For May, Patch Tuesday means 139 updates — but no zero-days

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Microsoft this week released 139 updates affecting Windows, Office, .NET, and SQL Server (though there were no updates for Microsoft Exchange Server). Despite the absence of zero-days, the May Patch Tuesday update still requires Patch Now recommendations for Windows and Office. 

The combination of three unauthenticated network RCEs (Netlogon, DNS Client, and SSO Plugin for Jira and Confluence), four Word Preview Pane RCEs, the large TCP/IP vulnerability cluster, and the carry-over BitLocker recovery condition (still active on Windows 10 and Windows Server) warrants an accelerated deployment release schedule. The Readiness team suggests that testing start with internet-facing services, domain controllers, and Office endpoints. The May 2026 Assurance Security Dashboard breaks the cycle down by Microsoft product family for deployment risk assessment.

(More information about recent Patch Tuesday releases is available here.)

Known issues

Patch Tuesday arrived this month with a clean bill of health (at least with respect to reported and known issues) for Windows 11 24H2, 23H2, Windows 10 22H2, and Windows Server 2025. However, two items warrant attention.

Issues resolved

  • KB5089549 for Windows 11 25H2 and 24H2 resolves the April PCR7/BitLocker recovery condition and improves Boot Manager servicing so subsequent boot file updates do not trigger recovery.
  • Secure Boot certificate distribution adds a new C:\Windows\SecureBoot folder of automation scripts for IT teams rolling out the Windows UEFI CA 2023 key replacement under CVE-2023-24932, ahead of the 2011 certificate expirations happening between June and October 2026.
  • Simple Service Discovery Protocol (SSDP) notification reliability improves, so the service is less likely to become unresponsive under sustained load; this is relevant to networks running UPnP device discovery.

Major revisions and mitigations

Given this month’s Preview Pane issues, Microsoft offered mitigation advice:

Windows lifecycle and enforcement updates

We’ve mentioned the CA certificate issue before, but it’s worth flagging again as we approach the EOS and enforcement dates for:


Each month, the team at Readiness provides detailed, actionable testing guidance for Patch Tuesday releases. This guidance is based on assessing a large application portfolio and a comprehensive analysis of the patches and their potential impact on Windows platforms and application deployments.

This month’s Patch Tuesday flags two components as high-risk: the Ancillary Function Driver for WinSock, with an explicit Bluetooth focus, and the Telnet client. Microsoft also ships a pre-release security fix to the Common Log File System driver, and Secure Boot key rolling continues under CVE-2023-24932. TCP/IP is the most-patched component this cycle, with 11 separate updates. Lower-risk patches involve graphics, storage, virtualization, VPN, and Office MSI editions.

Ancillary Function Driver for WinSock 

The WinSock kernel driver (afd.sys) mediates every TCP and UDP socket on Windows, and the May update lands a regression-sensitive change to the Bluetooth interaction path. Failure here typically surfaces as audio dropouts, paired-device drops on sleep, slow reconnect on Wi-Fi handover, or a clean AFD-referenced bug check during sustained load. Watch the System event log for new errors from AFD, TCP/IP, or BTHUSB sources during your test window.

Success in testing these drivers looks silent: no stutters, no event-log churn, no handle leaks.

Your testing regime should include:

  • Browse the web over HTTP and HTTPS on both IPv4 and IPv6; download a multi-gigabyte file and verify it completes without stalls.
  • Establish a Remote Desktop session, idle 30+ minutes, then resume; place a Teams call with audio, video, and screen share.
  • Disable and re-enable the NIC, switch between Wi-Fi and Ethernet, and sleep/resume the machine; expect the network to return cleanly with no AFD-referenced bug check.
  • Toggle Bluetooth on and off from Settings and Action Center; pair and unpair headphones, mouse, keyboard, and phone, repeating through several cycles.
  • Play audio over a Bluetooth headset for 10+ minutes during a Teams call; expect zero dropouts and clean mic/speaker switching as devices toggle.
  • Transfer a file to and from a phone over Bluetooth; connect a Bluetooth keyboard and mouse, leave idle, and resume input.
  • Sleep and resume the machine with Bluetooth peripherals connected; verify they reconnect without manual intervention.

Telnet client

The Telnet client (telnet.exe) is an optional Windows feature, rarely enabled on modern endpoints. The high-risk flag matters wherever the feature is installed. Check first with Get-WindowsCapability -Online -Name “Telnet.Client~~~~0.0.1.0”. If installed, launch telnet.exe against a known good endpoint and confirm it opens, accepts input, and exits cleanly. If the feature is not in use, treat this update as an opportunity for attack-surface reduction and remove it.

