---
id: CVE-2026-56855
aliases:
  - GO-2026-6355
title: Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh
summary: Prevent DoS on deadlocked established channel in golang.org/x/crypto/ssh
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'
vendor: x
product: golang.org/x/crypto
ecosystem: go
affected:
  - golang.org/x/crypto < 0.56.0
patched:
  - golang.org/x/crypto 0.56.0
published: '2026-09-02'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T10:41:42.556134596Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GO-2026-6355'
references:
  - url: 'https://go.dev/issue/81317'
  - url: 'https://go.dev/cl/826524'
  - url: 'https://groups.google.com/g/golang-announce/c/1y3fb2np35U'
  - 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://pkg.go.dev/vuln/GO-2026-6355'
  - url: 'https://access.redhat.com/errata/RHSA-2026:70640'
tags:
  - osv
  - go
  - csaf
  - vex
  - red-hat
epss: 0.0062
epssPercentile: 0.47398
cvssSource: vendor
cwe:
  - CWE-833
ingestedAt: '2026-09-03T19:32:15.779Z'
---

## Overview

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.

## Affected packages

- `golang.org/x/crypto < 0.56.0`

## Remediation

Upgrade to a patched release:

- `golang.org/x/crypto 0.56.0`

## Vendor advisories

- **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)
- **Red Hat VEX** · Moderate · affected: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, Confidential Compute Attestation, Cryostat 4, External Secrets Operator for Red Hat OpenShift, … · no fix planned: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, Confidential Compute Attestation, … · updated 2026-09-24 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56855.json)