CVE-2025-27739: Windows 10 1809 Privilege Escalation Flaw

CVE-2025-27739 Overview

CVE-2025-27739 is a local privilege escalation vulnerability in the Windows Kernel caused by an untrusted pointer dereference [CWE-822]. An authorized attacker with local access and low privileges can exploit this flaw to elevate to SYSTEM-level privileges. Microsoft published the advisory on April 8, 2025, as part of its coordinated Patch Tuesday release. The vulnerability affects a wide range of supported Windows client and server platforms, from Windows 10 1809 through Windows 11 24H2 and Windows Server 2019 through Windows Server 2025.

Critical Impact
Successful exploitation grants full control over the host by promoting a low-privileged local process to kernel or SYSTEM context, enabling credential theft, persistence, and defense evasion.

Affected Products

Microsoft Windows 10 (1809, 21H2, 22H2)
Microsoft Windows 11 (22H2, 23H2, 24H2)
Microsoft Windows Server 2019, 2022, 2022 23H2, and 2025

Discovery Timeline

2025-04-08 - Microsoft releases security update for CVE-2025-27739
2025-04-08 - CVE-2025-27739 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-27739

Vulnerability Analysis

The vulnerability resides in the Windows Kernel and is classified as an untrusted pointer dereference weakness [CWE-822]. The kernel dereferences a pointer value that originates from, or can be influenced by, an unprivileged user-mode caller. Because the pointer is not validated before dereference, an attacker can steer kernel execution to a memory location under their control.

Exploitation requires the attacker to already hold a local, authenticated foothold on the target machine. From that context, an attacker can craft input to a kernel interface (for example, an IOCTL or system call) that supplies the untrusted pointer. Successful exploitation results in code execution or arbitrary read/write in kernel context, breaking the boundary between user mode and Ring 0.

The flaw is a common privilege-escalation building block in post-compromise activity. Adversaries chain it with initial-access techniques such as phishing or commodity malware to reach SYSTEM and disable endpoint security, tamper with drivers, or extract LSASS secrets.

Root Cause

The root cause is missing or insufficient validation of a pointer supplied to, or derived from, a user-controllable input inside a kernel routine. When the kernel dereferences that pointer, it operates on attacker-chosen memory. This class of bug (CWE-822) frequently leads to arbitrary kernel read/write primitives that attackers convert into full elevation of privilege.

Attack Vector

The attack vector is local. An attacker must first authenticate to the target system with low privileges, then invoke the vulnerable kernel path to trigger the dereference. No user interaction is required beyond the attacker's own actions. Microsoft has not published exploit code, and CVE-2025-27739 is not currently listed on the CISA Known Exploited Vulnerabilities catalog.

No verified proof-of-concept code is publicly available. See the Microsoft Security Update Guide for CVE-2025-27739 for authoritative technical details.

Detection Methods for CVE-2025-27739

Indicators of Compromise

Unexpected creation of SYSTEM-context processes descending from low-privileged user sessions.
Kernel bug checks (BSOD) referencing invalid pointer dereferences shortly after suspicious process activity.
Loading of unsigned or newly written drivers immediately following a local logon by a standard user.
LSASS access or credential dumping activity from processes that recently transitioned to SYSTEM.

Detection Strategies

Hunt for privilege token elevation events where a non-administrative process suddenly runs with NT AUTHORITY\SYSTEM integrity.
Correlate Windows Event ID 4672 (special privileges assigned) with parent processes that were previously running as standard users.
Monitor for anomalous use of NtQuerySystemInformation, NtMapViewOfSection, or driver-loading APIs from user-mode binaries.
Baseline kernel crash telemetry and alert on repeated bug checks originating from the same host or user session.

Monitoring Recommendations

Ingest Windows Security, Sysmon, and kernel crash telemetry into a centralized analytics platform for cross-host correlation.
Enable Attack Surface Reduction (ASR) rules and audit token manipulation and process-injection events.
Track Patch Tuesday deployment status per host to identify systems still exposed to CVE-2025-27739.

How to Mitigate CVE-2025-27739

Immediate Actions Required

Apply the April 2025 Windows security updates from Microsoft to all affected client and server SKUs.
Prioritize patching on multi-user systems, terminal servers, and jump hosts where local users are common.
Restrict interactive and remote local logon rights to the minimum set of accounts required for operations.
Audit for local accounts and stale credentials that could provide the initial low-privileged foothold.

Patch Information

Microsoft addressed CVE-2025-27739 in the April 8, 2025 security updates. Refer to the Microsoft Security Update Guide for CVE-2025-27739 for the KB numbers that map to each affected Windows 10, Windows 11, and Windows Server build. Install the cumulative update that corresponds to the specific OS version, then reboot to complete kernel patching.

Workarounds

No official workaround is documented by Microsoft; applying the security update is the supported remediation.
Enforce the principle of least privilege and remove unnecessary local logon rights until patches are deployed.
Enable Credential Guard and Hypervisor-Protected Code Integrity (HVCI) to raise the cost of kernel-mode compromise.
Isolate unpatched systems from sensitive network segments and monitor them with elevated logging until updates land.

bash

# Verify installation of the April 2025 cumulative update on Windows
wmic qfe list brief /format:table

# PowerShell equivalent to check for installed KBs
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20