CVE-2026-50300

What it actually does

CVE-2026-50300 is a local information disclosure vulnerability in the Windows Kernel caused by an integer underflow or wraparound condition. An attacker who already has local, authorized access can trigger the vulnerable kernel code path to cause incorrect size or boundary calculations, potentially exposing sensitive kernel or process memory. The stated security impact is loss of confidentiality only: the flaw does not directly provide code execution, privilege escalation, integrity modification, or denial of service, but disclosed memory may assist follow-on exploitation such as bypassing kernel address space protections or revealing secrets present in memory.

Why it matters to the business

This vulnerability can allow a low-privileged local user or malware already running on a Windows endpoint or server to obtain sensitive information from memory. By itself, it is not a remote compromise path, but it can materially increase the risk of a broader intrusion when chained with other vulnerabilities or post-compromise activity. Affected platforms include multiple Windows client and server releases, including Windows 10, Windows 11, Windows Server 2016, 2019, 2022, and 2025, so enterprise exposure may be broad. The CVSS score is moderate at 5.5, EPSS is currently low at 0.00298, it is not listed in CISA KEV, and no public exploit maturity is reported, so prioritization should focus on standard patch cycles unless high-risk shared systems, VDI, jump hosts, developer workstations, or servers allowing interactive local access are affected.

How an attack unfolds

An attacker first needs a foothold that permits local execution or interactive access on an affected Windows system, such as a compromised user account, malicious insider access, malware execution, or access to a multi-user host. The attacker then runs a local program that invokes the vulnerable Windows Kernel functionality with crafted values designed to trigger an integer underflow or wraparound. When the kernel mishandles the resulting calculation, memory that should not be exposed to the caller may be returned or made observable. The attacker can inspect the leaked data for sensitive material, kernel memory layout details, handles, tokens, pointers, credentials, or other secrets depending on what is present in memory. In a more advanced chain, the leak may be used to defeat address randomization or prepare a separate privilege escalation or code execution exploit.

How to fix it

Apply the Microsoft security update that addresses CVE-2026-50300 for all affected Windows versions: Windows 10 1607, 1809, 21H2, 22H2; Windows 11 24H2, 25H2, 26H1; Windows Server 2016, 2019, 2022, and 2025. No product-specific fixed build numbers were provided in the input, so use Microsoft Security Update Guide, Windows Update, WSUS, Microsoft Configuration Manager, Intune, or the relevant offline servicing channel to identify and deploy the appropriate cumulative update for each supported release. Where immediate patching is not possible, reduce risk by restricting local logon rights, limiting RDP and interactive access to servers, enforcing least privilege, blocking untrusted executable content, enabling endpoint protection, and prioritizing patching for shared systems and hosts exposed to many users. Because this is a kernel vulnerability, there is generally no reliable configuration-only mitigation that fully removes exposure short of installing the vendor fix.

How to confirm the fix worked

Confirm remediation by verifying that affected Windows systems have installed the applicable Microsoft cumulative security update released for this vulnerability or a later superseding update. Use centralized patch management compliance data, Windows Update history, WSUS or Configuration Manager reports, Intune device compliance, or local checks such as installed hotfix/package inventory and OS build revision comparison against Microsoft’s Security Update Guide. Validate that all in-scope Windows client and server versions are either patched, upgraded to a supported fixed release, or retired. For exposure validation, inventory systems running the affected Windows versions and identify those permitting local users, RDP access, shared desktop use, developer workloads, or third-party executable execution, as these are the most relevant attack surfaces for a local information disclosure flaw.

Typical attack path

1. Gain local access to an affected Windows workstation or server using valid credentials, malware execution, or an existing foothold.
2. Execute a local proof-of-concept or custom tool under a low-privileged user context.
3. Call the vulnerable Windows Kernel interface with crafted input that causes an integer underflow or wraparound.
4. Collect memory or kernel-derived information exposed by the vulnerable code path.
5. Analyze the disclosed data for secrets, pointers, memory layout information, or artifacts useful for lateral movement or exploit chaining.
6. Optionally combine the leak with another local privilege escalation or code execution technique to deepen compromise.

How to detect it

There are no specific public exploitation indicators provided for this vulnerability, and kernel information disclosure flaws often do not leave a distinctive log entry when triggered. To assess possible prior exploitation, focus on evidence of suspicious local code execution on affected and unpatched systems. Review endpoint detection telemetry, Sysmon, Windows Security logs, PowerShell logs, application control logs, and EDR process lineage for unusual binaries run by low-privileged users, especially from user-writable paths such as Downloads, Temp, AppData, Public, or Recycle Bin locations. Look for local exploit tooling, repeated crash or fault telemetry involving kernel-adjacent components, unexpected memory-dumping utilities, reconnaissance commands run immediately after local execution, and subsequent privilege escalation attempts. Correlate suspicious executions with the patch timeline and with systems that were unpatched at the time. Because no named threat actors, campaigns, or public exploit artifacts are provided, detection should be behavior-based rather than IOC-only.

• \AppData\Local\Temp\
• \AppData\Roaming\
• \Users\Public\
• \Downloads\
• \Windows\Temp\
• procdump.exe
• rundll32.exe
• powershell.exe -EncodedCommand
• cmd.exe /c whoami /priv
• whoami /all
• systeminfo
• tasklist /v
• handle.exe
• ProcessAccess
• MiniDumpWriteDump

What your security team should do

• Deploy the relevant Microsoft cumulative security updates across affected Windows client and server versions during the next standard patch cycle, with accelerated handling for shared servers, VDI, jump hosts, administrator workstations, and systems with many local users.
• Inventory affected Windows 10, Windows 11, and Windows Server versions and map patch compliance against Microsoft Security Update Guide entries for CVE-2026-50300 or later superseding updates.
• Restrict local and remote interactive logon rights on servers and high-value workstations to only required users and administrators.
• Use endpoint detection and application control to prevent untrusted local tools from executing, especially from user-writable directories.
• Monitor for suspicious local execution patterns, exploit testing activity, or post-exploitation behavior on unpatched systems, even though no public exploit or KEV listing is currently reported.
• Treat this vulnerability as higher priority if credible exploit code emerges, EPSS rises, it is added to KEV, or it is observed chained with local privilege escalation activity.