CVE-2026-55040
Microsoft SharePoint Weak Authentication Vulnerability
Published Jul 14, 2026 · updated Aug 18, 2026 · 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
Timeline
Detection, updates, and resolution for this record.
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.
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
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.
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
Required action
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.
CISA due date Aug 21, 2026
Affected
- cpe microsoft/sharepoint serverversion unspecified
- cpe microsoft/sharepoint server2016
- cpe microsoft/sharepoint server2019
- vendor Microsoft SharePointversion unspecified
Sources
- CISA KEVCVE-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.orgCVE-2026-55040
Official CVE identifier
cve.org - FIRST EPSSCVE-2026-55040
30-day exploitation probability 69.5%
first.org - NIST NVDCVE-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 DatabaseCVE-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