CVE-2026-55040 in Microsoft SharePoint Server
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Quick answer
Microsoft SharePoint Server should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- SharePoint Server before 16.0.19725.20434
- SharePoint Server 2016
- SharePoint Server 2019
Fixed versions
- SharePoint Server 16.0.19725.20434 or later
How to fix it
CVE-2026-55040 is a authorization bypass issue in Microsoft SharePoint Server. Update from SharePoint Server before 16.0.19725.20434 to SharePoint Server 16.0.19725.20434 or later or newer. Keep it simple: upgrade first, then test the normal user flow.
- Find every place where Microsoft SharePoint Server is installed or used.
- Upgrade Microsoft SharePoint Server to SharePoint Server 16.0.19725.20434 or later or a newer fixed release from the vendor.
- If you cannot upgrade right away, limit access to the affected feature until the update is done.
- Restart or redeploy the service if the product needs it after the update.
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Verify the fix
- Confirm the installed version is SharePoint Server 16.0.19725.20434 or later or newer.
- Run a normal login, admin, and user flow to make sure the site still works.
- Check logs for new errors after the update.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-55040?
Microsoft SharePoint Server versions listed as affected should be reviewed: SharePoint Server before 16.0.19725.20434, SharePoint Server 2016, SharePoint Server 2019.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.