CVE-2026-55655
Publication date 23 June 2026
Last updated 29 June 2026
Ubuntu priority
Description
A flaw was found in OpenSSH. A local unprivileged attacker on a Linux client host can hijack client-side X11 forwarding connections. This is possible by pre-binding the preferred abstract X socket name when X11 forwarding is enabled and a local UNIX-domain X socket is used. A successful attack can compromise the confidentiality of forwarded X11 traffic, including sensitive window contents and input, and may allow some manipulation of the forwarded session.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| openssh | 26.04 LTS resolute |
Vulnerable, fix deferred
|
| 25.10 questing |
Vulnerable, fix deferred
|
|
| 24.04 LTS noble |
Vulnerable, fix deferred
|
|
| 22.04 LTS jammy |
Vulnerable, fix deferred
|
|
| 20.04 LTS focal |
Vulnerable, fix deferred
|
|
| 18.04 LTS bionic |
Vulnerable, fix deferred
|
|
| 16.04 LTS xenial |
Vulnerable, fix deferred
|
|
| 14.04 LTS trusty |
Vulnerable, fix deferred
|
|
| openssh-ssh1 | 26.04 LTS resolute | Ignored |
| 25.10 questing | Ignored | |
| 24.04 LTS noble | Ignored | |
| 22.04 LTS jammy | Ignored | |
| 20.04 LTS focal | Ignored | |
| 18.04 LTS bionic | Ignored |
Notes
mdeslaur
openssh-ssh1 is only provided for compatibility with old devices that cannot be upgraded to modern protocols. We will not be providing any security support for the openssh-ssh1 package as it is insecure and should be used in trusted environments only. not details on a possible fix as of 2026-06-29, marking as deferred
Severity score breakdown
CVSS version: CVSS v3.0
Base score
5.0 · Medium
Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N