Windows Shell Numeric Truncation Flaw (CVE-2025-49679): A Gateway to Privilege Escalation

Introduction

A numeric truncation vulnerability in Windows Shell, identified as CVE-2025-49679, presents a significant security risk by enabling authorized local attackers to escalate privileges to SYSTEM level. This flaw, rated 7.8 (High) on the CVSS scale, underscores critical weaknesses in numeric handling within legacy Windows components, potentially allowing attackers to bypass security controls and execute arbitrary code with elevated privileges.

Technical Information

CVE-2025-49679 is rooted in improper numeric type conversions within Windows Shell, specifically when casting 64-bit integers to 32-bit integers without adequate validation. This numeric truncation error (CWE-197) results in the loss of significant bits, causing unexpected and incorrect memory references. Attackers can exploit this vulnerability through several vectors, including shell extension hijacking, COM object manipulation, and desktop window manager abuse. By crafting malicious payloads that leverage truncated numeric values, attackers can manipulate memory addresses or function pointers, ultimately executing arbitrary code with elevated privileges.

The vulnerability affects critical Windows Shell components such as shell32.dll and explorer.exe, impacting taskbar operations, file associations, shell automation interfaces, and desktop rendering pipelines. Exploitation could lead to severe security breaches, including unauthorized system modifications, credential extraction, and persistent malware installation.

Patch Information

Microsoft has addressed the elevation of privilege vulnerability in Windows Shell (CVE-2025-49679) by releasing a security update on July 8, 2025. This update rectifies a numeric truncation error that could allow an authorized attacker to gain elevated privileges locally.

The patch is included in the cumulative update KB5062552, which applies to Windows 11 versions 22H2 and 23H2. By installing this update, the vulnerability is effectively mitigated, preventing potential exploitation.

To apply the update, users should navigate to Settings > Windows Update and check for updates. Alternatively, the update can be downloaded and installed manually from the Microsoft Update Catalog.

Affected Systems and Versions

The vulnerability specifically impacts Windows 11 versions 22H2 and 23H2. Users and administrators should ensure these versions are updated promptly to mitigate the risk.

Vendor Security History

Microsoft has historically demonstrated responsiveness in addressing vulnerabilities through its regular Patch Tuesday updates. However, numeric truncation and integer handling vulnerabilities have recurred in Windows Shell, indicating ongoing challenges in legacy codebases. Microsoft's consistent patching cadence remains a critical factor in mitigating these risks.

References

Security teams should prioritize patch deployment and remain vigilant for potential exploitation attempts.

Source: This report was created using AI

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