Common Log File System security fix

Microsoft corrected two integer underflow vulnerabilities in the CLFS driver (clfs.sys) that could trigger a system crash or elevation of privilege. Regression risk is low, but CLFS underpins transaction logging across SQL Server, DTC, Failover Clustering, Hyper-V, Active Directory, and Event Log. Validate where these run. A bug check referencing clfs.sys after the update is the clearest red flag.

  • Reboot, run a representative workload for 24 to 48 hours, and check System and Application logs for new errors referencing CLFS, NTFS, DTC, or FailoverClustering.
  • On SQL Server, restart the service, run standard transactions, perform a backup and restore, and confirm Always On replication stays healthy.
  • Patch each cluster node, verify all nodes return as Up, and move a clustered role across nodes.
  • On a patched domain controller, run repadmin /replsummary and dcdiag /v; verify Group Policy still applies on clients.
  • Confirm VSS writers report Stable via vssadmin list writers, then run a full backup and a test restore.

Secure Boot and BitLocker

Secure Boot validation continues under the CVE-2023-24932 key rolling work. The risk is a recovery prompt or an unbootable device. Run only on dedicated test machines with the recovery key backed up.

  • Enable BitLocker on the OS drive, verify TPM protectors with manage-bde -protectors -get c:, then disable and confirm clean decryption.
  • With Secure Boot enabled, trigger recovery via reagentc /boottore 1, unlock with the recovery key, and verify normal next boot.
  • With both enabled, apply the Windows UEFI CA 2023 key update and confirm the system boots without a recovery prompt.
  • Hibernate with Secure Boot and BitLocker on (powercfg /hibernate on, shutdown -h), then resume and confirm no recovery screen.

Other Windows components

TCP/IP has the highest patch volume; the rest receive routine updates with no functional changes.

  • Networking: run sustained file transfers, VPN sessions, and stable throughput over IPv4 and IPv6 to cover tcpip.sys (six updates), the Native Wi-Fi driver, and the LLDP driver.
  • VPN and filtering: exercise IKEv2 tunnels through sleep/wake and verify Windows Firewall rules to cover IKEEXT.dll and BFE.
  • Graphics and shell: run sustained UI activity and GPU-accelerated workloads to cover the Desktop Window Manager, graphics memory manager, and the graphics kernel; watch for artifacts or flickering.
  • Virtualization: exercise VM start/save/resume/stop and external/internal/private virtual switches to cover Hyper-V vmswitch.sys.
  • Storage and sync: exercise cloud sync hydration, Storage Spaces pool operations, and RDP printer/clipboard redirection.

Microsoft Office and SharePoint

This month’s Office updates target MSI editions only: Excel 2016 (KB5002865), Word 2016 (KB5002858), Office 2016 shared libraries (KB5002866), and SharePoint Server 2016, 2019, Online Server, and Subscription Edition. Click-to-Run estates are unaffected.

  • Open complex Excel workbooks with formulas, macros, and external data connections; save and reopen to verify integrity.
  • Edit Word documents with embedded objects, tracked changes, and complex formatting.
  • Across patched SharePoint editions, validate document library operations, co-authoring, and workflow execution.
  • Confirm that Office add-ins and line-of-business integrations continue to operate.

The Readiness team recommends testing start with the high-risk items. The WinSock driver update warrants a Bluetooth-heavy regression pass across peripherals, audio, file transfer, and sleep/wake. The Telnet client flag is narrow but applies wherever the optional feature is enabled. The CLFS security fix is low regression risk, but its blast radius is wide: validate SQL Server, failover clusters, Hyper-V, Active Directory, and event logging where they exist. Secure Boot and BitLocker validation remains essential as CVE-2023-24932 key rolling continues. Microsoft Office is MSI-only this cycle.

Each month, we break down the update cycle into product families (as defined by Microsoft) with the following basic groupings: 

  • Browsers (Microsoft Edge) 
  • Microsoft Windows (both desktop and server) 
  • Microsoft Office
  • Microsoft Exchange and SQL Server 
  • Microsoft Developer Tools (Visual Studio and .NET)
  • Adobe (if you get this far) 

Browsers

For this Patch Tuesday, Microsoft Edge released the stable version (148.0.3967.54) on May 7, according to the Edge security release notes. This update cycle covers six Edge-engineered CVEs plus 127 Chromium upstream CVEs flowing through:

  • CVE-2026-33111 — Copilot Chat (Microsoft Edge) — Information disclosure (CVSS 7.5, rated critical). This is the headline browser issue this month.
  • CVE-2026-41107 — Microsoft Edge (Chromium-based) — Information disclosure (CVSS 7.4). External control of file name and path.
  • CVE-2026-42838 — Microsoft Edge (Chromium-based) — Elevation of privilege (CVSS 5.4). Injection in a downstream component.
  • CVE-2026-7896 through CVE-2026-8022 — Chromium upstream — 127 CVEs covering use-after-free, out-of-bounds read and write, type confusion, and integer overflow across V8, Blink, Skia, WebRTC, ANGLE, and DevTools. The same fixes ship in the Chrome Stable channel; see the Chrome releases blog for the upstream notes.

