October Patch Tuesday: 1,408 CVEs, 1 exploited flaw and a SharePoint surprise
Microsoft’s October 2026 Patch Tuesday is the year’s largest release, with 1,408 CVEs requiring customer action, 72 of them rated critical. September, the previous high, carried 963. One CVE is already exploited: CVE-2026-96951, a Windows Shell flaw that bypasses Mark of the Web. Two were publicly disclosed before release, in the .NET Framework and the MessagePack-CSharp library. Separately, on 25 September Microsoft reported attacks against CVE-2026-65660, a SharePoint Server flaw fixed in August. Readiness recommends a Patch Now scheduling for Windows, Office, Exchange and the developer tooling, and a standard release schedule for SQL Server. The Readiness team has published an infographic summarising deployment risk by product family.
Known issues
On 14 October, Microsoft added a known issue to this month’s Windows 11 updates, KB5127648 for versions 24H2, 25H2 and 26H2, and KB5127646 for 26H1. Non-admin users might be unable to open Remote Desktop connections to devices that have Administrator protection enabled, with error 0xC000000D. The issue started with September’s non-security preview update. The Windows 11 security baselines enable Administrator protection by default, so test remote access to managed hosts before broad deployment. Microsoft’s mitigation is to turn off Administrator protection temporarily through your policy management tool, and a fix will follow in a future update.
Two issues remain open:
Some USB Audio Class 1.0 devices might fail to start or produce no sound. The 14 September out-of-band update resolved part of this, and for the remaining symptoms Microsoft directs IT administrators to Microsoft Support for Business.
Windows Server Update Services still does not display synchronisation error details on Server 2025 and Server 2022. Microsoft removed the function to address CVE-2025-59287 and offers no workaround.
And three are now closed:
The incorrect “Microsoft Defender Antivirus is turned off” notifications, still open when we published in September, were fixed by Defender Antivirus update 4.18.26080.4, released on 17 September.
On Windows 11, the October update fixes Explorer failing to start after sign-in on multi-user systems such as Azure Virtual Desktop with FSLogix, which left users at a black screen.
On Windows 10, Windows 11 23H2 and Server 2016 and 2019, it fixes File History failing to back up or restore and showing a false “Reconnect your drive” message.
Major revisions and mitigations
Between the September and October releases, from 9 September to 12 October, Microsoft’s Security Update Guide notifications covered 111 entries for Microsoft’s own products, not counting Chromium republications for Edge. Of those 111, 90 are true revisions rather than new entries. September’s window had one.
On 17 September, 84 of September’s CVEs gained Office for Mac updates. Each revision note tells customers running affected Mac software to “install the update for their product to be protected”.
On 16 September, Microsoft corrected the scoring of three critical SQL Server remote code execution flaws from September, CVE-2026-67378, CVE-2026-67631 and CVE-2026-67643. The scores now record that “an attacker does not require any privileges”. Microsoft calls this an informational change.
On 25 September, Microsoft revised CVE-2026-65660, a SharePoint Server remote code execution flaw fixed in August, to state that it “had reliable evidence of observed attacks against exploitation of this vulnerability”. CISA added it to its list of known exploited vulnerabilities the same day. The Security Update Guide still shows “Exploited: No” for this CVE, so a report filtered on that flag will miss it. If any SharePoint server lacks the August update, install it now.
Of the 21 new entries, 18 are critical cloud-side flaws in Azure, Microsoft 365 Copilot, Dataverse and Fabric, all marked “Customer action required: No”. Two are Edge flaws, and one is CVE-2026-96940 in Exchange Server, published on 2 October and covered below.
Microsoft has published no mitigations and no workarounds in the October release.
Windows lifecycle and enforcement updates
These support milestones passed with this release on 13 October, as scheduled:
Office 2021 retail and Office LTSC 2021, including Skype for Business LTSC 2021, reached the end of support.
Windows 10 Enterprise 2016 LTSB and Windows 10 IoT Enterprise LTSB 2016 reached the end of extended support.
Extended Security Updates for Windows Server 2012 and 2012 R2 ended. Year three was the last, so the October update is the final one for both.
Windows 11 Home and Pro version 24H2 reached the end of updates.
Windows Server 2022 moved to extended support, which runs to 14 October 2031.
