CVE-2026-45659

Published May 22, 2026

Last updated a month ago

Exploit known CVSS high 8.8

Microsoft Office SharePoint

lms

Network

Zero-day

Server

Overview

AI description

Automated description summarized from trusted sources.

CVE-2026-45659 is a remote code execution (RCE) vulnerability found in Microsoft SharePoint Server, stemming from a deserialization of untrusted data issue. This flaw allows an authenticated attacker with low privileges, such as a Site Member, to execute arbitrary code on the server without requiring user interaction. The vulnerability affects SharePoint Server Subscription Edition, SharePoint Server 2019, and SharePoint Enterprise Server 2016. Despite Microsoft initially assessing the vulnerability as "less likely to be exploited," the U.S. Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2026-45659 to its Known Exploited Vulnerabilities (KEV) catalog in July 2026, confirming active exploitation in the wild. A patch for this vulnerability was included in the May 2026 security updates, though its details were inadvertently omitted from the initial release notes.

Description: Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
Source: secure@microsoft.com
NVD status: Analyzed
Products: sharepoint_server

Risk scores

CVSS 3.1

Type: Secondary
Base score: 8.8
Impact score: 5.9
Exploitability score: 2.8
Vector string: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Severity: HIGH

Known exploits

Data from CISA

Vulnerability name: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Exploit added on: Jul 1, 2026
Exploit action due: Jul 4, 2026
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.

Weaknesses

secure@microsoft.com: CWE-502

Hype score: Not currently trending

Configurations

[
  {
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:a:microsoft:sharepoint_server:*:*:*:*:subscription:*:*:*",
            "matchCriteriaId": "E9919927-DE08-4AE4-B9F6-2A83117EE14A",
            "versionEndExcluding": "16.0.19725.20280",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:microsoft:sharepoint_server:2016:*:*:*:enterprise:*:*:*",
            "matchCriteriaId": "F815EF1D-7B60-47BE-9AC2-2548F99F10E4",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*",
            "matchCriteriaId": "6122D014-5BF1-4AF4-8B4D-80205ED7785E",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ]
  }
]

References

Sources include official advisories and independent security research.