{"id":"CVE-2026-56855","title":"golang.org/x/crypto/ssh: golang.org/x/crypto/ssh: Denial of Service via crafted messages (CVE-2026-56855)","summary":"A flaw was found in golang.org/x/crypto/ssh. After a channel has been established, a remote malicious peer could send specially crafted messages. This could lead to a deadlock of the entire connection, resulting in a Denial of Service (DoS…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","cvssSource":"vendor","cwe":"CWE-833","vendor":"Red Hat","product":"Red Hat OpenShift Container Platform 4","affected":["assisted_installer_for_red_hat_openshift_container_platform 2","builds_for_red_hat_openshift","confidential_compute_attestation","cryostat 4","external_secrets_operator_for_red_hat_openshift","multicluster_engine_for_kubernetes","openshift_api_for_data_protection","openshift_pipelines","openshift_serverless","advanced_cluster_management_for_kubernetes 2","advanced_cluster_security 4","ceph_storage 8","ceph_storage 9","edge_manager 1","enterprise_linux 10","enterprise_linux 8","enterprise_linux 9","openshift_ai_rhoai","openshift_container_platform 4","openshift_data_foundation 4","openshift_dev_spaces","openshift_dev_workspaces_operator","openshift_for_windows_containers","openshift_gitops","openshift_on_aws","openshift_virtualization 4","openstack_platform 16.2","openstack_platform 17.1","openstack_platform 18.0","quay 3","trusted_artifact_signer","security_profiles_operator","zero_trust_workload_identity_manager","zero_trust_workload_identity_manager_tech_preview","enterprise_linux_appstream_v_9","cert_manager_support_for_red_hat_openshift_release 1.17","openshift_ai 3.4"],"patched":["enterprise_linux_appstream_v_9","cert_manager_support_for_red_hat_openshift_release 1.17","openshift_ai 3.4"],"published":"2026-09-02","updated":"2026-10-19","sourceUpdated":"2026-10-19T11:46:47+00:00","source":"CSAF","sourceUrl":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56855.json","references":[{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56855.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-56855"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2528050"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-56855"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-56855"},{"url":"https://go.dev/cl/826524"},{"url":"https://go.dev/issue/81317"},{"url":"https://groups.google.com/g/golang-announce/c/1y3fb2np35U"},{"url":"https://pkg.go.dev/vuln/GO-2026-6355"},{"url":"https://access.redhat.com/errata/RHSA-2026:70640"},{"url":"https://access.redhat.com/errata/RHSA-2026:82322"},{"url":"https://access.redhat.com/errata/RHSA-2026:82304"},{"url":"https://access.redhat.com/errata/RHSA-2026:84734"}],"tags":["csaf","vex","red-hat","osv","go"],"epss":0.005,"epssPercentile":0.42643,"aliases":["GO-2026-6355"],"ecosystem":"go","ingestedAt":"2026-09-03T19:32:15.779Z","slug":"CVE-2026-56855","body":"## Overview\n\nA flaw was found in golang.org/x/crypto/ssh. After a channel has been established, a remote malicious peer could send specially crafted messages. This could lead to a deadlock of the entire connection, resulting in a Denial of Service (DoS) for the affected system.