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Fencer Vulns
high 7.5

CVE-2026-56866 json

HTTP/1 client connection desynchronization after CONNECT rejection in net/http

published 2026-10-08 31 d ago modified 2026-10-16 23 d ago also BIT-golang-2026-56866 , EUVD-2026-95421 , GO-2026-6605

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits
0
none known

Summary

When http.Transport sends an HTTP/1 CONNECT request with a non-empty Request.Body, it writes the body directly to the connection without framing after the request headers. If the server rejects the CONNECT request with a non-2xx keep-alive response, Transport returns the connection to the idle pool. Because CONNECT requests do not have a request body, the server may interpret the trailing body bytes as a subsequent pipelined HTTP/1.1 request on the connection, leaving the pooled connection desynchronized and causing the next caller that reuses it to read the response to the injected request. In reverse proxies (including httputil.ReverseProxy) that forward CONNECT requests through a shared Transport, this can lead to cross-user response poisoning.

Patch / fix

  • bitnami golang 1.26.9, 1.27.2
  • go stdlib 1.26.9, 1.27.2
  • Go standard library net/http 1.26.9, 1.27.2
  • Go standard library net/http/httputil 1.26.9, 1.27.2
  • golang-1.26 Debian 14 1.26.9-1
  • golang-1.27 Debian 14 1.27.2-1

debian advisories DEBIAN-CVE-2026-56866

  • golang-1.22 Ubuntu 22.04 LTS 1.22.2-2~22.04.4
  • golang-1.22 Ubuntu 24.04 LTS 1.22.2-2ubuntu0.5

ubuntu advisories UBUNTU-CVE-2026-56866

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • go1.26-openssl SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 1.26.10-150000.1.21.2
  • go1.26-openssl SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Development Tools 15 SP7 1.26.10-150600.13.18.1
  • go1.26 SLES for SAP applications 16.0, SLES 16.0 1.26.9-160000.1.1
  • go1.27 SLES for SAP applications 16.0, SLES 16.0 1.27.2-160000.1.1
  • go1.26 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 1.26.9-150000.1.33.1
  • go1.27 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 1.27.2-150000.1.12.1

suse advisories SUSE-SU-2026:4867-1SUSE-SU-2026:4866-1SUSE-SU-2026:24239-1SUSE-SU-2026:24237-1SUSE-SU-2026:4629-1SUSE-SU-2026:4625-1

  • go1.26 openSUSE Leap 16.0 1.26.9-160000.1.1
  • go1.27 openSUSE Leap 16.0 1.27.2-160000.1.1
  • rclone openSUSE Tumbleweed 1.75.2-1.1
  • go1.27 openSUSE Tumbleweed 1.27.2-1.1
  • go1.26 openSUSE Tumbleweed 1.26.9-1.1

opensuse advisories openSUSE-SU-2026:22095-1openSUSE-SU-2026:22093-1openSUSE-SU-2026:12112-1openSUSE-SU-2026:12101-1openSUSE-SU-2026:12093-1

  • golang AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • go-toolset AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang-bin AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang-src AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang-misc AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang-race AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang-tests AlmaLinux 10 1.26.10-1.el10_2.alma.1
  • golang AlmaLinux 9 1.26.10-1.el9_8

almalinux advisories ALSA-2026:86093ALSA-2026:86196ALSA-2026:86203

  • go Alpine 3.24 1.26.9-r0

alpine advisories ALPINE-CVE-2026-56866

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-56866 updated cvss 6.5

net/http: golang: golang: Cross-user response poisoning via desynchronized HTTP CONNECT connections

