Microsoft SharePoint Weak Authentication Vulnerability

CRITICAL 9.1EXPLOITED (CISA KEV)CVE-2026-55040 · Published 14/07/2026 · updated 19/08/2026

Microsoft SharePoint Weak Authentication Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 18/08/2026. Patch affected systems as an emergency.

Package	Affected versions	Patched versions
sharepoint server microsoft	`= 2016= 2019< 16.0.19725.20434`	`16.0.19725.20434`

Description

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040 · Patch
sfewer-r7/CVE-2026-55040 · Exploit
cisa.gov/known-exploited-vulnerabilities-catalog · Exploit
rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040 · US Government Resource
CISA KEV · CVE-2026-55040

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