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SQL Server 2017 CU31 + GDR SQL Server 2017 CU31 + GDR Security update
Patch Tuesday

KB5077471

KB5077471: Security update for SQL Server 2017, CU branch, March 2026. Merge replication flaw fixed; ALTER USER blocked for Administrator

In short

The update fixes two Important SQL Server elevation-of-privilege vulnerabilities, including publicly disclosed CVE-2026-21262. It also blocks ALTER USER when the target login is the system Administrator account.

Does it affect you? Applies to: Supported x64 installations of SQL Server 2017. The update is optional on computers that do not host SQL Server Reporting Services.

Build
14.0.3520.4
Servicing branch
CU
Security
2 fixed
Restart
Required

For servers on the CU branch: they install cumulative updates, which also bring fixes beyond security. Servers on the GDR branch (security fixes only) get a separate update. Which branch am I on?

What changes

Fixes 2 changes

Replication

  • The merge replication version upgrade process no longer has the elevation-of-privilege vulnerability addressed by this update.1
    Fixes an elevation-of-privilege vulnerability in the version upgrade process for merge replication.

Security Infrastructure

  • ALTER USER is blocked when the target login is the system Administrator account.2
    The hotfix blocks the ALTER USER operation when its target login is the system Administrator account.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-03-10
Classification
Security Updates
Type
Cumulative update
Servicing branch
CU
Restart
Required
Replaces
KB5068402, KB5065225, KB5063759, KB5058714
+5 earlier KB5050533, KB5046858, KB5046061, KB5042215, KB5040940
Replaced by
KB5084818
VersionBuildChannel
2017 14.0.3520.4 General availability

Security

2 vulnerabilities fixed
2 important
VulnerabilitySeverityCVSS
CVE-2026-21262
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important 8.8
CVE-2026-26115
SQL Server Elevation of Privilege Vulnerability
 Important 8.8

Downloads (Microsoft Update Catalog)

Package 2017
542.8 MB
sqlserver2017-kb5077471-x64.exe Main update · KB5077471 SHA-1: 058acbcb…8cc4b6

Updated components

131 files changed since the previous update for the same versions.

Top changed componentsFiles
SQL Server Engine94
SQL Server PolyBase3

Sources

Updated
Cited passages from Microsoft's official notes (2)
  1. 1. Fixes an elevation of privilege vulnerability in the version upgrade process for merge replication. support.microsoft.com
  2. 2. This hotfix blocks the ALTER USER operation if the target login is the system Administrator account. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 2 quoted passages · compared with Microsoft's page on Sep 26, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 5/5, clarity 4/5, completeness 4/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake