Openssh: local mitm of x11 forwarding via abstract unix socket pre-binding in red hat enterprise linux openssh client versions

Summary

CVE	CVE-2026-55655
State	PUBLISHED
Assigner	redhat
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-06-23 04:17:40 UTC
Updated	2026-07-08 14:17:14 UTC
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.

Risk And Classification

Primary CVSS: v3.1 6.1 MEDIUM from [email protected]

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

EPSS: 0.000900000 probability, percentile 0.005730000 (date 2026-07-09)

Problem Types: CWE-923 | CWE-923 Improper Restriction of Communication Channel to Intended Endpoints

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Primary	6.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N`
3.1	[email protected]	Secondary	5	MEDIUM	`CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N`
3.1	CNA	CVSS	5	MEDIUM	`CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N`

CVSS v3.1 Breakdown

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

Low

Availability

None

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

NVD Known Affected Configurations (CPE 2.3)

Type	Vendor	Product	Version	Update	Edition	Language
Application	Openbsd	Openssh	-	All	All	All
Operating System	Redhat	Enterprise Linux	10.0	All	All	All
Operating System	Redhat	Enterprise Linux	6.0	All	All	All
Operating System	Redhat	Enterprise Linux	7.0	All	All	All
Operating System	Redhat	Enterprise Linux	8.0	All	All	All
Operating System	Redhat	Enterprise Linux	9.0	All	All	All

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Red Hat	Red Hat Hardened Images	unaffected 10.3p1-6.hum1 * rpm	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 10	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 6	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 7	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 8	Not specified	Not specified
CNA	Red Hat	Red Hat Enterprise Linux 9	Not specified	Not specified
CNA	Red Hat	Red Hat OpenShift Container Platform 4	Not specified	Not specified

References

Reference	Source	Link	Tags
access.redhat.com/security/cve/CVE-2026-55655	[email protected]	access.redhat.com	Vendor Advisory
bugzilla.redhat.com/show_bug.cgi	[email protected]	bugzilla.redhat.com	Issue Tracking, Vendor Advisory
access.redhat.com/errata/RHSA-2026:36759	[email protected]	access.redhat.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

Additional Advisory Data

Source	Time	Event
CNA	2026-04-26T18:39:13.000Z	Reported to Red Hat.
CNA	2026-06-22T23:22:11.127Z	Made public.

Workarounds

CNA: To mitigate this issue, disable X11 forwarding on OpenSSH clients when it is not required. This can be achieved by avoiding the use of `-X` or `-Y` options when invoking `ssh`, or by setting `ForwardX11 no` in the SSH client configuration file (`~/.ssh/config` or `/etc/ssh/ssh_config`). Disabling X11 forwarding will prevent the client from attempting to establish X11 connections, thereby removing the attack vector.

There are currently no legacy QID mappings associated with this CVE.