CVE-2026-59843

Publication date 21 July 2026

Last updated 25 August 2026

Ubuntu priority

Cvss 3 Severity Score

Description

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.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
libssh	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

Notes

mdeslaur

While this was mentioned in the 0.12.1 release notes, it was accidentally omitted and was included in 0.12.2 instead.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
libssh	Upstream: ?id=3f7 Upstream: ?id=006

Severity score breakdown

CVSS version: CVSS v3.0

Base score 6.5 · Medium

Base metrics

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

Scores

Parameter	Value
Base score	6.5 · Medium
Exploitability score	-
Impact score	-

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