Article
May 2026 Patch Tuesday: Key Vulnerabilities Overview
Introduction
Microsoft’s May security update addresses over 160 vulnerabilities, including several critical issues.
Many of these flaws, particularly those allowing remote code execution and affecting platforms like Microsoft SharePoint and Defender, could be exploited by attackers to compromise your business.
Importantly, some of these vulnerabilities are potentially exploitable over the internet, making prompt updates essential. In this article, we provide an overview of this month’s patches and highlight the most notable security issues that require immediate attention.
Summary of May 2026 Patch Tuesday
This month’s Patch Tuesday focuses on fixing vulnerabilities in Microsoft products that affect many users worldwide. Notable issues include critical problems in Windows DNS Client and Azure DevOps that could potentially be exploited over the internet. These updates target serious risks like unauthorized access and data breaches. Staying informed and applying these updates promptly can help protect against cyber threats.
Understanding these updates is crucial in protecting enterprise environments. Below, we categorize the vulnerabilities based on their exposure to the internet.
Updates are listed according to their CVSS Score
Exposed to internet 
May 2026 Patch Tuesday
Internal Network
Exposed to the Internet
Windows DNS Client – Heap-based Overflow
The Windows DNS Client, responsible for resolving domain names to IP addresses on Windows systems, is vulnerable to a critical heap-based overflow. This flaw allows an attacker to exploit it by sending a specially crafted DNS response, potentially enabling remote code execution.
Azure DevOps – Information Disclosure
Azure DevOps, supporting developer collaboration and code repositories, has a critical information disclosure vulnerability. This results from inadequate access controls, potentially exposing sensitive information.
Microsoft SharePoint Server – Insufficient Access Controls
In Microsoft SharePoint Server, inadequate access controls allow an attacker with network access to execute code remotely. This vulnerability could be exploited by an authenticated attacker within the collaborative platform environment.
Microsoft Dynamics 365 (on-premises) – Code Injection
A critical code injection flaw in Microsoft Dynamics 365 (on-premises) allows authenticated users to execute arbitrary code over a network, posing serious risks in enterprise environments using these ERP and CRM applications.
M365 Copilot – Information Disclosure
An information disclosure vulnerability in M365 Copilot, an AI-powered assistant in Microsoft 365, could allow attackers to access sensitive information without authorization, compromising user productivity and privacy.
Internal Network
Windows Netlogon – Stack-based Buffer Overflow
Windows Netlogon, key for user authentication and network resource access, contains a stack-based buffer overflow vulnerability. This flaw could be exploited by an attacker through a crafted network request, allowing unauthorized remote code execution on a domain controller.
Microsoft Word – Use-After-Free
Microsoft Word, an essential application within Microsoft Office, is vulnerable to a use-after-free flaw. This allows attackers to execute code locally when exploited.
Microsoft Office – Use-After-Free
Microsoft Office, the popular suite of productivity applications, has a use-after-free vulnerability. This issue arises when processing certain exploit-craft files, leading to unauthorized code execution.
Windows GDI – Heap-based Buffer Overflow
The Windows Graphics Device Interface (GDI) has a heap-based buffer overflow vulnerability. Exploitability arises through crafted Enhanced Metafile (EMF) files, potentially leading to code execution.
Windows Event Logging Service – Elevation of Privilege
A vulnerability in Windows Event Logging Service allows potential attackers to elevate their privileges. This core component records system events and errors, crucial for monitoring and diagnostics.
Conclusion
In summary, May 2026 Patch Tuesday is a crucial reminder of the importance of keeping software updated. Protect your systems by ensuring updates are applied quickly. Regular vigilance and prompt action are the best defenses against cyber threats. Stay safe online by being proactive with security updates and avoiding suspicious online activities.
Have questions about implementing these patches or securing your IT environment? Schedule a call with At-Bay’s Advisory Services team to get started.
About CVSS
The Common Vulnerability Scoring System (CVSS) is an industry-standard framework for evaluating and communicating the severity of software vulnerabilities. It provides a numerical score that helps organizations prioritize and address security issues effectively. CVSS scores quantify the severity of a vulnerability on a scale from 0 (no severity) to 10 (critical severity). CVSS considers multiple factors, including; Exploitability, Impact, Exploit code maturity, Remediation level, Report confidence. The system enables organizations to compare and prioritize vulnerabilities based on their potential impact on IT infrastructure.
References
- https://www.bleepingcomputer.com/news/microsoft/microsoft-may-2026-patch-tuesday-fixes-120-flaws-no-zero-days/
- https://blog.talosintelligence.com/microsoft-patch-tuesday-may-2026/
- https://msrc.microsoft.com/update-guide/releasenote/2026-may
- https://www.helpnetsecurity.com/2026/05/12/microsoft-may-2026-patch-tuesday/
- https://www.zerodayinitiative.com/blog/2026/5/12/the-may-2026-security-update-review