CVE-2026-55040
CRITICALCVSS 3.1 · 9.1 · secure@microsoft.com
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
CISA KEV: known exploited
Added: 2026-08-18 · Due: 2026-08-21
Known ransomware use: Unknown
EPSS: 69.54% · Percentile: 99.4%
As of 2026-10-27
EPSS estimates exploitation probability over the next 30 days. KEV due dates apply to US federal civilian agencies. Confirm your affected versions in vendor advisories.
CWE: CWE-1390 · Published: 2026-07-14T18:18:15.413 · Modified: 2026-08-19T04:17:23.540
Sources: NIST NVD, CISA KEV, FIRST EPSS. NVD and EPSS cached up to 6 hours; KEV up to 12 hours.
References and fixes
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- https://github.com/sfewer-r7/CVE-2026-55040
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-55040
- https://www.rapid7.com/blog/post/ra-microsoft-sharepoint-jwt-token-authentication-bypass-cve-2026-55040/