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Fencer Vulns
high 7.5

CVE-2026-56855 json

Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh

published 2026-09-02 2 mo ago modified 2026-09-24 46 d ago also EUVD-2026-70267 , GO-2026-6355

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking.

Patch / fix

  • go golang.org/x/crypto 0.56.0
  • golang.org/x/crypto golang.org/x/crypto/ssh 0.56.0
  • golang-go.crypto Debian 14 1:0.56.0-1

debian advisories DEBIAN-CVE-2026-56855

  • buildah RHEL 9 2:1.43.3-2.el9_8
  • buildah-tests RHEL 9 2:1.43.3-2.el9_8

red hat advisories RHSA-2026:70640

  • helm Linux Micro 6.1 4.3.0-slfo.1.1_1.1
  • terraform-provider-aws SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 3.11.0-150200.6.29.2
  • terraform-provider-tls SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 3.0.0-150200.5.26.2
  • terraform-provider-helm SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 2.9.0-150200.6.34.2
  • terraform-provider-null SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 3.0.0-150200.6.32.2
  • terraform-provider-local SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 2.0.0-150200.6.30.2
  • terraform-provider-google SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 3.43.0-150200.6.23.2
  • terraform-provider-random SLE Module for Public Cloud 15 SP5, SLE Module for Public Cloud 15 SP4 3.0.0-150200.6.26.2

suse advisories SUSE-SU-2026:24282-1SUSE-SU-2026:4628-1SUSE-SU-2026:24213-1SUSE-SU-2026:24148-1SUSE-SU-2026:4408-1SUSE-SU-2026:23973-1

  • zk openSUSE Tumbleweed 0.15.7-1.1
  • cosign openSUSE Leap 16.0 3.1.3-160000.1.1
  • alloy openSUSE Leap 16.0 1.19.2-160000.1.1
  • helm openSUSE Leap 16.0 4.3.0-160000.1.1
  • grafana openSUSE Tumbleweed 12.4.11-1.1
  • rclone openSUSE Leap 16.0 1.75.1-bp160.1.1
  • cosign openSUSE Tumbleweed 3.1.3-1.1
  • cloudflared openSUSE Leap 16.0 2026.9.1-bp160.1.1

opensuse advisories openSUSE-SU-2026:12258-1openSUSE-SU-2026:22064-1openSUSE-SU-2026:22032-1openSUSE-SU-2026:21983-1openSUSE-SU-2026:11920-1openSUSE-SU-2026:21999-1

  • buildah AlmaLinux 9 2:1.43.4-2.el9_8
  • buildah-tests AlmaLinux 9 2:1.43.4-2.el9_8
  • buildah AlmaLinux 9 2:1.43.3-2.el9_8
  • buildah-tests AlmaLinux 9 2:1.43.3-2.el9_8

almalinux advisories ALSA-2026:90424ALSA-2026:70640

  • buildah Rocky Linux 9 2:1.43.4-2.el9_8
  • buildah Rocky Linux 9 2:1.43.3-2.el9_8

rocky linux advisories RLSA-2026:90424RLSA-2026:70640

  • cert-manager Azure Linux 3.0 1.12.15-14
  • cf-cli Azure Linux 3.0 8.7.11-9
  • docker-buildx Azure Linux 3.0 0.14.0-17
  • docker-compose Azure Linux 3.0 2.27.0-14
  • gh Azure Linux 3.0 2.101.0-1
  • kubernetes Azure Linux 3.0 1.30.10-30
  • kubevirt Azure Linux 3.0 1.8.4-2
  • moby-engine Azure Linux 3.0 25.0.18-1

azure linux advisories AZL-99159AZL-99168AZL-99198AZL-99210AZL-99222AZL-99255

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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-2026-56855 updated cvss 5.3

golang.org/x/crypto/ssh: golang.org/x/crypto/ssh: Denial of Service via crafted messages

