CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

CISA Known Exploited Vulnerabilities

Name

Microsoft SharePoint Weak Authentication Vulnerability

Vendor

Microsoft

Product

SharePoint

Added to the catalog

2026-08-18

Due date for US federal agencies

2026-08-21

Weaknesses

CWE-1390

Catalog version

2026.10.30

Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.

Required action (CISA)

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.

Ransomware use: CISA does not mark known use of this vulnerability in ransomware campaigns.

Links in CISA's notes

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
• https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
• https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
• https://nvd.nist.gov/vuln/detail/CVE-2026-55040

Read on 2026-11-02T23:39:54.475Z under licence cisa-kev-cc0@b0067899 from https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

NVD analysis

Status

Analyzed

Published

2026-07-14T18:18:15.413

Last modified

2026-08-19T04:17:23.540

Weaknesses

CWE-1390

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

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 (Patch, Vendor Advisory)
• https://github.com/sfewer-r7/CVE-2026-55040 (Exploit)
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040 (Exploit, Third Party Advisory)
• https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/ (US Government Resource)

This product uses the NVD API but is not endorsed or certified by the NVD.

Read on 2026-11-02T23:42:31.494Z under licence nvd-api-terms-of-use@ff2a5288 from https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-55040

CVE record

Title (CNA)

Microsoft SharePoint Server Security Feature Bypass Vulnerability

Assigner

microsoft

State

PUBLISHED

Published

2026-07-14T17:09:00.641Z

Updated

2026-11-01T17:36:32.366Z

Problem types

CWE-1390: Weak Authentication

References

• Microsoft SharePoint Server Security Feature Bypass Vulnerability

Read on 2026-11-03T02:20:35.161Z under licence cve-terms-of-use@81bfa2f3 from https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/55xxx/CVE-2026-55040.json

Defensive techniques (MITRE D3FEND)

D3FEND maps these defensive techniques to the weakness (CWE) that NVD lists for this CVE, through the digital artifacts the weakness affects. D3FEND does not say they stop this vulnerability.

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