Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh
Priority LOW 39CWE-770Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Partial Red Hat: 4 fixed, 35 without a fix
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat. Impact type from CWE-770.
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.005 43rd percentileScored 2026-11-07
Fix Partial golang.org/x/crypto/ssh (golang.org/x/crypto): 0.56.0Red Hat: 6 advisoriesRed Hat: 4 fixed, 35 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Go standard library | golang.org/x/crypto/ssh | before 0.56.0 | 0.56.0 | Patch available | CNA |
- golang.org/x/crypto/ssh VendorGo standard library Affected before 0.56.0 Fixed in 0.56.0 Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:golang:crypto:*:*:*:*:*:go:*:* | before 0.56.0 | Vulnerable | Go standard library |
- cpe:2.3:a:golang:crypto:*:*:*:*:*:go:*:* Versions before 0.56.0 Vulnerable ·Go standard library
Remediation
- Fix · CNA golang.org/x/crypto/ssh (golang.org/x/crypto) Fixed in 0.56.0
Red Hat 6 advisories
- RHSA-2026:94584 Released 2026-11-03 · Red Hat rating CriticalImportant: Red Hat OpenShift GitOps v1.22.3 security update
- Red Hat OpenShift GitOps 1.22 registry.redhat.io/openshift-gitops-1/argo-rollouts-rhel9, registry.redhat.io/openshift-gitops-1/argocd-agent-rhel9, registry.redhat.io/openshift-gitops-1/argocd-extensions-rhel9 +10
- RHSA-2026:90424 Released 2026-10-26 · Red Hat rating Importantbuildah security update
- Red Hat Enterprise Linux AppStream (v. 9) buildah-2:1.43.4-2.el9_8, buildah-tests-2:1.43.4-2.el9_8
- RHSA-2026:84734 Released 2026-10-19 · Red Hat rating CriticalRHOAI 3.4.5 - Red Hat OpenShift AI
- Red Hat OpenShift AI 3.4 registry.redhat.io/rhoai/odh-ai-gateway-payload-processing-rhel9, registry.redhat.io/rhoai/odh-automl-rhel9, registry.redhat.io/rhoai/odh-autorag-rhel9 +47
Show 3 more Red Hat advisories
- RHSA-2026:82322 Released 2026-10-13 · Red Hat rating Importantcert-manager Operator for Red Hat OpenShift 1.17.2
- Cert Manager support for Red Hat OpenShift release 1.17 registry.redhat.io/cert-manager/cert-manager-operator-rhel9
- RHSA-2026:82304 Released 2026-10-13 · Red Hat rating Importantcert-manager Operator for Red Hat OpenShift 1.17.2
- Cert Manager support for Red Hat OpenShift release 1.17 registry.redhat.io/cert-manager/jetstack-cert-manager-acmesolver-rhel9, registry.redhat.io/cert-manager/jetstack-cert-manager-rhel9
- RHSA-2026:70640 Released 2026-09-24 · Red Hat rating Importantbuildah security update
- Red Hat Enterprise Linux AppStream (v. 9) buildah-2:1.43.3-2.el9_8, buildah-tests-2:1.43.3-2.el9_8
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
golang.org/x/crypto/ssh 0.56.0
2 records Highest priority Priority LOW 2 LOW
Other records, highest priority first
- TI-2026-54686 Prevent DoS on deadlocked undecided channel in golang.org/x/crypto/sshPriority LOW 39
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Assisted Installer for Red Hat OpenShift Container Platform 2 | Affected | No fix yet: Fix deferred |
| Builds for Red Hat OpenShift | Affected | No fix yet: Fix deferred |
| Confidential Compute Attestation | Affected | No fix yet: Fix deferred |
| Cryostat 4 | Affected | No fix yet: Fix deferred |
| External Secrets Operator for Red Hat OpenShift | Affected | No fix yet: Fix deferred |
| Multicluster Engine for Kubernetes | Affected | No fix yet: Fix deferred |
| OpenShift API for Data Protection | Affected | No fix yet: Fix deferred |
| OpenShift Pipelines | Affected | No fix yet: Fix deferred |
| OpenShift Serverless | Affected | No fix yet: Fix deferred |
| Red Hat Advanced Cluster Management for Kubernetes 2 | Affected | No fix yet: Fix deferred |