  • Red Hat OpenShift Developer Tools and Services helm 3.22.0-90.el9
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat OpenShift Pipelines openshift-pipelines-client 1.15.3-11580.el8 Red Hat OpenShift Serverless kn-workflow-plugin 1.38.1-1.el9, openshift-serverless-clients 1.17.0-4.el9 Red Hat OpenShift Service Mesh 3 istio-proxy-selinux, istio-proxy 1.30.5-1.el9, openshift-golang-builder-container
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Ansible Automation Platform 2 receptor 1.6.8-1.el9ap, automation-gateway-proxy 2.6.17-3.el9ap, automation-gateway-proxy-openssl30 2.6.6-2.el9ap, automation-gateway-proxy-openssl32 2.6.6-2.el9ap
    affected: workaround, no fix available, no fix planned “Out of support scope”
  • Red Hat Ceph Storage 7 thrift Red Hat Ceph Storage 8 thrift, thrift-qt, perl-thrift, thrift-glib, python3-thrift Red Hat Ceph Storage 9 thrift, libarrow, parquet-libs Red Hat Certification Program for Red Hat Enterprise Linux 9 redhat-certification-cnf 9.0-20240522.1.el9, redhat-certification-preflight 9.42-20261005.el10 Red Hat Enterprise Linux 7 rhc, host-metering, rhc-worker-script, rhc 0.3.13-1.el10_3, host-metering-selinux, compat-sap-c++-11 11.1.1-6.el7_9 Red Hat Enterprise Linux 8 rhc, crun, runc, conmon, podman, skopeo, +43 more
    +6 more products
    Red Hat Enterprise Linux 9 conmon, conmon 2.1.12-4.el10, oci-delta 0.3.0-1.el10 Red Hat Enterprise Linux 10 conmon 2.1.12-4.el10, oci-delta 0.3.0-1.el10 Red Hat Enterprise Linux AI (RHEL AI) 3 golang 1.25.1-1.el9 Red Hat OpenShift Container Platform 4 cri-o, butane, conmon, podman, skopeo, toolbox, +63 more Red Hat OpenShift Container Platform 5 cri-o, conmon-rs, cri-tools, openshift, microshift, kata-containers, +6 more Red Hat OpenShift on AWS rosa 1.2.64-b2f7c89.el8
    affected: workaround, no fix available “Fix deferred”
  • Red Hat OpenShift Virtualization 4 openshift-golang-builder-container
    affected: workaround, no fix available
  • Red Hat OpenStack Platform 16.2 etcd, golang-github-infrawatch-apputils 0.5-3.git4ffa970.el8ost Red Hat OpenStack Platform 17.1 etcd, golang-uber-multierr, collectd-libpod-stats, golang-uber-atomic 1.5.1-1.el8ost.1, golang-github-infrawatch-apputils 0.5-3.git4ffa970.el8ost
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat OpenStack Platform 18.0 etcd, golang-github-openstack-k8s-operators-os-diff 0.1.1-18.0.20260602234717.a95ae05.el9ost Red Hat Satellite 6 yggdrasil-worker-forwarder 0.1.0-2.1.el9sat
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Service Interconnect 1 skupper-cli 1.8.8-1.el9
    affected: workaround, no fix planned “Out of support scope”
show 4 more
  • Red Hat Service Interconnect 2 skupper-cli 1.8.8-1.el9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat streams for Apache Kafka 2 golang-github-danielqsj-kafka_exporter 1.9.0-12.el9
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat streams for Apache Kafka 3 golang-github-danielqsj-kafka_exporter 1.9.0-12.el9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Ansible Automation Orchestrator 2026 ansible-automation-platform/automation-orchestrator-rhel9-operator Red Hat Assisted Installer for Red Hat OpenShift Container Platform 2 rhai/assisted-installer-rhel9 Red Hat AWS Load Balancer Operator albo/aws-load-balancer-rhel8-operator Red Hat Builds for Red Hat OpenShift openshift-builds/openshift-builds-waiters-rhel9, openshift-builds/openshift-builds-waiters-rhel10 Red Hat cert-manager Operator for Red Hat OpenShift cert-manager/jetstack-cert-manager-rhel9 Red Hat Compliance Operator compliance/openshift-compliance-operator-bundle
    +8 more products
    Red Hat Confidential Compute Attestation build-of-trustee/trustee-rhel9-operator Red Hat Cost Management Metrics Operator costmanagement/costmanagement-metrics-rhel9-operator Red Hat Cost Management On Premise costmanagement/costmanagement-ingress-rhel9 Red Hat Cryostat 4 cryostat/cryostat-storage-rhel9 Red Hat Custom Metric Autoscaler operator for Red Hat Openshift custom-metrics-autoscaler/custom-metrics-autoscaler-rhel9 Red Hat Deployment Validation Operator dvo/deployment-validation-rhel8-operator Red Hat DPU kit for NVIDIA dpu-kit-for-nvidia/dpf-hcp-provisioner-rhel10-operator Red Hat Exploit Intelligence exploit-intelligence/exploit-intelligence-operator-controller-rhel9
    under investigation

65 more under investigation, 18 more fixed, 6 more not affected in the full advisory

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
30 d ago

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
bitnami golang
<1.26.9
>=1.27.0-0, <1.27.2
1.26.9
1.27.2
go stdlib
<1.26.9
>=1.27.0-0, <1.27.2
1.26.9
1.27.2

Affected products

  • Go standard library net/http
  • Go standard library net/http/httputil

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.