---
id: CVE-2026-59843
title: 'Libssh: libssh: denial of service via zero advertised channel packet size'
summary: >-
  A flaw was found in libssh. A remote authenticated peer can advertise a zero
  maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to
  loop indefinitely and consume CPU, leading to denial of service.
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-835
vendor: Red Hat
product: libssh
affected:
  - libssh (all versions)
  - libssh (all versions)
  - libssh (all versions)
  - libssh (all versions)
  - libssh (all versions)
  - libssh-main (all versions)
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-07-21T12:08:16.810909Z'
published: '2026-07-21'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T22:18:33.616Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-59843'
references:
  - url: 'https://access.redhat.com/errata/RHSA-2026:42922'
    label: 'RHSA-2026:42922'
  - url: 'https://access.redhat.com/errata/RHSA-2026:55855'
    label: 'RHSA-2026:55855'
  - url: 'https://access.redhat.com/errata/RHSA-2026:62217'
    label: 'RHSA-2026:62217'
  - url: 'https://access.redhat.com/errata/RHSA-2026:62218'
    label: 'RHSA-2026:62218'
  - url: 'https://access.redhat.com/security/cve/CVE-2026-59843'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2498176'
    label: RHBZ#2498176
tags:
  - cve.org
epss: 0.00567
epssPercentile: 0.47253
ingestedAt: '2026-11-05T23:41:31.948Z'
---

## Overview

A flaw was found in libssh. A remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.

## Affected

- `libssh (all versions)`
- `libssh (all versions)`
- `libssh (all versions)`
- `libssh (all versions)`
- `libssh (all versions)`
- `libssh-main (all versions)`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

### Workarounds

No workaround available.