Microsoft SharePoint Weak Authentication
What to do
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 deadline 2026-08-21 · passed 20 days ago · applies to US federal civilian agencies; used elsewhere as a reference SLA
What happened
Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.
Who is affected
Microsoft SharePoint. Affected version ranges are listed in the vendor advisory and the NVD entry linked under Sources.
Weakness class: CWE-1390.
Timeline
- Added to CISA KEVExploitation in the wild confirmed by CISA
- CISA remediation deadlinepassed 20 days ago
Sources
- NVD entry for CVE-2026-55040 nvd.nist.gov/vuln/detail/CVE-2026-55040
- CISA Known Exploited Vulnerabilities catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
- msrc.microsoft.com msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- cisa.gov www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- cisa.gov www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- nvd.nist.gov nvd.nist.gov/vuln/detail/CVE-2026-55040