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.

An update of the openssh package has been released.

The remote Oracle Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-47755 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       Resolves: RHEL-185775

Tenable has extracted the preceding description block directly from the Oracle Linux 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 AlmaLinux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the ALSA-2026:47756 advisory.

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in AlmaLinux OpenSSH client     versions (CVE-2026-55655)
      * openssh: Double free in AlmaLinux versions of OpenSSH DH-GEX client path during FIPS known-group     validation leads to client-side denial of service (CVE-2026-55653)
      * openssh: Heap out-of-bounds read in AlmaLinux versions of OpenSSH GSSAPI indicator cleanup due to     missing NULL sentinel termination (CVE-2026-55654)
      * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)
      * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

Tenable has extracted the preceding description block directly from the AlmaLinux 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 RockyLinux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:47756 advisory.

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client     versions (CVE-2026-55655)

    * openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group     validation leads to client-side denial of service (CVE-2026-55653)

    * openssh: Heap out-of-bounds read in Rocky Linux versions of OpenSSH GSSAPI indicator cleanup due to     missing NULL sentinel termination (CVE-2026-55654)

    * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)

    * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

Tenable has extracted the preceding description block directly from the RockyLinux 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 AlmaLinux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the ALSA-2026:47757 advisory.

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in AlmaLinux OpenSSH client     versions (CVE-2026-55655)
      * openssh: Double free in AlmaLinux versions of OpenSSH DH-GEX client path during FIPS known-group     validation leads to client-side denial of service (CVE-2026-55653)
      * openssh: Heap out-of-bounds read in AlmaLinux versions of OpenSSH GSSAPI indicator cleanup due to     missing NULL sentinel termination (CVE-2026-55654)
      * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)
      * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

Tenable has extracted the preceding description block directly from the AlmaLinux 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 Oracle Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-47757 advisory.

    - CVE-2026-59996: Fix remote glob result of '..' causing files to be placed       in unintended parent directories when scp performs remote-to-remote copy       via the local host       Resolves: RHEL-193170
    - CVE-2026-60002: Fix use-after-free in cached hostkey during key re-exchange       Resolves: RHEL-193016
    - 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       Resolves: RHEL-186435
    - CVE-2026-55654: Fix heap out-of-bounds read during GSSAPI indicator       cleanup due to missing NULL terminator       Resolves: RHEL-185826

Tenable has extracted the preceding description block directly from the Oracle Linux 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 Redhat Enterprise Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:47755 advisory.

    OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating     systems. It includes the core files necessary for both the OpenSSH client and server.

    Security Fix(es):

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Red Hat Enterprise Linux     OpenSSH client versions (CVE-2026-55655)

    * openssh: Double free in Red Hat Enterprise Linux versions of OpenSSH DH-GEX client path during FIPS     known-group validation leads to client-side denial of service (CVE-2026-55653)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 Redhat Enterprise Linux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:47756 advisory.

    OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating     systems. It includes the core files necessary for both the OpenSSH client and server.

    Security Fix(es):

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Red Hat Enterprise Linux     OpenSSH client versions (CVE-2026-55655)

    * openssh: Double free in Red Hat Enterprise Linux versions of OpenSSH DH-GEX client path during FIPS     known-group validation leads to client-side denial of service (CVE-2026-55653)

    * openssh: Heap out-of-bounds read in Red Hat Enterprise Linux versions of OpenSSH GSSAPI indicator     cleanup due to missing NULL sentinel termination (CVE-2026-55654)

    * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)

    * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 Redhat Enterprise Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:47757 advisory.

    OpenSSH is an SSH protocol implementation supported by a number of Linux, UNIX, and similar operating     systems. It includes the core files necessary for both the OpenSSH client and server.

    Security Fix(es):

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Red Hat Enterprise Linux     OpenSSH client versions (CVE-2026-55655)

    * openssh: Double free in Red Hat Enterprise Linux versions of OpenSSH DH-GEX client path during FIPS     known-group validation leads to client-side denial of service (CVE-2026-55653)

    * openssh: Heap out-of-bounds read in Red Hat Enterprise Linux versions of OpenSSH GSSAPI indicator     cleanup due to missing NULL sentinel termination (CVE-2026-55654)

    * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)

    * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

    For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and     other related information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux 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 RockyLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:47755 advisory.

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client     versions (CVE-2026-55655)

    * openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group     validation leads to client-side denial of service (CVE-2026-55653)

Tenable has extracted the preceding description block directly from the RockyLinux 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 RockyLinux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:47757 advisory.

    * openssh: Local MITM of X11 forwarding via abstract UNIX socket pre-binding in Rocky Linux OpenSSH client     versions (CVE-2026-55655)

    * openssh: Double free in Rocky Linux versions of OpenSSH DH-GEX client path during FIPS known-group     validation leads to client-side denial of service (CVE-2026-55653)

    * openssh: Heap out-of-bounds read in Rocky Linux versions of OpenSSH GSSAPI indicator cleanup due to     missing NULL sentinel termination (CVE-2026-55654)

    * openssh: OpenSSH: Use-after-free vulnerability during host key re-exchange on the client side     (CVE-2026-60002)

    * openssh: OpenSSH: `scp` file misplacement vulnerability during remote copy (CVE-2026-59996)

Tenable has extracted the preceding description block directly from the RockyLinux 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 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
331582	Photon OS 5.0: Openssh PHSA-2026-5.0-0936	Nessus	PhotonOS Local Security Checks	high
331539	Oracle Linux 8 : openssh (ELSA-2026-47755)	Nessus	Oracle Linux Local Security Checks	medium
331475	AlmaLinux 9 : openssh (ALSA-2026:47756)	Nessus	Alma Linux Local Security Checks	critical
331313	RockyLinux 9 : openssh (RLSA-2026:47756)	Nessus	Rocky Linux Local Security Checks	critical
331288	AlmaLinux 10 : openssh (ALSA-2026:47757)	Nessus	Alma Linux Local Security Checks	critical
331287	Oracle Linux 10 : openssh (ELSA-2026-47757)	Nessus	Oracle Linux Local Security Checks	critical
330865	RHEL 8 : openssh (RHSA-2026:47755)	Nessus	Red Hat Local Security Checks	medium
330864	RHEL 9 : openssh (RHSA-2026:47756)	Nessus	Red Hat Local Security Checks	critical
330850	RHEL 10 : openssh (RHSA-2026:47757)	Nessus	Red Hat Local Security Checks	critical
330845	RockyLinux 8 : openssh (RLSA-2026:47755)	Nessus	Rocky Linux Local Security Checks	medium
330844	RockyLinux 10 : openssh (RLSA-2026:47757)	Nessus	Rocky Linux Local Security Checks	critical
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

Analytics

CVE-2026-55655

medium

Tenable Plugins

high

medium

critical

critical

critical

critical

medium

critical

critical

medium

critical

medium

medium

medium