# CVE-2026-55040: Microsoft SharePoint Weak Authentication Vulnerability

- Exploited (CISA KEV): yes, added 2026-08-18
- Published: 2026-07-14
- CVSS: 9.1 CRITICAL (v3.1)
- EPSS: 69.5% (99th percentile)
- CWE: CWE-1390

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

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | No public claim | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | No public claim | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2026-09-16 | 64 |
| Akamai | No public source | — | — |
| OWASP CRS | No public claim | — | — |

### F5

- 2026-09-16 · new · rule 200013210
  > Added: signature 200013210 "JWT none algorithm (4)" (Authentication/Authorization Attacks, risk High), systems: System Independent, SharePoint. References: CVE-2023-29357, CVE-2026-55040.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2026-55040 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2026-55040