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Vulnerabilities

Vulnerability · CVE-2026-55040

Microsoft SharePoint Weak Authentication Vulnerability

Published Jul 14, 2026 · catalog updated Aug 18, 2026 · Microsoft SharePoint

Severity
Critical9.1
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
69.5%
Remediation
Remediation guidance
Affected products
cpe microsoft/sharepoint server · vendor Microsoft SharePoint

Overview Rapid7 Labs conducted a zero-day research project against Microsoft SharePoint, resulting in the discovery of two new vulnerabilities that, when chained together, achieve unauthenticated remote code execution (RCE) against a vulnerable SharePoint server. Today, both Rapid7 and Microsoft are disclosing the second vulnerability in this chain, the RCE vulnerability CVE-2026-63520. The first vulnerability in the chain, CVE-2026-55040, was disclosed by Rapid7 and Microsoft last month. Our full disclosure timeline for the exploit chain can be seen below in Figure 1. Figure 1: The road to di

Technical analysis

Mechanism and impact are interpreted from ingested advisories — not independent exploit research.

  • CWE classification

  • Prerequisites and impact

    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.

How to fix CVE-2026-55040

What to do

Three reads of the same public record: the decision, the versions on file, and the signals. Confirm the vendor advisory before you patch. This page does not publish exploit steps.

Executive

Treat this as an active risk. CVE-2026-55040 is a critical issue in Microsoft SharePoint (CVSS 9.1). CISA lists it as known exploited since Aug 12, 2026. Next step: 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.

System administrator

Check whether Microsoft SharePoint is installed. Ranges on record: microsoft/sharepoint server; microsoft/sharepoint server (2016); microsoft/sharepoint server (2019); Microsoft SharePoint. 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.

Security analyst

CVSS 9.1. EPSS 69.5%. CISA lists it as known exploited since Aug 12, 2026. Weaknesses: CWE-1390. Sources: cisa_kev, cve_org, epss, nvd. Exploit links, when listed below, point at the original publisher.

Related intelligence

  • Exploitation evidence

    Confirmed in CISA KEV since Aug 12, 2026. Listed in CISA KEV and VulnCheck KEV.

  • Safe detection guidance

    Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 14, 2026 · Catalog

    Detected

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

  2. Aug 18, 2026 · CISA KEV

    Known exploited

    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

  3. Aug 18, 2026 · Catalog

    Updated

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

  4. Aug 21, 2026 · CISA KEV

    Remediation due

    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

Affected versions

Enter an installed version to get a verified affected / not-affected result against the ranges below.

  • cpe microsoft/sharepoint serverversion unspecified
  • cpe microsoft/sharepoint server2016
  • cpe microsoft/sharepoint server2019
  • vendor Microsoft SharePointversion unspecified

Sources

  • CISA KEVConfirmed exploitationCVE-2026-55040

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

    cisa.gov
  • CVE.orgVulnerability recordCVE-2026-55040

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-55040

    30-day exploitation probability 69.5%

    first.org
  • NIST NVDVulnerability recordCVE-2026-55040

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

    nvd.nist.gov
  • Rapid7 Vulnerability DatabaseResearchCVE-2026-55040

    Overview Rapid7 Labs conducted a zero-day research project against Microsoft SharePoint, resulting in the discovery of two new vulnerabilities that, when chained together, achieve unauthenticated remote code execution (RCE) against a vulnerable SharePoint server. Today, both Rapid7 and Microsoft are disclosing the second vulnerability in this chain, the RCE vulnerability CVE-2026-63520. The first

    rapid7.com
  • VulnCheck KEVConfirmed exploitationCVE-2026-55040

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

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.