To install the September 2026 Exchange Server V2 security update, first identify the server’s Exchange generation and cumulative update (CU), then obtain the matching V2 package from Microsoft and follow its specific KB instructions. Restart before and after installation, then verify the build and security update detection with Exchange Health Checker, check Exchange services, and test Outlook on the web (OWA) and the Exchange admin center (EAC).
“V2” alone is not enough to identify an installer: Microsoft has used that label for other releases. The September 2026 V2 release adds coverage for CVE-2026-96940 compared with the original September release. Microsoft says September 2026 updates for Exchange Server 2016 and 2019 are available only to Period 2 Extended Security Update (ESU) program customers. See Microsoft’s September 2026 release announcement and confirm the package identity on the applicable KB page before installing.
Identify the exact Exchange V2 update you need
Start with the Exchange generation and CU installed on each server. The available packages and their applicability depend on those details; an update for a different CU may fail to install. Use Exchange Health Checker to inventory the servers, record their build numbers, and note any detected interim update (IU) or security hotfix.
Microsoft recommends Health Checker to identify servers that are behind on CUs or security updates, or that need manual actions. Its update FAQ also recommends installing security updates on Exchange Management Tools-only machines.
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- For Exchange Server Subscription Edition (SE), select the package for the installed SE CU.
- For Exchange Server 2019 or 2016, confirm the server’s CU and that your organization is enrolled in Period 2 ESU. Microsoft says updates released for these editions between May and October 2026 are limited to Period 2 ESU customers.
- Use Microsoft’s current release announcement and the KB/download page matching the edition and CU. Do not select a package merely because its name contains “V2.”
The build table retrieved for this release lists September 2026 values for SE RTM and Exchange 2019 CU15, but it does not establish whether those values distinguish the V2 re-release. Exact Exchange 2016 and 2019 V2 KB/build combinations should therefore be taken from the matching Microsoft KB, not inferred from a general build table. Microsoft’s Exchange build numbers and release dates can help with edition and CU comparisons.
Prepare for installation
Schedule a maintenance window appropriate to the server’s role, workload, and Exchange topology. Review the prerequisites and installation directions in the KB for the selected package. Follow your organization’s normal backup and operational safeguards; requirements can differ by environment.
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Microsoft recommends restarting the Exchange server before applying an update and restarting it afterward, even if the installer does not request a restart. Plan for both restarts rather than treating the installer’s final dialog as proof that the server is ready.
Install the matching package
- Download the V2 package from the Microsoft route specified by its release announcement or matching KB. Verify that the KB applies to the server’s Exchange edition and CU.
- Run the package using the administrative rights and exact procedure in that KB. There is no single installer command to assume for every Exchange generation and package.
- When setup completes, restart the server.
- Check that Exchange services have started properly before returning the server to normal service.
Verify that the update installed
Check Health Checker’s update detection
Run Exchange Health Checker again after installation. In its Exchange Information section, inspect Build Number and Exchange IU or Security Hotfix Detected. Review any remaining manual actions it reports. The build and detected-update fields provide complementary evidence; do not rely on a success message alone.
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Check the executable version against the correct CU
In Exchange Management Shell, run Microsoft’s documented command:
Get-Command Exsetup.exe | ForEach-Object {$_.FileVersionInfo}Compare the resulting file version with the build entry for the server’s specific Exchange generation and CU. The build table lists Exchange SE RTM’s September 2026 SU as 15.2.2562.49 (15.02.2562.049) and Exchange 2019 CU15’s September 2026 SU as 15.2.1748.51 (15.02.1748.051). Those entries alone do not establish that the V2 re-release is installed, so confirm the exact V2 package and expected result against its matching KB.
Get-ExchangeServer | Format-List Name,Edition,AdminDisplayVersion reports Exchange server and CU information, but it does not establish the installed SU or hotfix status by itself.
Confirm service and application health
Confirm Exchange services are started and test OWA and EAC. To confirm remediation of a specific vulnerability, check the matching KB or the Microsoft Security Update Guide entry for that CVE. A general build display alone is not proof of CVE coverage if Microsoft specifies additional steps.
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Troubleshoot installation and access failures
Installer says the upgrade patch cannot be installed
If Windows Installer reports that the upgrade patch cannot be installed because the target program may be missing or a different version, compare the server’s installed CU with the package’s intended CU. Microsoft identifies a CU/SU mismatch as a cause. Obtain the update that corresponds to the installed CU, or bring the server to the CU required by the applicable package.
OWA or EAC returns HTTP 500 after the update
Microsoft’s recovery guidance for post-update HTTP 500 errors documents reinstalling the security update from an elevated command prompt, restarting the server, and testing access again. If EAC still fails, the recovery article also covers reviewing the EAC virtual directory’s BinsearchFolder paths, running UpdateCas.ps1 and UpdateConfigFiles.ps1, running iisreset, and restarting. Use paths appropriate to the actual Exchange installation; example paths in the article are not universal.
Read Microsoft’s OWA/ECP HTTP 500 recovery procedure before changing virtual-directory settings or running its scripts.
Update was interrupted or services remain stopped
For an interrupted update that leaves services stopped or disabled, use Microsoft’s failed-update troubleshooting guidance and review the Exchange setup logs. Restore only services that were active before setup; POP3 and IMAP4 are normally disabled unless your environment uses them. See Microsoft’s Exchange security update troubleshooting guidance.
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