\n\n## Vendor advisories\n\n- **RHSA-2026:70640** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9) · released 2026-09-24 · [advisory](https://access.redhat.com/errata/RHSA-2026:70640)\n- **RHSA-2026:82322** · Red Hat · fixed in: Cert Manager support for Red Hat OpenShift release 1.17 · released 2026-10-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:82322)\n- **RHSA-2026:82304** · Red Hat · fixed in: Cert Manager support for Red Hat OpenShift release 1.17 · released 2026-10-13 · [advisory](https://access.redhat.com/errata/RHSA-2026:82304)\n- **RHSA-2026:84734** · Red Hat · fixed in: Red Hat OpenShift AI 3.4 · released 2026-10-19 · [advisory](https://access.redhat.com/errata/RHSA-2026:84734)\n- **Red Hat VEX** · Moderate · affected: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, Confidential Compute Attestation, Cryostat 4, External Secrets Operator for Red Hat OpenShift, Multicluster Engine for Kubernetes, … · no fix planned: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, Confidential Compute Attestation, Cryostat 4, … · updated 2026-10-19 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56855.json)\n\n**golang.org/x/crypto/ssh: golang.org/x/crypto/ssh: Denial of Service via crafted messages** — rated Moderate by Red Hat. Released 2026-09-02, updated 2026-10-19.\n\nAffected:\n\n- Assisted Installer for Red Hat OpenShift Container Platform 2\n- Builds for Red Hat OpenShift\n- Confidential Compute Attestation\n- Cryostat 4\n- External Secrets Operator for Red Hat OpenShift\n- Multicluster Engine for Kubernetes\n- OpenShift API for Data Protection\n- OpenShift Pipelines\n- OpenShift Serverless\n- Red Hat Advanced Cluster Management for Kubernetes 2\n- Red Hat Advanced Cluster Security 4\n- Red Hat Ceph Storage 8\n- Red Hat Ceph Storage 9\n- Red Hat Edge Manager 1\n- Red Hat Enterprise Linux 10\n- Red Hat Enterprise Linux 8\n- Red Hat Enterprise Linux 9\n- Red Hat OpenShift AI (RHOAI)\n- Red Hat OpenShift Container Platform 4\n- Red Hat Openshift Data Foundation 4\n- Red Hat OpenShift Dev Spaces\n- Red Hat OpenShift Dev Workspaces Operator\n- Red Hat OpenShift for Windows Containers\n- Red Hat OpenShift GitOps\n- Red Hat OpenShift on AWS\n- Red Hat OpenShift Virtualization 4\n- Red Hat OpenStack Platform 16.2\n- Red Hat OpenStack Platform 17.1\n- Red Hat OpenStack Platform 18.0\n- Red Hat Quay 3\n- Red Hat Trusted Artifact Signer\n- Security Profiles Operator\n- Zero Trust Workload Identity Manager\n- Zero Trust Workload Identity Manager - Tech Preview\n\nFixed:\n\n- Red Hat Enterprise Linux AppStream (v. 9)\n- Cert Manager support for Red Hat OpenShift release 1.17\n- Red Hat OpenShift AI 3.4\n\nNo fix planned:\n\n- Assisted Installer for Red Hat OpenShift Container Platform 2\n- Builds for Red Hat OpenShift\n- Confidential Compute Attestation\n- Cryostat 4\n- External Secrets Operator for Red Hat OpenShift\n- Multicluster Engine for Kubernetes\n- OpenShift API for Data Protection\n- OpenShift Pipelines\n- OpenShift Serverless\n- Red Hat Advanced Cluster Management for Kubernetes 2\n- Red Hat Advanced Cluster Security 4\n- Red Hat Ceph Storage 8\n- Red Hat Ceph Storage 9\n- Red Hat Edge Manager 1\n- Red Hat Enterprise Linux 10\n- Red Hat Enterprise Linux 8\n- Red Hat Enterprise Linux 9\n- Red Hat OpenShift AI (RHOAI)\n- Red Hat OpenShift Container Platform 4\n- Red Hat Openshift Data Foundation 4\n- Red Hat OpenShift Dev Spaces\n- Red Hat OpenShift Dev Workspaces Operator\n- Red Hat OpenShift for Windows Containers\n- Red Hat OpenShift GitOps\n- Red Hat OpenShift on AWS\n- Red Hat OpenShift Virtualization 4\n- Red Hat OpenStack Platform 16.2\n- Red Hat OpenStack Platform 17.1\n- Red Hat OpenStack Platform 18.0\n- Red Hat Quay 3\n- Red Hat Trusted Artifact Signer\n- Security Profiles Operator\n- Zero Trust Workload Identity Manager\n- Zero Trust Workload Identity Manager - Tech Preview\n\nNot affected:\n\n- Red Hat OpenShift AI 3.4\n\n## Remediation\n\nBefore applying this update, make sure all previously released errata\nrelevant to your system have been applied.