CVE-2026-55040
Act now ● On CISA KEV — actively exploited
Actively exploited — on the CISA KEV list.
CVSS base
9.1
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
EPSS — probability of exploitation (30 days)
50.6%
98.9th percentile
CISA KEV
Listed
Added 2026-08-18 · patch by 2026-08-21
Weakness / dates
CWE-1390
Published 2026-07-14 · modified 2026-08-19
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Affected
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040
- exploit https://github.com/sfewer-r7/CVE-2026-55040
- exploit 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/