  • Red Hat Assisted Installer for Red Hat OpenShift Container Platform 2 assisted/agent-preinstall-image-builder-rhel9 Red Hat Builds for Red Hat OpenShift openshift-builds/openshift-builds-waiters-rhel9, openshift-builds/openshift-builds-webhook-rhel9, openshift-builds/openshift-builds-waiters-rhel10, openshift-builds/openshift-builds-webhook-rhel10, openshift-builds/openshift-builds-controller-rhel9, openshift-builds/openshift-builds-git-cloner-rhel9, +6 more Red Hat Confidential Compute Attestation openshift-sandboxed-containers/osc-rhel9-operator, openshift-sandboxed-containers/osc-podvm-payload-rhel9, openshift-sandboxed-containers/osc-cloud-api-adaptor-rhel9 Red Hat Cryostat 4 cryostat/cryostat-storage-rhel9 Red Hat External Secrets Operator for Red Hat OpenShift external-secrets-operator/external-secrets-rhel9 Red Hat Multicluster Engine for Kubernetes multicluster-engine/assisted-service-8-rhel8, multicluster-engine/assisted-service-9-rhel9, multicluster-engine/azure-service-operator-rhel9, multicluster-engine/assisted-installer-agent-rhel9, multicluster-engine/hypershift-addon-rhel9-operator, multicluster-engine/cluster-api-provider-azure-rhel9, +2 more
    +29 more products
    Red Hat OpenShift API for Data Protection oadp/oadp-velero-rhel9, oadp/oadp-mustgather-rhel9, oadp/oadp-velero-restic-restore-helper-rhel9 Red Hat OpenShift Pipelines openshift-pipelines-client 1.15.3-11580.el8 Red Hat OpenShift Serverless openshift-serverless-clients 1.17.0-4.el9, openshift-serverless-1/kn-plugin-func-func-util-rhel9 Red Hat Advanced Cluster Management for Kubernetes 2 flightctl-agent, flightctl-selinux, rhacm2/volsync-rhel9, flightctl 0.5.1-2.el8fc, rhacm2/acm-must-gather-rhel9, rhacm2/multicluster-operators-subscription-rhel9 Red Hat Advanced Cluster Security 4 advanced-cluster-security/rhacs-main-rhel8, advanced-cluster-security/rhacs-main-rhel9, advanced-cluster-security/rhacs-roxctl-rhel8, advanced-cluster-security/rhacs-roxctl-rhel9, advanced-cluster-security/rhacs-scanner-rhel8, advanced-cluster-security/rhacs-scanner-rhel9, +7 more Red Hat Ceph Storage 8 rhceph/grafana-rhel9 Red Hat Ceph Storage 9 rhceph/alloy-rhel10, rhceph/grafana-rhel10 Red Hat Edge Manager 1 flightctl 0.5.1-2.el8fc, rhem/flightctl-api-rhel9, rhem/flightctl-api-rhel10, rhem/flightctl-worker-rhel9, rhem/flightctl-worker-rhel10, rhem/flightctl-db-setup-rhel9, +19 more Red Hat Enterprise Linux 8 podman, buildah, podman-tests, buildah-tests, podman-docker, podman-remote, +4 more Red Hat Enterprise Linux 9 podman, podman-tests, podman-docker, podman-remote, podman-gvproxy, podman-plugins, +5 more Red Hat Enterprise Linux 10 grafana 12.4.3-2.el10, buildah 1.39.9-1.el10_0, podman 5.4.0-15.el10_0.2, gvisor-tap-vsock 0.8.7-1.el10 Red Hat OpenShift AI (RHOAI) rhoai/odh-trainer-rhel9, rhoai/odh-data-science-pipelines-argo-argoexec-rhel9, rhoai/odh-data-science-pipelines-argo-workflowcontroller-rhel9 Red Hat OpenShift Container Platform 4 cri-o, podman, openshift, podman-tests, podman-docker, podman-remote, +93 more Red Hat OpenShift Container Platform 5 cri-o, openshift, openshift5/ose-ptp-rhel9, openshift5/ose-tests-rhel9, openshift5/ose-dpu-cni-rhel9, openshift5/ose-hyperkube-rhel9, +39 more Red Hat Openshift Data Foundation 4 odf4/cephcsi-rhel9, odf4/odf-multicluster-rhel9-operator Red Hat OpenShift Dev Spaces devspaces/traefik-rhel9 Red Hat