\n\nFor details on how to apply this update, refer to:\n\nhttps://access.redhat.com/articles/11258 https://access.redhat.com/errata/RHSA-2026:70640\nBefore applying this update, make sure all previously released errata relevant to your system have been applied.\n\nThe steps to apply the upgraded images are different depending on the installation plan approval policy you used\nwhen installing the cert-manager Operator for Red Hat OpenShift.\n\n- If the approval policy is set to `Automatic`, then the Operator will be upgraded automatically when there is a\nnew version of the Operator. No further action is required to upgrade. This is the default setting.\n\n- If you changed the approval policy to `Manual`, then you must manually approve the upgrade… https://access.redhat.com/errata/RHSA-2026:82322\nBefore applying this update, make sure all previously released errata relevant to your system have been applied.\n\nThe steps to apply the upgraded images are different depending on the installation plan approval policy you used\nwhen installing the cert-manager Operator for Red Hat OpenShift.\n\n- If the approval policy is set to `Automatic`, then the Operator will be upgraded automatically when there is a\nnew version of the Operator. No further action is required to upgrade. This is the default setting.\n\n- If you changed the approval policy to `Manual`, then you must manually approve the upgrade… https://access.redhat.com/errata/RHSA-2026:82304\n\nWorkarounds / mitigations:\n\n- Red Hat is not aware of a practical mitigation that fully prevents this issue while maintaining affected SSH functionality. Where operationally possible, restrict SSH connectivity to trusted systems. Apply relevant Red Hat updates when they become available.\n\n## Package advisory (CVE-2026-56855)\n\nAffected packages:\n\n- `golang.org/x/crypto < 0.56.0`\n\nPatched in:\n\n- `golang.org/x/crypto 0.56.0`\n\nSource: https://osv.dev/vulnerability/GO-2026-6355","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":201797,"id":"CVE-2026-56855","ts":1789399725858,"field":"cvss","old":null,"new":"5.3"},{"seq":201796,"id":"CVE-2026-56855","ts":1789399725858,"field":"severity","old":"none","new":"medium"},{"seq":200527,"id":"CVE-2026-56855","ts":1789397373785,"field":"cvss","old":"5.3","new":null},{"seq":200526,"id":"CVE-2026-56855","ts":1789397373785,"field":"severity","old":"medium","new":"none"},{"seq":198444,"id":"CVE-2026-56855","ts":1789391968805,"field":"cvss","old":null,"new":"5.3"},{"seq":198443,"id":"CVE-2026-56855","ts":1789391968805,"field":"severity","old":"none","new":"medium"},{"seq":196237,"id":"CVE-2026-56855","ts":1789383585211,"field":"cvss","old":"5.3","new":null},{"seq":196236,"id":"CVE-2026-56855","ts":1789383585211,"field":"severity","old":"medium","new":"none"},{"seq":195166,"id":"CVE-2026-56855","ts":1789380475055,"field":"cvss","old":null,"new":"5.3"},{"seq":195165,"id":"CVE-2026-56855","ts":1789380475055,"field":"severity","old":"none","new":"medium"},{"seq":193953,"id":"CVE-2026-56855","ts":1789378515615,"field":"cvss","old":"5.3","new":null},{"seq":193952,"id":"CVE-2026-56855","ts":1789378515615,"field":"severity","old":"medium","new":"none"},{"seq":192740,"id":"CVE-2026-56855","ts":1789376407141,"field":"cvss","old":null,"new":"5.3"},{"seq":192739,"id":"CVE-2026-56855","ts":1789376407141,"field":"severity