Authentication Bypass in Microsoft Office SharePoint
CVE-2026-55040

9.1CRITICAL

Key Information:

Vendor

Microsoft
Status
Microsoft Sharepoint Enterprise Server 2016
Microsoft Sharepoint Server 2019
Microsoft Sharepoint Server Subscription Edition
Vendor
CVE Published:
14 July 2026

Badges

🥇 Trended No. 1📈 Trended📈 Score: 21,100💰 Ransomware👾 Exploit Exists🟡 Public PoC🟣 EPSS 50%🦅 CISA Reported📰 News Worthy

What is CVE-2026-55040?

CVE-2026-55040 is a security vulnerability identified in Microsoft Office SharePoint, a platform widely used for collaboration, document management, and storage. This vulnerability arises from weak authentication mechanisms, which allow unauthorized attackers to bypass critical security features over a network. As a result, an attacker could gain unauthorized access to sensitive information or resources within SharePoint environments. Given the potential for such a breach, organizations relying on SharePoint for critical business processes may face significant risks, including data leakage and unauthorized actions within their systems.

Potential Impact of CVE-2026-55040

  1. Unauthorized Access: The vulnerability enables attackers to bypass authentication, directly leading to potential unauthorized access to sensitive documents and information stored within SharePoint. This access can facilitate data theft or manipulation.

  2. Data Breaches: With unauthorized access, attackers may exploit the vulnerabilities to exfiltrate confidential information, which could result in compliance violations, legal ramifications, and reputational damage for affected organizations.

  3. Operational Disruption: An attacker exploiting this vulnerability could disrupt business operations by altering or deleting important data, severely impacting productivity and leading to costly recovery efforts as organizations work to restore their systems and data integrity.

CISA has reported CVE-2026-55040

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-2026-55040 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 < 16.0.5561.1001

Microsoft SharePoint Server 2019 x64-based Systems 16.0.0 < 16.0.10417.20175

Microsoft SharePoint Server Subscription Edition x64-based Systems 16.0.0 < 16.0.19725.20434

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-2026-55040-Mass-Exploit
Created by maxprog-svg

News Articles

favicon imageAnalytics And Insight

Microsoft SharePoint Exploit Chain: Why the Latest RCE Flaw Matters

Microsoft SharePoint is under active attack via an exploit chain that combines authentication bypass and RCE flaws. Here’s what organizations need to know.

3 weeks ago

favicon imageOnmsft

Two SharePoint Flaws Give Hackers a Path to Remote Code Execution

Hackers are probing a Microsoft SharePoint exploit chain that combines CVE-2026-55040 and CVE-2026-63520 for potential remote code execution.

4 weeks ago

favicon imageBleepingComputer

Hackers target Microsoft SharePoint RCE chain with PoC exploit

Attackers are now targeting a chain of two Microsoft SharePoint vulnerabilities that can allow them to execute arbitrary code on unpatched servers, according to threat intelligence company Defused.

1 month ago

References

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

EPSS Score

50% chance of being exploited in the next 30 days.

CVSS V3.1

Score:
9.1
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • 🟡

    Public PoC available

  • 💰

    Used in Ransomware

  • 🦅

    CISA Reported

  • 🥇

    Vulnerability reached the number 1 worldwide trending spot

  • 📈

    Vulnerability started trending

  • 👾

    Exploit known to exist

  • 📰

    First article discovered by The Hacker News

  • Vulnerability published

  • Vulnerability Reserved

.