CVE-2026-78660 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 21, 2026
Vendor remediation details
Release Notes
Vendor-listed releases
10.25.1-10
1.7.0-2
1.12.15-15
8.7.11-10
0.5.1-10
2.3.7-1
1.62.0-9
1.32.0-10
0.14.0-19
2.27.0-16
0.24.2-34
2.102.0-2
3.10.182-6
2.14.1-22
0.0.10-11
1.8.4-4
1.15.0-7
4.0.2-12
1.9.5-23
0.12.0-12
1.7.0-6
0.8.2-6
1.14.4-14
3.7.0-9
1.31.0-35
19.0.4-15
CISA KEVNot listedBased on the latest collected catalog
EPSS0.3%Estimated 30-day exploitation probability
Ransomware useNot markedCISA KEV ransomware field
Threat actors0Source-linked actor relationships
Overview
What is CVE-2026-78660?
Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such headers to an HTTP/1 client when acting as a reverse proxy.
If the HTTP/1 client also does not behave strictly enough, this can result in response smuggling.