Microsoft October 2026 Patch Tuesday fixes 1,411 flaws, 3 zero-days

Today is Microsoft's October 2026 Patch Tuesday, with security updates addressing a record-breaking 1,411 flaws, including one actively exploited and two publicly disclosed zero-day vulnerabilities.

This Patch Tuesday addresses 70 "Critical" vulnerabilities, 57 of which are remote code execution, 11 are elevation of privileges, and 2 are spoofing.

When BleepingComputer reports on Patch Tuesday security updates, we only count vulnerabilities released by Microsoft on Patch Tuesday itself.

Therefore, today's total excludes 348 flaws fixed earlier this month, including vulnerabilities in Azure API Center, Azure App Service, Azure Event Grid, Azure SRE Agent, Mariner, Microsoft Bookings, Microsoft Dataverse, Microsoft Exchange Server, and Microsoft Partner Center.

Microsoft announced today that Windows 11, version 24H2 Home and Pro, and Windows 10 Enterprise LTSB 2016 have reached end of support.

"Today, October 13, 2026, Windows 11, version 24H2 Home and Pro, and Windows 10 Enterprise LTSB 2016 have reached end of updates. The October 2026 monthly security update is the last update available for these editions," Microsoft said.

Earlier this month, Microsoft also said organizations running Windows 11 23H2 Enterprise, Education, and IoT Enterprise editions should upgrade to newer versions as they will no longer receive security updates starting next month.

This month's Patch Tuesday fixes one actively exploited and two publicly disclosed zero-day vulnerabilities.

Microsoft classifies a zero-day flaw as publicly disclosed or actively exploited when no official fix is available.

The actively exploited zero-day vulnerabilities addressed during this October 2026 Patch Tuesday are:

Microsoft patched an actively exploited zero-day security bypass flaw that allowed attackers to bypass the Mark of the Web security feature.

"Improper neutralization of special elements used in a command ('command injection') in Windows Shell allows an unauthorized attacker to bypass a security feature over a network," warns Microsoft.

No details have been shared on how attackers exploited the flaw or who disclosed it.

Microsoft has fixed a security feature bypass in the .NET Framework that can be exploited to run unauthorized applications.

"Untrusted search path in .NET Framework allows an authorized attacker to bypass a security feature locally," explains Microsoft.

Microsoft says this flaw could allow attackers to bypass Windows Defender Application Control (WDAC) enforcement and run unauthorized applications.

"An authenticated attacker could place a specially crafted .NET assembly on an affected system and register it for loading by a protected process." Microsoft says.

"Successful exploitation could bypass Windows Defender Application Control restrictions and allow the attacker to execute code within the protected process. User interaction is not required."

James Forshaw of Google Project Zero discovered the flaw.

Microsoft fixed a denial-of-service flaw in MessagePack-CSharp.

"Improperly controlled sequential memory allocation in .NET allows an unauthorized attacker to deny service over a network," explains Microsoft.

Microsoft has not shared who disclosed the vulnerability.

With this month's record-breaking number of vulnerabilities, Microsoft has also introduced a new method for organizations to prioritize security updates by grouping related flaws into what it calls "risk cohorts."

The new approach groups similar vulnerabilities together to help organizations better understand which security flaws pose the greatest risk to their systems and should be prioritized for patching.

Microsoft stressed that these groups do not necessarily indicate which flaws are the most dangerous, as the actual risk depends on whether they are being exploited in attacks, their severity, and how an organization uses the affected software.

Microsoft says the new approach is still experimental and is meant to help organizations prioritize security updates, not replace its existing patching recommendations.

Microsoft has published a PDF mapping the October 2026 vulnerabilities to their respective risk cohorts.

Below is the complete list of resolved vulnerabilities in the October 2026 updates. Note, this report does include the flaws fixed earlier this month.

To access the full description of each vulnerability and the systems it affects, you can view the full report here.