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CVE-2026-45659

Microsoft SharePoint Server Deserialization of Untrusted Data

8.8 HIGHActively exploited (CISA KEV)Used in ransomwareEPSS 2.70%
  1. Published22 May 2026
  2. Added to CISA KEV1 Jul 2026
  3. Remediation due4 Jul 2026
Actively exploited (CISA KEV)

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

Added to KEV: 1 Jul 2026Federal remediation due: 4 Jul 2026Used in ransomware

Description

Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.

CVSS 3.1 breakdown

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

Affected products

Microsoft SharePoint Server2016 · 2019 · < 16.0.19725.20280

Remediation

Fixed in
Microsoft SharePoint Server≥ 16.0.19725.20280

References

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Frequently asked

Is CVE-2026-45659 being actively exploited?

Yes. CVE-2026-45659 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 1 Jul 2026. It has been used in ransomware campaigns.

How severe is CVE-2026-45659?

CVE-2026-45659 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 2.70% probability of exploitation.

Which products are affected by CVE-2026-45659?

Affected products include Microsoft SharePoint Server.

How do I fix CVE-2026-45659?

Upgrade affected software to a fixed version, for example Microsoft SharePoint Server 16.0.19725.20280 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-45659 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.