","old":"none","new":"medium"},{"seq":191527,"id":"CVE-2026-56855","ts":1789373419697,"field":"cvss","old":"5.3","new":null},{"seq":191526,"id":"CVE-2026-56855","ts":1789373419697,"field":"severity","old":"medium","new":"none"},{"seq":190312,"id":"CVE-2026-56855","ts":1789369300007,"field":"cvss","old":null,"new":"5.3"},{"seq":190311,"id":"CVE-2026-56855","ts":1789369300007,"field":"severity","old":"none","new":"medium"},{"seq":189099,"id":"CVE-2026-56855","ts":1789368266967,"field":"cvss","old":"5.3","new":null},{"seq":189098,"id":"CVE-2026-56855","ts":1789368266967,"field":"severity","old":"medium","new":"none"},{"seq":187882,"id":"CVE-2026-56855","ts":1789365143354,"field":"cvss","old":null,"new":"5.3"},{"seq":187881,"id":"CVE-2026-56855","ts":1789365143354,"field":"severity","old":"none","new":"medium"},{"seq":186669,"id":"CVE-2026-56855","ts":1789363271406,"field":"cvss","old":"5.3","new":null},{"seq":186668,"id":"CVE-2026-56855","ts":1789363271406,"field":"severity","old":"medium","new":"none"},{"seq":185455,"id":"CVE-2026-56855","ts":1789361101334,"field":"cvss","old":null,"new":"5.3"},{"seq":185454,"id":"CVE-2026-56855","ts":1789361101334,"field":"severity","old":"none","new":"medium"},{"seq":184242,"id":"CVE-2026-56855","ts":1789358155668,"field":"cvss","old":"5.3","new":null},{"seq":184241,"id":"CVE-2026-56855","ts":1789358155668,"field":"severity","old":"medium","new":"none"},{"seq":182493,"id":"CVE-2026-56855","ts":1789354222473,"field":"cvss","old":null,"new":"5.3"},{"seq":182492,"id":"CVE-2026-56855","ts":1789354222473,"field":"severity","old":"none","new":"medium"},{"seq":181286,"id":"CVE-2026-56855","ts":1789353120610,"field":"cvss","old":"5.3","new":null},{"seq":181285,"id":"CVE-2026-56855","ts":1789353120610,"field":"severity","old":"medium","new":"none"},{"seq":180079,"id":"CVE-2026-56855","ts":1789350169126,"field":"cvss","old":null,"new":"5.3"},{"seq":180078,"id":"CVE-2026-56855","ts":1789350169126,"field":"severity","old":"none","new":"medium"},{"seq":178872,"id":"CVE-2026-56855","ts":1789348101411,"field":"cvss","old":"5.3","new":null},{"seq":178871,"id":"CVE-2026-56855","ts":1789348101411,"field":"severity","old":"medium","new":"none"},{"seq":177665,"id":"CVE-2026-56855","ts":1789346277623,"field":"cvss","old":null,"new":"5.3"},{"seq":177664,"id":"CVE-2026-56855","ts":1789346277623,"field":"severity","old":"none","new":"medium"},{"seq":176458,"id":"CVE-2026-56855","ts":1789343018781,"field":"cvss","old":"5.3","new":null},{"seq":176457,"id":"CVE-2026-56855","ts":1789343018781,"field":"severity","old":"medium","new":"none"},{"seq":174575,"id":"CVE-2026-56855","ts":1789334771619,"field":"cvss","old":null,"new":"5.3"},{"seq":174574,"id":"CVE-2026-56855","ts":1789334771619,"field":"severity","old":"none","new":"medium"},{"seq":173370,"id":"CVE-2026-56855","ts":1789333512388,"field":"cvss","old":"5.3","new":null},{"seq":173369,"id":"CVE-2026-56855","ts":1789333512388,"field":"severity","old":"medium","new":"none"},{"seq":172184,"id":"CVE-2026-56855","ts":1789331018051,"field":"cvss","old":null,"new":"5.3"},{"seq":172183,"id":"CVE-2026-56855","ts":1789331018051,"field":"severity","old":"none","new":"medium"},{"seq":170998,"id":"CVE-2026-56855","ts":1789328614594,"field":"cvss","old":"5.3","new":null},{"seq":170997,"id":"CVE-2026-56855","ts":1789328614594,"field":"severity","old":"medium","new":"none"},{"seq":169793,"id":"CVE-2026-56855","ts":1789327051000,"field":"cvss","old":null,"new":"5.3"},{"seq":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