What is the CVSS score of CVE-2026-55040?

CVE-2026-55040 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.7%.

Which versions of Microsoft SharePoint are affected by CVE-2026-55040?

Microsoft SharePoint (2016, 2019, Subscription Edition) contains a critical security bypass enabling unauthenticated remote attackers to compromise data confidentiality and integrity without user…. A patch is available.

Is there a public PoC exploit available for CVE-2026-55040?

Yes, a public proof-of-concept exploit is available for CVE-2026-55040. Prioritise patching immediately. EPSS: 0.7%.

How to fix or mitigate CVE-2026-55040?

Within 24 hours, inventory all SharePoint 2016, Server 2019, and Subscription Edition deployments with priority mapping for internet-facing systems; confirm patch availability from Microsoft advisory. Within 7 days, apply the Microsoft-released patch to all affected SharePoint instances across all environments. Within 30 days, conduct post-patch verification through automated scanning, validate completeness across the estate, and implement monitoring for exploitation attempts targeting CVE-2026-55040.

Microsoft SharePoint CVE-2026-55040

EUVD-2026-44211 CRITICAL

Weak Authentication (CWE-1390)

2026-07-14 microsoft

GHSA-grxw-7cvc-96rv

Authentication Bypass Microsoft Microsoft Sharepoint Enterprise Server 2016 Microsoft Sharepoint Server 2019 Microsoft Sharepoint Server Subscription Edition

9.1

CVSS 3.1 · Vendor: microsoft

Temporal: 7.9

Severity by source

Vendor (microsoft) PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

ENISA EUVD

CRITICAL

qualitative

CIRCL (temporal)

7.9 HIGH

cvss

vuln.today AI

9.1 CRITICAL

Authentication bypass reachable over the network with no credentials or interaction gives AV:N/AC:L/PR:N/UI:N; it exposes and alters protected data (C:H/I:H) but does not affect availability (A:N).

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

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Added to CISA KEV

Aug 18, 2026 - 17:48 CISA

Analysis Generated

Jul 14, 2026 - 19:27 vuln.today

CVE Published

Jul 14, 2026 - 17:09 cve.org

CRITICAL 9.1

DescriptionCVE.org

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

Articles & Coverage 1

POC CVE-2026-55040: Rapid7 PoC Exploits Microsoft SharePoint JWT Token Forgery to Bypass Authentication Aug 10, 2026

AnalysisAI

Security feature bypass in Microsoft SharePoint (Enterprise Server 2016, Server 2019, and Server Subscription Edition) lets a network-based, unauthenticated attacker defeat a weak-authentication protection mechanism (CWE-1390) to gain high-impact access to confidentiality and integrity. Rated CVSS 9.1 with no attacker privileges or user interaction required, this is a serious pre-authentication issue in a widely deployed collaboration platform. Microsoft has published a fix, and there is no public exploit identified at time of analysis.

Technical ContextAI

SharePoint is Microsoft's enterprise web-based collaboration and document-management platform, typically deployed on-premises on Windows Server with IIS front-ends and SQL Server back-ends. The root cause is CWE-1390 (Weak Authentication), meaning the affected authentication or security-feature-enforcement logic can be circumvented rather than correctly validated. Based on the CPE data, the flaw affects the on-premises server family - SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition - where the vulnerable code path is reachable over the network, allowing an attacker to bypass an intended security control without presenting valid credentials.

RemediationAI

Patch available per vendor advisory - apply the Microsoft security update for CVE-2026-55040 to all affected SharePoint farms (Enterprise Server 2016, Server 2019, and Subscription Edition) via https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040, following the standard SharePoint patching sequence of installing the update on every server in the farm and then running the SharePoint Products Configuration Wizard (PSConfig) to complete the upgrade. The exact fixed build number is not included in the provided data, so obtain it from the MSRC page. Until patching is complete, reduce exposure by restricting network reachability of the SharePoint web front-ends - do not expose on-premises SharePoint directly to the internet; place it behind a VPN or reverse proxy/WAF and limit inbound access to trusted networks (trade-off: this may block legitimate remote or extranet users) - and increase monitoring of authentication and access logs for anomalous requests to the affected endpoints.