Actively exploited
Listed in CISA’s Known Exploited Vulnerabilities catalog since August 18, 2026.
CVE-2026-55040
Microsoft SharePoint Weak Authentication Vulnerability
Added to KEV August 18, 2026
Alert details
- Source feed
- CISA KEV
- CVE ID
- CVE-2026-55040
- CWE
- CWE-1390
- Affected products
- SharePoint · Microsoft SharePoint · Microsoft
What happened
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
What it means for your business
Microsoft SharePoint is listed in CISA's Known Exploited Vulnerabilities catalog (CVE-2026-55040). Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network. CISA remediation due date: 2026-08-21. If you need help checking exposure, call (864) 335-9223.
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: August 21, 2026
Sources
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