CVE-2026-40365: Microsoft SharePoint Server Remote Code Execution Vulnerability
CVE-2026-40365 is a remote code execution vulnerability in Microsoft SharePoint Server, rated Critical by Microsoft, with a CVSS 3.1 base score of 8.8 (High). An attacker can exploit it remotely over the network, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as less likely. The EPSS model estimates a 0.96% probability of exploitation activity in the next 30 days, higher than 62% of all scored vulnerabilities. Microsoft released the fix on 12 May 2026 in the May 2026 Patch Tuesday, delivered through 3 security updates (KB5002868, KB5002870, KB5002863). It affects 3 products in 1 product family (Microsoft Office).
Key facts
- CVE ID
- CVE-2026-40365
- Severity
- High CVSS 8.8
- Microsoft severity
- Critical
- Impact
- Remote Code Execution
- Exploited in the wild
- No
- Publicly disclosed
- No
- Exploitation likelihood
- Less Likely
- Weakness
- CWE-1220
- EPSS
- 0.96% (percentile 62%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- May 2026 Patch Tuesday
- Product families
- Microsoft Office
CVSS score and vector
Microsoft scores CVE-2026-40365 at 8.8 (temporal 7.7) using CVSS 3.1. Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
| Metric | Value |
|---|---|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | Low |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | High |
| Integrity impact | High |
| Availability impact | High |
| Exploit code maturity | Unproven |
| Remediation level | Official fix |
| Report confidence | Confirmed |
Description
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
Frequently asked questions (Microsoft)
According to the CVSS metric, privileges required is low (PR:L). What does that mean for this vulnerability?
Any authenticated attacker could trigger this vulnerability. It does not require admin or other elevated privileges.
How could an attacker exploit the vulnerability?
In a network-based attack, an authenticated attacker, as at least a Site Owner, could write arbitrary code to inject and execute code remotely on the SharePoint Server.
I am running SharePoint Server 2016. Do the updates for SharePoint Enterprise Server 2016 also apply to the version I am running?
Yes. The same KB number applies to both SharePoint Server 2016 and SharePoint Enterprise Server 2016. Customers running either version should install the security update to be protected from this vulnerability.
Affected products (3)
Microsoft Office
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| Microsoft SharePoint Enterprise Server 2016 | KB5002868 | Security Update | 16.0.5552.1002 | Maybe |
| Microsoft SharePoint Server 2019 | KB5002870 | Security Update | 16.0.10417.20128 | Maybe |
| Microsoft SharePoint Server Subscription Edition | KB5002863 | Security Update | 16.0.19725.20280 | Maybe |
Security updates (3)
NIST NVD data
- NVD status
- Modified
- NVD CVSS
- 8.8 (HIGH)
- NVD weakness
- CWE-1220
- Published to NVD
- NVD last modified
Affected configurations (CPE)
| Product | Vulnerable versions |
|---|---|
| sharepoint server | before 16.0.19725.20280 |
| sharepoint server 2016 | all listed versions |
| sharepoint server 2019 | all listed versions |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40365 (Vendor Advisory)
Acknowledgments
- f7d8c52bec79e42795cf15888b85cbad
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. |