A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

An update of the openssh package has been released.

The version of OpenSSH installed on the remote host is prior to 9.9p2. It is, therefore, affected by a man in the middle (MITM) vulnerability. ssh(1) in OpenSSH versions 6.8p1 to 9.9p1 (inclusive) contained a logic error that allowed an on-path attacker (a.k.a MITM) to impersonate any server when the VerifyHostKeyDNS option is enabled. This option is off by default.

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

The remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 / openSUSE 15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2025:0585-1 advisory.

    - CVE-2025-26465: Fixed MitM attack against OpenSSH's VerifyHostKeyDNS-enabled client (bsc#1237040).
    - CVE-2025-26466: Fixed DoS attack against OpenSSH's client and server (bsc#1237041).

Tenable has extracted the preceding description block directly from the SUSE 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 Ubuntu 16.04 LTS / 18.04 LTS host has packages installed that are affected by a vulnerability as referenced in the USN-7270-2 advisory.

    USN-7270-1 fixed a vulnerability in OpenSSH. This update provides the corresponding update for Ubuntu     16.04 LTS and Ubuntu 18.04 LTS.



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

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

The remote host is affected by the vulnerability described in GLSA-202502-01 (OpenSSH: Multiple Vulnerabilities)

    Multiple vulnerabilities have been discovered in OpenSSH. Please review the CVE identifiers referenced     below for details.

Tenable has extracted the preceding description block directly from the Gentoo 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 version of openssh installed on the remote host is prior to 9.9p2. It is, therefore, affected by multiple vulnerabilities as referenced in the SSA:2025-049-01 advisory.

    New openssh packages are available for Slackware 15.0 and -current to fix security issues.

Tenable has extracted the preceding description block directly from the openssh 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 Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS / 24.10 host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-7270-1 advisory.

    It was discovered that the OpenSSH client incorrectly handled the non-default VerifyHostKeyDNS option. If     that option were enabled, an attacker could possibly impersonate a server by completely bypassing the     server identity check. (CVE-2025-26465)

    It was discovered that OpenSSH incorrectly handled the transport-level ping facility. A remote attacker     could possibly use this issue to cause OpenSSH clients and servers to consume resources, leading to a     denial of service. This issue only affected Ubuntu 24.04 LTS and Ubuntu 24.10. (CVE-2025-26466)

Tenable has extracted the preceding description block directly from the Ubuntu 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 Debian 12 host has packages installed that are affected by a vulnerability as referenced in the dsa-5868 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-5868-1                   security@debian.org     https://www.debian.org/security/                     Salvatore Bonaccorso     February 18, 2025                     https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : openssh     CVE ID         : CVE-2025-26465

    The Qualys Threat Research Unit (TRU) discovered that the OpenSSH client     is vulnerable to a machine-in-the-middle attack if the VerifyHostKeyDNS     option is enabled (disabled by default).

    Details can be found in the Qualys advisory at     https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt

    For the stable distribution (bookworm), this problem has been fixed in     version 1:9.2p1-2+deb12u5.

    We recommend that you upgrade your openssh packages.

    For the detailed security status of openssh please refer to its security     tracker page at:
    https://security-tracker.debian.org/tracker/openssh

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

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

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

The remote Debian 11 host has packages installed that are affected by a vulnerability as referenced in the dla-4057 advisory.

    -------------------------------------------------------------------------     Debian LTS Advisory DLA-4057-1                debian-lts@lists.debian.org     https://www.debian.org/lts/security/                         Colin Watson     February 18, 2025                             https://wiki.debian.org/LTS
    -------------------------------------------------------------------------

    Package        : openssh     Version        : 1:8.4p1-5+deb11u4     CVE ID         : CVE-2025-26465

    The Qualys Threat Research Unit (TRU) discovered that the OpenSSH client     is vulnerable to a machine-in-the-middle attack if the VerifyHostKeyDNS     option is enabled (disabled by default).

    Details can be found in the Qualys advisory at     https://www.qualys.com/2025/02/18/openssh-mitm-dos.txt

    For Debian 11 bullseye, this problem has been fixed in version     1:8.4p1-5+deb11u4.

    We recommend that you upgrade your openssh packages.

    For the detailed security status of openssh please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/openssh

    Further information about Debian LTS security advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://wiki.debian.org/LTS     Attachment:
    signature.asc     Description: PGP signature

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

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

ID	Name	Product	Family	Severity
216579	Photon OS 4.0: Openssh PHSA-2025-4.0-0757	Nessus	PhotonOS Local Security Checks	medium
216524	Photon OS 3.0: Openssh PHSA-2025-3.0-0817	Nessus	PhotonOS Local Security Checks	medium
216523	Photon OS 5.0: Openssh PHSA-2025-5.0-0475	Nessus	PhotonOS Local Security Checks	medium
216476	OpenSSH < 9.9p2 MitM	Nessus	Misc.	medium
216453	SUSE SLED15 / SLES15 / openSUSE 15 Security Update : openssh (SUSE-SU-2025:0585-1)	Nessus	SuSE Local Security Checks	medium
216430	Ubuntu 16.04 LTS / 18.04 LTS : OpenSSH vulnerability (USN-7270-2)	Nessus	Ubuntu Local Security Checks	medium
216429	GLSA-202502-01 : OpenSSH: Multiple Vulnerabilities	Nessus	Gentoo Local Security Checks	medium
216428	Slackware Linux 15.0 / current openssh Multiple Vulnerabilities (SSA:2025-049-01)	Nessus	Slackware Local Security Checks	medium
216422	Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS / 24.10 : OpenSSH vulnerabilities (USN-7270-1)	Nessus	Ubuntu Local Security Checks	medium
216407	Debian dsa-5868 : openssh-client - security update	Nessus	Debian Local Security Checks	medium
216406	Debian dla-4057 : openssh-client - security update	Nessus	Debian Local Security Checks	medium

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CVE-2025-26465

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