CVE-2026-55655: Openssh: local mitm of x11 forwarding via abstract unix socket pre-binding in red hat enterprise linux openssh client versions

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.1%

Up from <0.1% on 22 Oct 2026.

EPSS score, percentile 2.1 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

5.0 Medium

CVSS v3.1 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (12)

Which versions are affected?

Unaffected 0:9.9p1-25.el10_2; 0:9.9p1-7.el10_0.5; 0:8.0p1-30.el8_10; 0:8.0p1-30.el8_10; 0:9.9p1-9.el9_8; 0:9.9p1-9.el9_8; and 14 more

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Workaround (from the CVE record)

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.

Advisories and patches

• RHSA-2026:36759 (Vendor advisory)
• RHSA-2026:47755 (Vendor advisory)
• RHSA-2026:47756 (Vendor advisory)
• RHSA-2026:47757 (Vendor advisory)
• RHSA-2026:54387 (Vendor advisory)
• RHSA-2026:58981 (Vendor advisory)
• RHSA-2026:76748 (Vendor advisory)
• RHSA-2026:76993 (Vendor advisory)
• RHSA-2026:80513 (Vendor advisory)
• RHSA-2026:82749 (Vendor advisory)
• RHSA-2026:82750 (Vendor advisory)
• RHSA-2026:82751 (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions not listed are: affected.

Versions the record lists as unaffected: 0:9.9p1-25.el10_2, 0:9.9p1-7.el10_0.5, 0:8.0p1-30.el8_10, 0:9.9p1-9.el9_8, 0:8.7p1-30.el9_2.13, 0:8.7p1-38.el9_4.10, 0:8.7p1-45.el9_6.5, 10.3p1-6.hum1.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

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 inp…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-55655 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 23 Jun 2026.
• The CVE record carries a CVSS v3.1 base score of 5.0 (Medium), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.1% (percentile 2.1), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact partial.
• The credits in the CVE record name AISLE as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

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

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.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline

Known exploited Red Hat vulnerabilities

• CVE-2015-3246: Red Hat Libuser Race Condition Vulnerability (added 26 Aug 2026)
• CVE-2015-5287: Red Hat Automatic Bug Reporting Tool Privilege Escalation Vulnerability (added 26 Aug 2026)
• CVE-2018-14667: Red Hat JBoss RichFaces Framework Expression Language Injection Vulnerability (added 28 Sep 2023)
• CVE-2021-3560: Red Hat Polkit Incorrect Authorization Vulnerability (added 12 May 2023)
• CVE-2021-4034: Red Hat Polkit Out-of-Bounds Read and Write Vulnerability (added 27 Jun 2022)