Vulnerability record

CVE-2026-58644

Microsoft SharePoint Deserialization of Untrusted Data Vulnerability

CriticalExploitation confirmedCISA KEV

What should I do?

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog: attackers are using it. If you run SharePoint, fix it now.

CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

US federal civilian agencies must remediate by Jul 19, 2026.

Patch status

Official fix available since Sep 29, 2026

Apply the vendor's update to every affected system. Check the fixed-in versions below where known.

Basis: NVD patch reference

Patch or advisory on msrc.microsoft.com (opens in a new tab)

Description

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

Source: NIST National Vulnerability Database. Official vulnerability data, reproduced as published.

Affected products

Products affected by this vulnerability, with versions and the source of each entry
Product	Vendor	Affected versions	Fixed in	Source
SharePoint	Microsoft	—	—	KEV
SharePoint Server	Microsoft	< 16.0.19725.20434; 2016; 2019	16.0.19725.20434	NVD

Sources: KEV = CISA Known Exploited Vulnerabilities catalog; NVD = NIST National Vulnerability Database.

Intelligence timeline

Developments from the last 30 days, newest first.

CVSS scoredUpdateKEVSep 29, 2026
CVE-2026-58644 scored CVSS 9.8: Microsoft SharePoint, Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
CISA lists this as exploited in the wild. Unpatched SharePoint systems are exposed to active attacks now.
Basis: NIST National Vulnerability Database
Patch releasedUpdateKEVSep 29, 2026
Patch released for CVE-2026-58644: Microsoft SharePoint, Microsoft SharePoint Deserialization of Untrusted Data Vulnerability
An official fix is now available for Microsoft SharePoint. This vulnerability is being exploited, so apply it promptly.
Basis: NVD patch reference

1 earlier event is available with a subscription. See plans.

Coverage

We have not published a story about this vulnerability yet.

References

msrc.microsoft.com https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58644
cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-ba…
nvd.nist.gov https://nvd.nist.gov/vuln/detail/CVE-2026-58644
cisa.gov https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-58644