| Red Hat Advanced Cluster Security 4 | Affected | No fix yet: Fix deferred |
| Red Hat Ceph Storage 8 | Affected | No fix yet: Fix deferred |
| Red Hat Ceph Storage 9 | Affected | No fix yet: Fix deferred |
| Red Hat Edge Manager 1 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 10 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 8 | Affected | No fix yet: Fix deferred |
| Red Hat Enterprise Linux 9 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet |
| Red Hat OpenShift Container Platform 5 | Affected | No fix yet |
| Red Hat OpenShift Dev Spaces | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Dev Workspaces Operator | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift GitOps | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Virtualization 4 | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift for Windows Containers | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift on AWS | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 16.2 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 17.1 | Affected | No fix yet: Fix deferred |
| Red Hat OpenStack Platform 18.0 | Affected | No fix yet: Fix deferred |
| Red Hat Openshift Data Foundation 4 | Affected | No fix yet: Fix deferred |
| Red Hat Quay 3 | Affected | No fix yet: Fix deferred |
| Red Hat Trusted Artifact Signer | Affected | No fix yet: Fix deferred |
| Security Profiles Operator | Affected | No fix yet: Fix deferred |
| Zero Trust Workload Identity Manager | Affected | No fix yet: Fix deferred |
| Zero Trust Workload Identity Manager - Tech Preview | Affected | No fix yet: Fix deferred |
| Cert Manager support for Red Hat OpenShift release 1.17 | Fixed | RHSA-2026:82304, RHSA-2026:82322 |
| Red Hat Enterprise Linux AppStream (v. 9) | Fixed | RHSA-2026:70640, RHSA-2026:90424 |
| Red Hat OpenShift AI 3.4 | Fixed | RHSA-2026:84734 |
| Red Hat OpenShift GitOps 1.22 | Fixed | RHSA-2026:94584 |
Not affected: 3 products
- Red Hat OpenShift AI 3.4
- Red Hat OpenShift Container Platform 5
- Red Hat OpenShift GitOps 1.22
Timeline
- 2026-10-02 Threatist record created from CVE-2026-56855
- 2026-10-11 Affected versions changed · Red Hat
- 2026-10-13 Affected versions changed · Red Hat
- 2026-10-14 Fix available: RHSA-2026:82304 · Red Hat
- 2026-10-14 Fix available: RHSA-2026:82322 · Red Hat
- 2026-10-15 Fix available: Cert Manager support for Red Hat OpenShift release 1.17 · Red Hat
- 2026-10-20 Fix available: RHSA-2026:84734 · Red Hat
- 2026-10-20 Fix available: Red Hat OpenShift AI 3.4 · Red Hat
- 2026-10-27 Affected versions changed · Red Hat
- 2026-10-29 Fix available: RHSA-2026:90424 · Red Hat
- 2026-10-30 Affected versions changed · Red Hat
- 2026-11-04 Fix available: RHSA-2026:94584 · Red Hat
- 2026-11-04 Fix available: Red Hat OpenShift GitOps 1.22 · Red Hat
References
More Go standard library Crypto vulnerabilities
- TI-2023-26623 The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6… CVSS 3.1MEDIUM 5.9
- TI-2026-30791 Invoking auth bypass via unenforced @revoked status in golang.org/x/crypto/ssh/knownhosts CVSS 3.1CRITICAL 9.1
- TI-2026-34255 Invoking VerifiedPublicKeyCallback permissions skip enforcement in golang.org/x/crypto/ssh CVSS 3.1CRITICAL 10.0
- TI-2026-28715 Invoking key constraints not enforced in golang.org/x/crypto/ssh/agent CVSS 3.1CRITICAL 9.1
- TI-2026-28714 Invoking agent constraints dropped when forwarding keys in golang.org/x/crypto/ssh/agent CVSS 3.1CRITICAL 9.1
- TI-2026-28713 Invoking bypass of FIDO/U2F security keys physical interaction in golang.org/x/crypto/ssh CVSS 3.1CRITICAL 9.1
Sources
- CVE-2026-56855 · CVE Program
- CVE-2026-56855 · NVD
- FIRST EPSS
- CVE-2026-56855 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences