CVE-2026-55040: listed in the CISA KEV catalog

CVE-2026-55040 · CVSS 9.1 CRITICAL · KEV 2026-08-18 · patch available

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

Is CVE-2026-55040 exploited?

• Listed in the CISA KEV catalog on 2026-08-18.
• Federal remediation due 2026-08-21.
• Past that date by 41 days.
• Public exploit code: none found in monitored sources.
• Public detection rules exist.

Which products and versions are affected?

• Microsoft · Microsoft SharePoint Enterprise Server 2016 · < 16.0.5561.1001
• Microsoft · Microsoft SharePoint Server 2019 · < 16.0.10417.20175
• Microsoft · Microsoft SharePoint Server Subscription Edition · < 16.0.19725.20434

Is there a patch?

• KB5002891
• KB5002883
• KB5002882

What PlainSec published about CVE-2026-55040

• CISA’s KEV Update Spans Four Live Exploits (2026-08-17)
• SharePoint JWT Flaw Is Being Exploited (2026-08-14)
• VulnCheck Chains SharePoint Bypass Into RCE (2026-08-11)

Primary sources

• NVD record
• CISA KEV catalog
• Microsoft KB5002891
• Microsoft KB5002883
• Microsoft KB5002882
• Nuclei template

What this record does not say

• No EPSS score.

KEV and EPSS are re-checked daily. Record last updated 2026-08-27.