CVE intelligence

CVE-2026-78663

Vulnerability intelligence

Published Oct 8, 2026Sources checked Oct 21, 2026

9.1CRITICALCVSS out of 10

What this means

Review the available evidence

CVE-2026-78663 and is rated Critical severity with a CVSS score of 9.1. 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

1.12.15-15
0.5.1-10
1.62.0-9
2.7.5-22
2.14.1-22
0.0.10-11
1.8.4-4
0.12.0-12
1.7.0-6
0.8.2-6

CISA KEVNot listedBased on the latest collected catalog

EPSS0.6%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-78663?

The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection).

Total buffered data is still limited by the concurrent stream limit and stream-level flow control.

Source: NVD