The next milestones fall on 10 November 2026, the date of November’s Patch Tuesday. .NET 8 and .NET 9 reach the end of support, as do PowerShell 7.4 and 7.5. Windows 11 Enterprise and Education 23H2, and IoT Enterprise 23H2, reach the end of updates, and Microsoft says November’s update “will be the last update available for these editions”.
Microsoft also starts or tightens several enforcement changes with this release:
Windows 11 24H2, 25H2 and 26H2, and Windows Server 2025, now restrict NTLMv1-derived credentials for single sign-on by default. Where Credential Guard is off, Microsoft warns this “might affect Wi-Fi, Ethernet and VPN connections that use MS-CHAPv2-based authentication” (KB5066470).
AD FS Distributed Key Manager container permissions move into enforcement mode. Supported servers remediate automatically, but Server 2012 and 2012 R2 need manual remediation (KB5121391).
ReFS volumes on removable media enter an audit phase, and blocking is enabled by default from the January 2027 update (KB5130741).
The Windows Production PCA 2011 Secure Boot certificate, used to sign the Windows boot loader, expires on 19 October. Devices without its replacement, Windows UEFI CA 2023, keep starting and updating normally, but they stop receiving new early-boot protections (KB5062710).
Microsoft’s test guidance for this release runs to 496 Windows entries, 41 of them flagged as high risk, against 466 and 55 in September. Printing, scanning and font rendering account for 31 of the 41. The Readiness team recommends these testing priorities:
Printing. Print documents with mixed fonts from 32-bit and 64-bit applications to physical and virtual printers. Add network printers by discovery and by IP address, and print through a shared print server, a USB printer and a PostScript driver.
Downloaded files. The exploited Shell flaw bypasses Mark of the Web, so open files and shortcuts downloaded from the internet and confirm the SmartScreen and security warnings still appear.
Remote access. Test Remote Desktop with a non-admin account against hosts that have Administrator protection enabled, and test Wi-Fi and VPN connections that use MS-CHAPv2.
Application installs. Install, repair and uninstall a representative set of MSI packages, including packages with script custom actions. Windows Installer takes 38 fixes this month.
Network servers. Run DNS servers (52 fixes) and DHCP servers (18) under load, and confirm leases, zone transfers and conditional forwarders behave as before.
Each month, we break down the update cycle into product families, as defined by Microsoft, with the following groupings.
Browsers
For the third month in a row, Microsoft’s Patch Tuesday release lists no browser CVEs. Edge security fixes arrived between releases instead. Between 9 September and 12 October, Microsoft published 414 CVEs for Microsoft Edge in the Security Update Guide: 409 republished from Chromium and five specific to Edge. None carries an exploited flag, and no Edge release in that period reported an exploit in the wild.
Microsoft Windows
Windows takes 1,122 CVEs this month, 42 of them critical. Elevation of privilege accounts for 617 entries, information disclosure for 200 and remote code execution for 179. Of the 42 critical entries, 31 are remote code execution, nine are elevation of privilege and two are spoofing.
The exploited flaw is CVE-2026-96951, a Windows Shell security feature bypass that evades Mark of the Web defences. An attacker must convince a user to open a crafted file or follow a link. CISA added it to its list of known exploited vulnerabilities on 13 October, with a remediation date of 16 October.
DHCP takes 18 fixes, six of them critical remote code execution: five in DHCP Server and one in the DHCP client. DNS Server takes 52, 10 of them remote code execution, though none is critical. Critical remote code execution also affects Hyper-V, Message Queuing, Microsoft QUIC, the Remote Desktop Gateway, Windows Deployment Services, Active Directory Domain Services, NDES and the multicast transport driver.
In file and image handling, the Raw Image Extension has three critical fixes, one of them a CVE assigned by Cisco Talos, and the PostScript printer driver takes three more. Text shaping takes two, and Media Foundation, the codecs library, the video decoder, GDI+, the graphics component and the Windows PDF component take one each.
The virtualisation-based security enclave takes eight fixes, five of them critical elevation of privilege.
The most-patched areas are DNS Server at 52, Win32k at 48, the Windows Kernel at 46 and Windows Installer at 38.
Add this Windows update to your Patch Now schedule. Every client needs the fix for the exploited Shell flaw, and DHCP servers and Hyper-V hosts need the critical server-side fixes.
