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Microsoft has released its November 2026 Patch Tuesday security updates, addressing 1,235 vulnerabilities across its products, including a Microsoft Outlook zero-day flaw actively exploited by cybercriminals to steal authentication credentials.
How Many Flaws Were Fixed?
The November security release addresses 66 critical vulnerabilities, including 48 remote code execution flaws, 15 elevation of privilege vulnerabilities and three use-after-free flaws affecting Microsoft Edge.
The updates also cover 536 elevation of privilege vulnerabilities, 296 remote code execution flaws, 157 information disclosure issues, 46 denial-of-service vulnerabilities, 27 security feature bypass flaws and 22 spoofing vulnerabilities. Another 142 vulnerabilities affect the Chromium-based Microsoft Edge browser. Approximately 639 of the reported flaws are associated with Windows or its components.
What Is the Outlook Zero-Day?
One of the most significant vulnerabilities addressed this month is CVE-2026-124194, a Microsoft Outlook spoofing flaw that attackers have already exploited.
The vulnerability allows an unauthenticated attacker to send a specially crafted message file and persuade a user to open it in an affected Outlook version. Opening the malicious file can cause Outlook to connect to an attacker-controlled network location without displaying its usual external-content warning.
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This connection may expose NTLM authentication information, potentially allowing criminals to impersonate users or gain unauthorised access to corporate accounts.
How Can Hackers Exploit It?
The attack relies on convincing users to open a malicious attachment, potentially delivered through a phishing email.
When the file is opened, Windows may automatically attempt to authenticate with a remote server controlled by the attacker. During this process, the user’s NTLMv2 authentication hash could be captured and potentially cracked offline.
If attackers recover usable credentials, they could attempt to access protected corporate resources and accounts without authorisation.
Why Are the Updates Significant?
Microsoft’s November release follows an even larger October 2026 Patch Tuesday, which addressed 1,411 vulnerabilities. The latest count excludes another 108 flaws fixed earlier in November, including issues affecting Entra Device Registration, Mariner and Microsoft Edge.
Microsoft has continued using artificial intelligence to identify and address vulnerabilities as part of its security improvement efforts. The scale of the updates reflects the extensive range of security weaknesses requiring attention across Microsoft’s software ecosystem.
Are Other Technology Companies Affected?
Several major technology vendors have also issued security advisories and patches during November. Google released emergency updates addressing an actively exploited Chrome zero-day vulnerability, while Cisco patched critical weaknesses affecting networking and security products.
Barracuda Networks, Ivanti, SonicWall and Zyxel also addressed vulnerabilities associated with reported attacks. SAP released fixes for four maximum-severity flaws, while Linux distributions issued updates addressing an OpenSSH authentication bypass vulnerability.
What Should Users Do?
The actively exploited Outlook vulnerability makes timely installation of security updates particularly important for individuals and organisations using Microsoft products. Affected users should apply the relevant security patches and exercise caution when opening unexpected email attachments.
Organisations should also review authentication security and ensure that supported Windows and Outlook installations receive the latest fixes. Microsoft’s November updates address a broad range of vulnerabilities, with the exploited Outlook flaw highlighting the continuing risks posed by credential theft and malicious attachments.
