Risk Letters

Exploited vulnerability

CVE-2026-55040

TLP:CLEAR

Microsoft SharePoint Weak Authentication Vulnerability

Microsoft SharePoint contains a weak authentication vulnerability which allows an unauthorized attacker to bypass a security feature over a network.

Facts

  • Vendor: Microsoft
  • Product: SharePoint
  • CVSS: 9.1
  • EPSS (probability of exploitation within 30 days): 69.5 %
  • On CISA's Known Exploited Vulnerabilities list since: 18 August 2026
  • First known exploitation: 18 August 2026
  • CISA's deadline for US federal agencies: 21 August 2026
  • Weakness: CWE-1390
  • First seen by Risk Letters: 25 August 2026

Members see which Nordic sectors the flaw hits, and what to do about it.

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Data: NVD (public domain), CISA KEV, FIRST EPSS, MITRE ATT&CK, AlienVault OTX. NVD