CVE-2026-78667 and is rated High severity with a CVSS score of 7.5. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.
What to do next
Remediation and response
Microsoft Security Response Center guidance
Vendor revision: Oct 17, 2026
Release Notes
CISA KEVNot listedBased on the latest collected catalog
EPSS0.4%Estimated 30-day exploitation probability
Ransomware useNot markedCISA KEV ransomware field
Threat actors0Source-linked actor relationships
Overview
What is CVE-2026-78667?
When parsing a Range header containing a large number of small ranges, FileServer(FS), ServeContent, and ServeFile(FS) can consume an excessive amount of CPU.