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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

Patch now

CVE-2026-55040 is in the CISA known-exploited catalog, due Aug 21, 2026. Confirm Microsoft SharePoint against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
Severity
Critical9.1
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
69.54%
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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

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

How to fix CVE-2026-55040

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2026-55040 is in the CISA known-exploited catalog, due Aug 21, 2026. Confirm Microsoft SharePoint against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with microsoft/sharepoint server 2016; microsoft/sharepoint server 2019. 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.

What should an analyst verify?

CWE-1390. EPSS 69.54%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

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

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.