Exploited vulnerability CISA KEV
CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability
CVE-2026-55040 is a vulnerability in Microsoft SharePoint that CISA added to its Known Exploited Vulnerabilities catalog on August 18, 2026, meaning there is evidence it is being exploited. US federal civilian agencies must complete the required action by August 21, 2026.
CVE-2026-55040 is a vulnerability in Microsoft SharePoint that CISA added to its Known Exploited Vulnerabilities catalog on August 18, 2026, meaning there is evidence it is being exploited. US federal civilian agencies must complete the required action by August 21, 2026.
- CVE ID
- CVE-2026-55040
- Vendor / project
- Microsoft
- Product
- SharePoint
- Added to KEV
- Due date
- Days to remediate
- 3
- Known ransomware use
- Unknown
- Weakness
- CWE-1390
CISA description #
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
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.
Notes and references #
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: 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
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