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CVE-2026-20959: Microsoft SharePoint Server Spoofing Vulnerability

• Severity: medium (CVSS 5.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 7.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-01-13 · updated 2026-07-30
• Weakness: CWE-79

Description

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.

Affected products

• Microsoft SharePoint Server: before 16.0.19127.20442; 2016, 2019 — fixed in 16.0.19127.20442
• Microsoft SharePoint Server Subscription Edition: from 16.0.0 before 16.0.19127.20442 — fixed in 16.0.19127.20442
• Microsoft Sharepoint Enterprise Server 2016: from 16.0.0 before 16.0.5535.1001 — fixed in 16.0.5535.1001
• Microsoft SharePoint Server: from 16.0.0 before 16.0.10417.20083 — fixed in 16.0.10417.20083

How to fix

Upgrade to a fixed version: Microsoft SharePoint Server 16.0.19127.20442; Microsoft SharePoint Server Subscription Edition 16.0.19127.20442; Microsoft Sharepoint Enterprise Server 2016 16.0.5535.1001; Microsoft SharePoint Server 16.0.10417.20083. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20959

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