---
title: "CVE-2026-78663: HTTP/2 Server - Denial of Service"
description: "HTTP/2 server contains a flow control bypass caused by double refunding connection-level flow control for the same data, letting malicious clients bypass connection-level flow control limits, exploit requires malicious client to reset streams."
url: https://panop.io/threat-heartbeat/CVE-2026-78663/
---

# CVE-2026-78663 HTTP/2 Server - Denial of Service

HTTP/2 server contains a flow control bypass caused by double refunding connection-level flow control for the same data, letting malicious clients bypass connection-level flow control limits, exploit requires malicious client to reset streams.

CVSS base score 9.1 /10

Critical

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.57% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-78663)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Published

8 October 2026

Updated

15 October 2026

Weakness

[CWE-675](https://cwe.mitre.org/data/definitions/675.html)

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-78663](https://nvd.nist.gov/vuln/detail/CVE-2026-78663)
- [https://go.dev/cl/847187](https://go.dev/cl/847187)
- [https://go.dev/cl/847310](https://go.dev/cl/847310)
- [https://go.dev/issue/81743](https://go.dev/issue/81743)
- [https://groups.google.com/g/golang-announce/c/U2fTuyDJznI](https://groups.google.com/g/golang-announce/c/U2fTuyDJznI)
- [https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs](https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs)
- [https://pkg.go.dev/vuln/GO-2026-6612](https://pkg.go.dev/vuln/GO-2026-6612)

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- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
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