CVE-2026-50300: Windows 10 1607 Information Disclosure Flaw

CVE-2026-50300 Overview

CVE-2026-50300 is an integer underflow vulnerability in the Microsoft Windows Kernel that enables an authorized local attacker to disclose sensitive kernel memory contents. The flaw is tracked under [CWE-125] (Out-of-bounds Read) and stems from arithmetic wraparound during kernel-mode processing. Microsoft published the advisory on July 14, 2026, covering supported client and server editions of Windows 10, Windows 11, and Windows Server.

An attacker with valid local credentials can trigger the underflow to read memory outside intended boundaries. Successful exploitation exposes kernel data such as pointers, tokens, or other artifacts that assist follow-on privilege escalation attempts.

Critical Impact
A local authenticated attacker can read sensitive kernel memory, providing information useful for bypassing kernel address space layout randomization (KASLR) and chaining subsequent privilege escalation exploits.

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
Microsoft Windows 11 (24H2, 25H2, 26H1)
Microsoft Windows Server 2016, 2019, 2022, and 2025

Discovery Timeline

2026-07-14 - CVE-2026-50300 published to NVD
2026-07-16 - Last updated in NVD database

Technical Details for CVE-2026-50300

Vulnerability Analysis

The vulnerability resides in the Windows Kernel and is classified as an integer underflow that leads to an out-of-bounds read [CWE-125]. When kernel code performs unsigned arithmetic on a length or offset value that becomes smaller than expected, the subtraction wraps around to a very large positive value. Subsequent memory operations use that wrapped value as a bounds parameter, causing the kernel to read past the end of the intended buffer.

The impact is confidentiality-only: integrity and availability remain unaffected. Disclosed memory can include kernel pointers, cryptographic material, or fragments of other processes' data residing in kernel-managed pools.

Root Cause

The root cause is missing validation of a size or index computation before it is used to bound a read operation. A crafted input causes an intermediate calculation to underflow, and the resulting oversized value is passed to a copy or read routine that trusts the caller-influenced length.

Attack Vector

Exploitation requires local access with low privileges. The attacker executes code on the target system, typically as a standard user, and invokes the vulnerable kernel path through a system call, IOCTL, or similar interface. No user interaction is required. Because no verified proof-of-concept has been published, technical specifics on the affected kernel routine are limited to Microsoft's advisory.

Refer to the Microsoft CVE-2026-50300 Advisory for vendor-supplied technical details.

Detection Methods for CVE-2026-50300

Indicators of Compromise

Unexpected user-mode processes issuing repeated IOCTL or NT system calls to kernel components not typical for that workload.
Kernel-mode exceptions or bugchecks generated during suspicious user-mode activity, indicating probing of the vulnerable code path.
Presence of unsigned or newly introduced binaries executing on systems missing the July 2026 cumulative update.

Detection Strategies

Monitor Windows Event Log channels for kernel error events (Event ID 41, Event ID 1001) correlated with unprivileged process activity.
Use EDR telemetry to identify processes spawning unusual syscall patterns targeting the Windows Kernel from low-integrity contexts.
Baseline expected IOCTL usage per host and alert on deviations, particularly from user-writable directories such as %TEMP% or %APPDATA%.

Monitoring Recommendations

Track patch compliance across all Windows 10, Windows 11, and Windows Server hosts listed in the advisory.
Enable kernel audit policies and forward events to a centralized SIEM for correlation with authentication and process telemetry.
Monitor for post-exploitation behavior such as token manipulation, credential access, or lateral movement following suspicious kernel interactions.

How to Mitigate CVE-2026-50300

Immediate Actions Required

Apply the July 2026 Microsoft security update to all affected Windows client and server systems without delay.
Prioritize patching on multi-user systems, terminal servers, and jump hosts where local access is more broadly available.
Audit local account usage and remove unnecessary interactive logon rights for standard users on sensitive systems.

Patch Information

Microsoft addressed CVE-2026-50300 in the security updates referenced in the Microsoft CVE-2026-50300 Advisory. Administrators should deploy the corresponding cumulative update for each affected Windows build via Windows Update, WSUS, Microsoft Update Catalog, or their configured patch management platform.

Workarounds

No official workaround has been published by Microsoft; installing the security update is the supported remediation.
Enforce least privilege by restricting local logon and removing administrative rights from standard user accounts.
Enable attack surface reduction rules and application control policies to limit execution of untrusted binaries that could deliver a local exploit.

bash

# Verify installed updates on a Windows host
wmic qfe list brief /format:table

# PowerShell: check for the latest cumulative update KB
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10