Vulnerability · Published Oct 8, 2026 · Assigned by Go
CVE-2026-78663Double flow control refund on HTTP/2 server streams in net/http
Critical 9.1
In plain English
A critical-severity security flaw in net/http from Go standard library. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.6%top 50.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:8 | delve | 1.26.1-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:10 | go-toolset | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | go-toolset | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | go-toolset | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-bin | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-bin | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-bin | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-docs | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-docs | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-docs | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-misc | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-misc | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-misc | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-race | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-race | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-race | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-src | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-src | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-src | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| AlmaLinux:10 | golang-tests | 1.26.10-1.el10_2.alma.1 | ALSA-2026:86093 |
| AlmaLinux:8 | golang-tests | 1.26.10-1.module_el8.10.0+4307+6e4cbc60 | ALSA-2026:86203 |
| AlmaLinux:9 | golang-tests | 1.26.10-1.el9_8 | ALSA-2026:86196 |
| Alpine:v3.24 | docker | 29.9.0-r0 | ALPINE-CVE-2026-78663 |
| Alpine:v3.24 | go | 1.26.9-r0 | ALPINE-CVE-2026-78663 |
| Debian:12 | golang-1.19 | no fix listed | DEBIAN-CVE-2026-78663 |
| Debian:13 | golang-1.24 | no fix listed | DEBIAN-CVE-2026-78663 |
| Debian:14 | golang-1.26 | 1.26.9-1 | DEBIAN-CVE-2026-78663 |
| Debian:14 | golang-1.27 | 1.27.2-1 | DEBIAN-CVE-2026-78663 |
| Debian:12 | golang-golang-x-net | no fix listed | DEBIAN-CVE-2026-78663 |
| Debian:13 | golang-golang-x-net | no fix listed | DEBIAN-CVE-2026-78663 |
| Debian:14 | golang-golang-x-net | 1:0.60.0-1 | DEBIAN-CVE-2026-78663 |
| Go | golang.org/x/net | 0.60.0 | GO-2026-6612 |
| Go | stdlib | 1.26.9 | GO-2026-6612 |
| Go | stdlib | 1.27.2 | GO-2026-6612 |
| Ubuntu:22.04:LTS | adsys | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | adsys | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | adsys | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | adsys | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | containerd | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | containerd | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.17 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.18 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.20 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.21 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.21 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.22 | 1.22.2-2~22.04.4 | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.22 | 1.22.2-2~22.04.4 | USN-8935-1 |
| Ubuntu:24.04:LTS | golang-1.22 | 1.22.2-2ubuntu0.5 | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.22 | 1.22.2-2ubuntu0.5 | USN-8935-1 |
| Ubuntu:22.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | golang-1.23 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | golang-1.24 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | golang-1.25 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | golang-1.26 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | golang-1.26 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | golang-1.27 | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | golang-golang-x-net | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | golang-golang-x-net | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | golang-golang-x-net | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | google-guest-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | google-guest-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | google-guest-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | google-guest-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:22.04:LTS | google-osconfig-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:24.04:LTS | google-osconfig-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.04:LTS | google-osconfig-agent | no fix listed | UBUNTU-CVE-2026-78663 |
| Ubuntu:26.10 | google-osconfig-agent | no fix listed | UBUNTU-CVE-2026-78663 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Go standard library | net/http | 0 – before 1.26.9 |
| Go standard library | net/http/internal/http2 | 1.27.0-0 – before 1.27.2 |
| golang.org/x/net | golang.org/x/net/http2 | 0 – before 0.60.0 |
Weakness: CWE-675 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H