CVE-2025-49679 Overview
CVE-2025-49679 is a numeric truncation error [CWE-197] in the Microsoft Windows Shell component. An authenticated local attacker can exploit the flaw to elevate privileges on affected systems. Microsoft classifies the issue as high severity with a CVSS 3.1 base score of 7.8.
The vulnerability affects a broad range of supported Windows client and server releases, from Windows 10 1507 through Windows 11 24H2, and from Windows Server 2008 through Windows Server 2025. Successful exploitation results in high impact to confidentiality, integrity, and availability on the compromised host.
Critical Impact
Local privilege escalation from a standard user context to elevated privileges through numeric truncation in Windows Shell, enabling full control of the affected host.
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
- 2025-07-08 - CVE-2025-49679 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-49679
Vulnerability Analysis
CVE-2025-49679 is a numeric truncation error in Windows Shell. Numeric truncation occurs when a value stored in a larger integer type is converted to a smaller type without validating that the value fits. The truncated value then drives subsequent logic such as buffer sizing, index calculation, or access decisions.
When Windows Shell processes attacker-controlled input through the affected code path, the truncated integer produces a state the developer did not anticipate. This mismatched state can be leveraged to gain code execution or modify resources in the context of a higher-privileged process. Because Windows Shell runs interactive user sessions and integrates with numerous system components, an attacker who controls the truncation outcome can pivot from a standard user session to SYSTEM-level operations.
Root Cause
The root cause is improper handling of an integer conversion inside Windows Shell code, categorized as [CWE-197] Numeric Truncation Error. A value from a wider integer type is assigned or cast to a narrower type without a range check, silently discarding high-order bits and yielding a value that fails downstream security assumptions.
Attack Vector
The attack vector is local. An attacker must already have valid low-privileged credentials on the target host. From that context, the attacker triggers the vulnerable Shell code path, controls the truncated value, and elevates privileges without user interaction. Remote exploitation over the network is not applicable.
No public exploit is available at this time, no proof-of-concept has been published, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the Microsoft Security Update for CVE-2025-49679 for vendor technical detail.
Detection Methods for CVE-2025-49679
Indicators of Compromise
- Unexpected child processes spawned by explorer.exe or other Windows Shell components running at higher integrity levels than the parent user session.
- Creation of new local administrator accounts or modifications to privileged group membership shortly after Shell activity.
- Anomalous token manipulation events (Windows Security Event ID 4672, 4673) tied to non-administrative user sessions.
Detection Strategies
- Monitor for integrity-level escalations where a Medium-integrity Shell process spawns High or System integrity children without an approved UAC prompt path.
- Alert on suspicious loads of Shell extensions, COM objects, or DLLs from user-writable paths by explorer.exe or shell32.dll-hosted processes.
- Correlate local logon events with rapid privilege changes on the same host to surface elevation attempts consistent with local EoP chains.
Monitoring Recommendations
- Enable Sysmon with Process Create (Event ID 1), Image Load (Event ID 7), and Process Access (Event ID 10) logging on all workstations and servers.
- Forward Windows Security, Sysmon, and PowerShell logs to a centralized SIEM or data lake for behavioral correlation.
- Validate that endpoint identification tooling is enrolled and reporting on all in-scope Windows 10, Windows 11, and Windows Server hosts.
How to Mitigate CVE-2025-49679
Immediate Actions Required
- Apply the Microsoft security update for CVE-2025-49679 to all affected Windows client and server systems using the MSRC advisory.
- Prioritize patching on multi-user systems, terminal servers, and hosts where standard users log on interactively, since these expose the local attack surface most directly.
- Audit local accounts and remove unnecessary interactive logon rights to reduce the population of principals able to trigger the flaw.
Patch Information
Microsoft has released security updates through the standard Windows Update and WSUS channels. Consult the Microsoft Security Update for CVE-2025-49679 for the specific KB article and build numbers that apply to each affected Windows version. Confirm patch installation with wmic qfe list or the Get-HotFix PowerShell cmdlet.
Workarounds
- No official vendor workaround is documented. Patching is the supported remediation path.
- Restrict interactive and Remote Desktop logon rights via Group Policy so only required users can reach the local attack surface.
- Enforce least privilege and application control (Windows Defender Application Control, AppLocker) to limit what a low-privileged attacker can execute before triggering the Shell code path.
# Verify the security update is installed (PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Restrict interactive logon to a defined group via secedit
secedit /export /cfg C:\policy.inf
# Edit SeInteractiveLogonRight to include only required principals, then:
secedit /configure /db secedit.sdb /cfg C:\policy.inf
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