Microsoft Office
Microsoft released 180 Office CVEs this month, 26 of them critical, and remote code execution accounts for 107.
Client updates on Windows are Click-to-Run only, for Microsoft 365 Apps, Office LTSC 2021 and Office LTSC 2024. Office for Mac updates ship in the same release this month, rather than nine days later as they did in September. Excel takes 69 fixes, 11 of them critical. Word takes 22, Access 13, Outlook 10 with five critical, PowerPoint nine with four critical, and Visio three, all critical.
SharePoint Server Subscription Edition takes 34 CVEs in KB5002927, two of them critical. SharePoint Server 2016 and 2019 left extended support on 14 July 2026, and two of this month’s flaws list them as affected with no update: CVE-2026-69943 for both versions and CVE-2026-97783 for 2019.
Office Online Server takes 43 CVEs in KB5002928. Skype for Business Server takes three, in KB5132779 for 2015 CU13, KB5131693 for 2019 CU8 and KB5131692 for Subscription Edition CU1.
Add these updates to your Patch Now schedule, because 25 of the 26 critical entries affect Excel, Outlook, PowerPoint, Visio and Word.
Microsoft Exchange and SQL Server
Exchange has one critical entry this month and SQL Server has none.
Exchange Server has seven CVEs across 2016 CU23, 2019 CU14 and CU15, and Subscription Edition: one critical remote code execution, CVE-2026-70571, five elevations of privilege and one spoofing flaw. Six are fixed by the 13 October updates: KB5128895 for Subscription Edition, KB5128896 for 2019 CU15, KB5128897 for 2019 CU14 and KB5128898 for 2016 CU23.
The seventh, CVE-2026-96940, was published on 2 October. Microsoft lists it against a separate set of updates released that day, KB5129955 to KB5129958, not against the 13 October updates, so confirm both sets are installed. Microsoft rates both CVE-2026-96940 and the critical entry as “Exploitation More Likely”..
SQL Server has 22 CVEs, none of them critical: eight remote code execution, seven elevation of privilege, four information disclosure and three denials of service. Each supported branch gets a cumulative update and a GDR: 2025 (KB5126967, KB5128492), 2022 (KB5126934, KB5128493), 2019 (KB5128494, KB5128495) and 2017 (KB5128496, KB5128497).
Exchange goes on the Patch Now list. SQL Server goes on the Schedule list because none of its 22 entries is critical. If September’s SQL Server update is still outstanding, install it first.
Microsoft Developer Tools
Microsoft released 66 CVEs across its developer tooling this month: two critical, 63 important and one moderate. Remote code execution accounts for 18 entries and elevation of privilege for 13.
Both critical entries also affect Windows. CVE-2026-105016 is a remote code execution flaw in Microsoft QUIC that needs no authentication or user interaction, and it affects .NET 8, 9, 10 and 11 on Windows and Visual Studio 2022 and 2026. CVE-2026-96222 is an AD FS certificate validation flaw that Microsoft lists against both the .NET Framework and Windows Server.
Two entries were publicly disclosed before release. CVE-2026-108398 in the .NET Framework lets an authenticated attacker bypass Windows Defender Application Control. CVE-2026-92707, a denial-of-service vulnerability in the MessagePack-CSharp library assigned by GitHub, affects Visual Studio and the ASP.NET Core SignalR MessagePack protocol.
Visual Studio Code has 10 fixes, five of them security feature bypasses, and PowerShell 7.4, 7.5 and 7.6 take two.
Add these updates to your Patch Now schedule, starting with the .NET updates that carry the QUIC fix.
Adobe (and third-party updates)
Adobe published 11 security bulletins on 13 October, covering 175 CVEs across ColdFusion, Experience Manager, Commerce, Photoshop, Bridge, FrameMaker, Dimension, the Substance 3D tools and the Content Credentials SDK. None is rated priority 1, and Adobe is not aware of exploits for any of them. No Acrobat or Reader security update for this month. I mentioned last month that we are in for a few months of extraordinary patch releases. Harking back to 2003 (when I started work on the nascent field of Microsoft patch management), with Microsoft releasing just 51 updates, anything over a 1000, much less 1400 CVE entries would have been unimaginable. I don’t think that we are at a “patch maximum” yet — but I hope that things calm down soon.ComputerworldRead More