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CVE-2026-55040

Microsoft SharePoint Weak Authentication

9.1 CRITICALActively exploited (CISA KEV)Public exploitEPSS 69.5%
  1. Published14 Jul 2026
  2. Added to CISA KEV18 Aug 2026
  3. Remediation due21 Aug 2026
Actively exploited (CISA KEV)

Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.

Added to KEV: 18 Aug 2026Federal remediation due: 21 Aug 2026

Description

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Microsoft SharePoint Server2016 · 2019 · < 16.0.19725.20434

Remediation

Fixed in
Microsoft SharePoint Server≥ 16.0.19725.20434

References

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Frequently asked

Is CVE-2026-55040 being actively exploited?

Yes. CVE-2026-55040 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 18 Aug 2026.

How severe is CVE-2026-55040?

CVE-2026-55040 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 69.5% probability of exploitation.

Which products are affected by CVE-2026-55040?

Affected products include Microsoft SharePoint Server.

How do I fix CVE-2026-55040?

Upgrade affected software to a fixed version, for example Microsoft SharePoint Server 16.0.19725.20434 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-55040 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.