OpenShift Dev Workspaces Operator devworkspace/devworkspace-rhel9-operator, devworkspace/devworkspace-project-clone-rhel9 Red Hat OpenShift for Windows Containers openshift4-wincw/windows-machine-config-rhel9-operator, openshift4-wincw/windows-machine-config-operator-bundle Red Hat OpenShift GitOps microshift-gitops 1.19.2-36.el9, openshift-gitops-1/argocd-rhel8, openshift-gitops-1/argocd-rhel9, openshift-gitops-1/gitops-rhel8, openshift-gitops-1/gitops-rhel9, openshift-gitops-1/argocd-agent-rhel8, +6 more Red Hat OpenShift on AWS rosa 1.2.64-b2f7c89.el8 Red Hat OpenShift Virtualization 4 container-native-virtualization/cluster-network-addons-operator, container-native-virtualization/cluster-network-addons-operator-rhel9 Red Hat OpenStack Platform 16.2 rhosp-rhel8/osp-director-agent, rhosp-rhel8/osp-director-operator, rhosp-rhel8/osp-director-operator-bundle Red Hat OpenStack Platform 17.1 rhosp-rhel9/osp-director-agent, rhosp-rhel9/osp-director-operator, rhosp-rhel9/osp-director-operator-bundle Red Hat OpenStack Platform 18.0 rhoso-operators/octavia-rhel9-operator, rhoso-operators/prometheus-podman-exporter-rhel9 Red Hat Quay 3 quay/quay-builder-rhel8, quay/quay-builder-rhel9 Red Hat Trusted Artifact Signer rhtas/ec-rhel9, rhtas/cosign-rhel9, rhtas/fulcio-rhel9, rhtas/gitsign-rhel9, rhtas/rekor-cli-rhel9, rhtas/rekor-server-rhel9, +10 more Red Hat Security Profiles Operator compliance/openshift-security-profiles-rhel8-operator, compliance/openshift-security-profiles-operator-bundle Red Hat Zero Trust Workload Identity Manager zero-trust-workload-identity-manager/spiffe-spire-agent-rhel9, zero-trust-workload-identity-manager/spiffe-spire-server-rhel9, zero-trust-workload-identity-manager/spiffe-spire-oidc-discovery-provider-rhel9 Red Hat Zero Trust Workload Identity Manager - Tech Preview zero-trust-workload-identity-manager/spiffe-spire-agent-rhel9, zero-trust-workload-identity-manager/spiffe-spire-server-rhel9, zero-trust-workload-identity-manager/spiffe-spire-oidc-discovery-provider-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.17 cert-manager/cert-manager-operator-rhel9 1791788287, cert-manager/jetstack-cert-manager-rhel9 1791371069, cert-manager/jetstack-cert-manager-acmesolver-rhel9 1791371080
    fixed: vendor fix RHSA-2026:82322
  • Red Hat Enterprise Linux AppStream (v. 9) buildah 1.43.3-2.el9_8, buildah 1.43.4-2.el9_8, buildah-tests 1.43.3-2.el9_8, buildah-tests 1.43.4-2.el9_8
    fixed: vendor fix RHSA-2026:70640
  • Red Hat OpenShift AI 3.4 rhoai/odh-model-registry-rhel9 1791869365
    fixed: vendor fix RHSA-2026:84734
  • Red Hat OpenShift GitOps 1.22 openshift-gitops-1/gitops-promoter-rhel9 1793684735
    fixed: vendor fix RHSA-2026:94584
  • Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1791509689, rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-trainer-rhel9 1791869783, +99 more
    not affected: vulnerable code not present

2 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
2 mo ago

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 43% 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:N/I:N/A:H
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
go golang.org/x/crypto
<0.56.0
0.56.0

Affected products

  • golang.org/x/crypto golang.org/x/crypto/ssh

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

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.