guard and other memory protection features
• Segment file server systems from general-purpose workstations to reduce exposure
• Monitor for and respond to any suspicious local activity on affected systems

# Verify Windows Update status and installed patches
# Run in elevated PowerShell
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20

# Check Windows File Server service status
Get-Service -Name LanmanServer | Select-Object Name, Status, StartType

# Enable advanced audit logging for file server
auditpol /set /subcategory:"Detailed File Share" /success:enable /failure:enable