Deserialization Vulnerability in Microsoft Office SharePoint
CVE-2026-45659

8.8HIGH

Key Information:

Vendor

Microsoft
Status
Microsoft Sharepoint Enterprise Server 2016
Microsoft Sharepoint Server 2019
Microsoft Sharepoint Server Subscription Edition
Vendor
CVE Published:
22 May 2026

Badges

📈 Trended📈 Score: 3,960💰 Ransomware👾 Exploit Exists🟡 Public PoC🦅 CISA Reported📰 News Worthy

What is CVE-2026-45659?

CVE-2026-45659 is a critical vulnerability affecting Microsoft Office SharePoint, a platform widely used for collaboration, document management, and storing business data. This vulnerability arises from a flaw in the deserialization process of untrusted data, which potentially allows an authorized attacker to execute arbitrary code over a network. If exploited, it can enable attackers to manipulate the application environment and gain unauthorized control over sensitive data and system resources. The risk is heightened due to SharePoint's integral role in organizational workflows and its common deployment in enterprise settings, making it a significant target for cyber threats.

Potential impact of CVE-2026-45659

  1. Unauthorized Code Execution: The most direct consequence of this vulnerability is the ability for attackers to execute malicious code without proper authorization. This could lead to the takeover of affected systems, creating opportunities to further compromise organizational networks.

  2. Data Breach Risks: With the exploitation of this vulnerability, attackers could gain access to sensitive information stored within SharePoint. This exposure could result in severe data breaches, jeopardizing confidential business data and potentially leading to regulatory penalties.

  3. Disruption of Business Operations: Successful exploitation may lead to significant operational disruptions. An attacker could manipulate SharePoint’s functionality or deploy ransomware, affecting user access and collaboration, ultimately impacting productivity and business continuity.

CISA has reported CVE-2026-45659

CISA provides regional cyber and physical services to support security and resilience across the United States. CISA monitor the most dangerious vulnerabilities and have identifed CVE-2026-45659 as being exploited but is not known by the CISA to be used in ransomware campaigns. This is subject to change at pace as recent news articles suggest the vulnerability is being used by ransomware groups.

The CISA's recommendation is: 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.

Affected Version(s)

Microsoft SharePoint Enterprise Server 2016 x64-based Systems 16.0.0 < 16.0.5552.1002

Microsoft SharePoint Server 2019 x64-based Systems 16.0.0 < 16.0.10417.20128

Microsoft SharePoint Server Subscription Edition x64-based Systems 16.0.0 < 16.0.19725.20280

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-45659
Created by HORKimhab

News Articles

favicon imageComputer World

CISA urges immediate SharePoint hardening as exploits mount

Three actively exploited SharePoint vulnerabilities have landed in the KEV catalog, with security experts warning that patching alone won’t prevent business disruption.

2 weeks ago

favicon imageBleepingComputer

CISA warns admins to patch actively exploited SharePoint flaws

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) warned Tuesday that attackers are actively exploiting three vulnerabilities to hack Internet-exposed on-premises SharePoint Server instances.

2 weeks ago

favicon imageTechtimes

July Patch RoguePlanet Tuesday Kills Windows Kerberos RC4 Rollback: Service Accounts Face No-Recovery Deadline

July 2026 Patch Tuesday permanently removes the Kerberos RC4 rollback registry key on July 14, leaving service accounts with RC4-only material unable to authenticate. Administrators must also verify

2 weeks ago

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE...
vendor-advisorypatch

EPSS Score

9% chance of being exploited in the next 30 days.

CVSS V3.1

Score:
8.8
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • 🦅

    CISA Reported

  • 💰

    Used in Ransomware

  • 📈

    Vulnerability started trending

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • 📰

    First article discovered by It Security News

  • Vulnerability published

  • Vulnerability Reserved

.