CVE-2026-40365Network attack vector

Authenticated code execution via unsafe deserialization

Published May 12, 2026 · Updated May 12, 2026

Deserialization of untrusted data in Microsoft SharePoint Server allows remote authenticated users to execute arbitrary code over a network. Microsoft has not disclosed the deserialization entry point, serialized object format, or code path that processes attacker-controlled data. Low-privileged SharePoint access is required; affected builds are Enterprise 2016 before 16.0.5552.1002, Server 2019 before 16.0.10417.20128, and Subscription Edition before 16.0.19725.20280.

CVSS severity8.8
High
EPSS probability0.96%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Deserialization of untrusted data in Microsoft SharePoint Server allows remote authenticated users to execute arbitrary code over a network. Microsoft has not disclosed the deserialization entry point, serialized object format, or code path that processes attacker-controlled data. Low-privileged SharePoint access is required; affected builds are Enterprise 2016 before 16.0.5552.1002, Server 2019 before 16.0.10417.20128, and Subscription Edition before 16.0.19725.20280.

The record

CVE
CVE-2026-40365
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Microsoft
Product
Microsoft SharePoint Enterprise Server 2016
Classifications
CWE-1220, CAPEC-1, CAPEC-180, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.0.0 <16.0.5552.1002

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft SharePoint Enterprise Server 2016version=16.0.0 <16.0.5552.1002
Microsoft · Microsoft SharePoint Server 2019version=16.0.0 <16.0.10417.20128
Microsoft · Microsoft SharePoint Server Subscription Editionversion=16.0.0 <16.0.19725.20280

Published CVSS scores

8.8Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1220Insufficient Granularity of Access Control
CAPEC-1Accessing Functionality Not Properly Constrained by ACLs
CAPEC-180Exploiting Incorrectly Configured Access Control Security Levels
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo