---
title: "CVE-2026-56855\n    | Ubuntu"
description: Ubuntu is an open source software operating system that runs from the
  desktop, to the cloud, to all your internet connected things.
url: https://ubuntu.com/security/CVE-2026-56855?format=md
keywords: index, follow
---

# CVE-2026-56855

Publication date 3 September 2026

Last updated 4 September 2026

---

Ubuntu priority

**Medium**

[Why this priority?](https://ubuntu.com/security/cves/about#priority )

## Cvss 3 Severity Score

**7.5 · High**

[Score breakdown](https://ubuntu.com/security/CVE-2026-56855?format=md#impact-score)

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## Description

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.

## Status

Show unmaintained releases

| Package | Ubuntu Release | Status |
| --- | --- | --- |
| golang-1.17 | 26.04 LTS resolute | Not in release |
| 24.04 LTS noble | Not in release |
| 22.04 LTS jammy | Needs evaluation |
| golang-1.20 | 26.04 LTS resolute | Not in release |
| 24.04 LTS noble | Not in release |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| golang-1.21 | 26.04 LTS resolute | Not in release |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| golang-1.22 | 26.04 LTS resolute | Not in release |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| golang-1.23 | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| golang-1.24 | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| golang-1.25 | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Not in release |
| 22.04 LTS jammy | Not in release |
| golang-1.26 | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Not in release |
| 22.04 LTS jammy | Not in release |
| golang-1.27 | 26.04 LTS resolute | Not in release |
| 24.04 LTS noble | Not in release |
| 22.04 LTS jammy | Not in release |
| golang-defaults | 26.04 LTS resolute | Needs evaluation |
| 24.04 LTS noble | Needs evaluation |
| 22.04 LTS jammy | Needs evaluation |
| 20.04 LTS focal | Needs evaluation |
| 18.04 LTS bionic | Needs evaluation |
| 16.04 LTS xenial | Needs evaluation |

---

* [How can I get the fixes?](https://ubuntu.com/security/cves/about#security)
* [What do statuses mean?](https://ubuntu.com/security/cves/about#statuses)

## Severity score breakdown

CVSS version:
CVSS v3.0

**Base score**

7.5 · High

* Base metrics

  | Parameter | Value |
  | --- | --- |
  | Attack vector | Network |
  | Attack complexity | Low |
  | Privileges required | None |
  | User interaction | None |
  | Scope | Unchanged |
  | Confidentiality impact | None |
  | Integrity impact | None |
  | Availability impact | High |
* Scores

  | Parameter | Value |
  | --- | --- |
  | Base score | 7.5 · High |
  | Exploitability score | - |
  | Impact score | - |

**Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

## References

* [MITRE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-56855)
* [NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-56855)
* [Launchpad](https://launchpad.net/bugs/cve/CVE-2026-56855)
* [Debian](https://security-tracker.debian.org/tracker/CVE-2026-56855)

### Other references

* <https://www.cve.org/CVERecord?id=CVE-2026-56855>
* <https://go.dev/cl/826524>
* <https://go.dev/issue/81317>
* <https://groups.google.com/g/golang-announce/c/1y3fb2np35U>
* <https://pkg.go.dev/vuln/GO-2026-6355>