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Advisory severityMedium5.0Red Hat Linux

Medium [CVE-2026-55655] Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Red Hat Enterprise Linux OpenSSH client versions

This medium-severity Red Hat Linux advisory covers CVE-2026-55655 affecting Red Hat Enterprise Linux 10.0 Extended Update Support, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

CVE-2026-55655 Source published Source updated

VulniPulse record published Record updated

CVE-2026-55655
Affected products & platforms
Red Hat LinuxRed Hat Enterprise Linux
Open source advisory

Summary

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.

This is a Moderate severity flaw. The OpenSSH client in Red Hat Enterprise Linux is vulnerable to a local man-in-the-middle attack on X11 forwarding connections.

Exploitation requires an attacker to have local unprivileged access on the client system and for X11 forwarding to be explicitly enabled and in use, which is not a default configuration. This vulnerability doesn't affect the upstream OpenSSH versions and is restricted to the versions as shipped with Red Hat Enterprise Linux.

Red Hat severity: Moderate — CVSS 5 (CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:L/A:N). Weakness: CWE-923.

Affected products named by the advisory: Red Hat Enterprise Linux 10.0 Extended Update Support; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions; Red Hat Enterprise Linux 9.6 Extended Update Support; and 10 more.

Is CVE-2026-55655 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-55655 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-55655?

Upgrade to a fixed release named by Red Hat:

  • openssh-0:9.9p1-25.el10_2
  • openssh-0:9.9p1-7.el10_0.5
  • openssh-0:8.0p1-30.el8_10
  • openssh-0:9.9p1-9.el9_8
  • openssh-0:8.7p1-38.el9_4.10
  • openssh-0:8.7p1-45.el9_6.5
  • openssh-main-10.3p1-6.hum1
  • rhai/base-image-cuda-rhel9:1791818590
  • rhai/base-image-cpu-rhel9:1791818589
  • rhai/base-image-spyre-rhel9:1791818505
  • rhai/base-image-tpu-rhel9:1791818496
  • rhai/base-image-rocm-rhel9:1791818502

38 more fixed releases are listed below.

Confirm against the vendor advisory before you patch.

Affected versions

No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Fixed versions
  • openssh-0:9.9p1-25.el10_2
  • openssh-0:9.9p1-7.el10_0.5
  • openssh-0:8.0p1-30.el8_10
  • openssh-0:9.9p1-9.el9_8
  • openssh-0:8.7p1-38.el9_4.10
  • openssh-0:8.7p1-45.el9_6.5
  • openssh-main-10.3p1-6.hum1
  • rhai/base-image-cuda-rhel9:1791818590
  • rhai/base-image-cpu-rhel9:1791818589
  • rhai/base-image-spyre-rhel9:1791818505
  • rhai/base-image-tpu-rhel9:1791818496
  • rhai/base-image-rocm-rhel9:1791818502
  • rhai/base-image-spyre-rhel9:1791818602
  • rhai/base-image-cpu-rhel9:1791818598
  • rhai/base-image-tpu-rhel9:1791818512
  • rhai/base-image-cuda-rhel9:1791818587
  • rhai/base-image-rocm-rhel9:1791818778
  • rhai/base-image-rocm-rhel9:1791818512
  • rhai/base-image-tpu-rhel9:1791818782
  • rhai/base-image-rocm-6.4-rhel9:1791818782
  • rhai/base-image-cuda-12.9-rhel9:1791818627
  • rhai/base-image-rocm-7.0-rhel9:1791818790
  • rhai/base-image-cpu-rhel9:1791818874
  • rhai/base-image-neuron-rhel9:1791818792
  • rhai/base-image-cuda-13.0-rhel9:1791818662
  • rhai/base-image-spyre-rhel9:1791818877
  • rhai/base-image-neuron-rhel9:1791883722
  • rhai/base-image-cuda-12.9-rhel9:1791881612
  • rhai/base-image-cpu-rhel9:1791885618
  • rhai/base-image-rocm-6.4-rhel9:1791881487
  • rhai/base-image-spyre-rhel9:1791881732
  • rhai/base-image-rocm-7.1-rhel9:1791883315
  • rhai/base-image-gaudi-rhel9:1791881486
  • rhai/base-image-tpu-rhel9:1791881769
  • rhai/base-image-cuda-13.0-rhel9:1791885505
  • rhai/base-image-spyre-rhel9:1791819252
  • rhai/base-image-gaudi-rhel9:1791818749
  • rhai/base-image-cpu-rhel9:1791819206
  • rhai/base-image-neuron-rhel9:1791818979
  • rhai/base-image-rocm-7.14-rhel9:1791819123
  • RHSA-2026:47757
  • RHSA-2026:76748
  • RHSA-2026:47755
  • RHSA-2026:47756
  • RHSA-2026:76993
  • RHSA-2026:80513
  • RHSA-2026:36759
  • RHSA-2026:82751
  • RHSA-2026:82761
  • RHSA-2026:82903

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • 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.

Official advisory · high-confidence parse· fetched 14 days ago·verify at source

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