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.

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-95b955a09b advisory.

    - CVE-2026-55653: Fix double free in openssh DH-GEX client path during FIPS known-group validation that     leads to client-side denial of service
    - CVE-2026-55654: Fix heap out-of-bounds read during GSSAPI indicator cleanup due to missing NULL     terminator
    - CVE-2026-55655: Fix MITM of X11 forwarding via abstract UNIX socket pre-binding

Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-a80275b42d advisory.

    Improve GSS KEX algorithms documentation

    ----

    - CVE-2026-55653: Fix double free in openssh DH-GEX client path during FIPS known-group validation that     leads to client-side denial of service
    - CVE-2026-55654: Fix heap out-of-bounds read during GSSAPI indicator cleanup due to missing NULL     terminator
    - CVE-2026-55655: Fix MITM of X11 forwarding via abstract UNIX socket pre-binding

Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-55655)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
326360	Fedora 43 : openssh (2026-95b955a09b)	Nessus	Fedora Local Security Checks	medium
325835	Fedora 44 : openssh (2026-a80275b42d)	Nessus	Fedora Local Security Checks	medium
322158	Linux Distros Unpatched Vulnerability : CVE-2026-55655	Nessus	Misc.	medium

Detections

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CVE-2026-55655

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Tenable Plugins

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