CVE-2026-55040 KEV
9.1
CRITICAL · CVSS 3.1 · EPSS 17.5% (pctl 97)
Patch first
On CISA KEV — known exploited in the wild, due 2026-08-21.
Description
Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.
Scoring
| CVSS | 9.1 (CRITICAL, v3.1) |
|---|---|
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| EPSS | 17.54% — more likely to be exploited than 97% of all CVEs |
| Weakness | CWE-1390 |
| On CISA KEV | yes — remediate by 2026-08-21 |
| Public exploit | none known |
| Published | 2026-07-14 |
| Last modified | 2026-08-19 |
CISA KEV
| Name | Microsoft SharePoint Weak Authentication Vulnerability |
|---|---|
| Added | 2026-08-18 |
| Due | 2026-08-21 |
| Vendor / product | Microsoft / SharePoint |
| Ransomware use | none reported |
Affected (1)
| Vendor | Product |
|---|---|
| microsoft | sharepoint server |
References
- 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/
→ the Explorer · watch your stack · NVD