Add these updates to your Patch Now deployment schedule for Edge-managed environments.

Microsoft Windows

Microsoft addressed 67 unique vulnerabilities across Windows, six rated critical and 61, important. Elevation of privilege dominates by volume (44 entries), followed by remote code execution (9), denial of service (7), information disclosure (4), and security feature bypass (3). The six critical entries span six distinct Windows features:

  • CVE-2026-41089 — Windows Netlogon — Remote code execution (CVSS 9.8). Unauthenticated stack-based buffer overflow targeting domain controllers; the highest-impact Windows CVE this cycle.
  • CVE-2026-41096 — Windows DNS Client — Remote code execution (CVSS 9.8). Unauthenticated heap-based overflow in name resolution.
  • CVE-2026-40402 — Windows Hyper-V — Elevation of privilege (CVSS 9.3). The only non-RCE critical this cycle; guest-to-host escalation on virtualization hosts.
  • CVE-2026-40403 — Windows Graphics Component — Remote code execution (CVSS 8.8). Rendering-path RCE.
  • CVE-2026-35421 — Windows GDI — Remote code execution (CVSS 7.8). Exploitation via a malicious Enhanced Metafile (EMF) image opened in Microsoft Paint or any EMF-rendering application.
  • CVE-2026-32161 — Windows Native WiFi Miniport Driver — Remote code execution (CVSS 7.5). Wireless networking attack surface.

Domain controllers and Hyper-V hosts are the deployment priority, given Netlogon’s unauthenticated profile and the guest-to-host escape. Add this Windows update to your Patch Now deployment schedule.

Microsoft Office

Microsoft released 27 Office CVEs — nine critical, 18 important. Remote code execution dominates with 15 entries; the rest split across information disclosure (4), elevation of privilege (4), spoofing (3), and tampering (1).

SharePoint Server is the main priority, given the network-RCE profile — even with the authenticated-Site-Owner precondition. Office 2019 MSI estates pick up six critical fixes between the four Word RCEs and the two generic Office RCEs. The Team Events Portal CVE is addressed cloud-side — no on-premises action. Apply this month’s Office security updates (KB5002865, KB5002858, KB5002866, and the SharePoint set in Issues Resolved above) per the standard ring schedule.

Microsoft Exchange and SQL Server

This month, Microsoft SQL Server receives a single patch and Microsoft Exchange Server gets none:

  • CVE-2026-40370 — SQL Server — Remote code execution (CVSS 8.8). External control of file name or path allows an authenticated attacker to execute code over a network. The fix is broadly distributed across SQL Server 2025, 2022, 2019, 2017, and 2016 SP3 via both GDR and CU channels.

SQL Server estates should deploy via GDR or CU per their standard patching cadence, prioritizing internet-exposed instances given the post-authentication blast radius implied by the CVSS 8.8. Add this update to your Patch Now deployment schedule for any internet-connected SQL Server.

Developer tools

Microsoft released 11 CVEs across its developer tooling, with one update rated critical (for Azure DevOps) and 10 rated important, covering the following areas:

Add these Microsoft updates to your standard developer update release schedule.

Adobe (and third-party updates)

I keep promising that this section should be retired (and it should), but Microsoft released a sizable third-party sweep through Azure Linux 3.0 and CBL Mariner 2.0 this month: 191 open-source CVEs spanning the Linux kernel, the Go runtime, Apache httpd, PHP, CoreDNS, valkey, Ruby, gnutls, Apache Thrift across its Node.js, Rust, and Java implementations, plus vim, postfix, expat, nmap, Prometheus, KEDA, and PgBouncer. This is a lot for anyone.

In addition to all this, Microsoft issued a patch (CVE-2026-41103) for its own SSO Plugin for Jira and Confluence. This vulnerability allows an attacker to forge a Microsoft Entra ID identity via a crafted SAML response; patching requires updating the plugin within Atlassian rather than on a Microsoft platform. In other words, the Microsoft attack surface now extends to other vendors’ application stacks, with patching responsibilities split across vendors. 

With such diffusion of responsibility, what could go wrong?

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