Linux Distros Unpatched Vulnerability : CVE-2026-55653

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
##

include('compat.inc');

if (description)
{
  script_id(322159);
  script_version("1.2");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/06/23");

  script_cve_id("CVE-2026-55653");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-55653");

  script_set_attribute(attribute:"synopsis", value:
"The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be
patched.");
  script_set_attribute(attribute:"description", value:
"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 malicious SSH server can exploit a double free vulnerability in the Diffie-
    Hellman Group Exchange (DH-GEX) client path. This occurs during FIPS (Federal Information Processing
    Standards) mode known-group validation when the client processes attacker-controlled DH-GEX group
    parameters. Successful exploitation leads to client-side process termination, resulting in a Denial of
    Service (DoS). (CVE-2026-55653)

Note that Nessus relies on the presence of the package as reported by the vendor.");
  script_set_attribute(attribute:"see_also", value:"https://access.redhat.com/security/cve/cve-2026-55653");
  script_set_attribute(attribute:"see_also", value:"https://security-tracker.debian.org/tracker/CVE-2026-55653");
  script_set_attribute(attribute:"solution", value:
"There is no known solution at this time.");
  script_set_attribute(attribute:"agent", value:"unix");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:U/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:U/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-55653");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");
  script_set_attribute(attribute:"vendor_unpatched", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/06/23");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/06/23");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:centos:centos:7");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:centos:centos:8");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:11.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:12.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:13.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:14.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:redhat:enterprise_linux:10");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:redhat:enterprise_linux:6");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:redhat:enterprise_linux:7");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:redhat:enterprise_linux:8");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:redhat:enterprise_linux:9");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-askpass");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-cavs");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-clients");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-keycat");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-keysign");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-ldap");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-server");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:openssh-server-sysvinit");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:centos:centos:pam_ssh_agent_auth");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:openssh");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-askpass");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-cavs");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-clients");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-keycat");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-keysign");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-ldap");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-server");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:openssh-server-sysvinit");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:redhat:enterprise_linux:pam_ssh_agent_auth");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Misc.");

  script_copyright(english:"This script is Copyright (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info2.nasl", "set_linux_os_id.nasl");
  script_require_keys("Host/cpu", "Host/local_checks_enabled", "global_settings/vendor_unpatched", "Host/OS/identifier");
  script_require_ports("Host/OS/CentOS Linux-7", "Host/OS/CentOS Linux-8", "Host/OS/Debian Linux-11", "Host/OS/Debian Linux-12", "Host/OS/Debian Linux-13", "Host/OS/Debian Linux-14", "Host/OS/Red Hat Enterprise Linux-10", "Host/OS/Red Hat Enterprise Linux-6", "Host/OS/Red Hat Enterprise Linux-7", "Host/OS/Red Hat Enterprise Linux-8", "Host/OS/Red Hat Enterprise Linux-9");

  exit(0);
}

if (!get_kb_item("global_settings/vendor_unpatched")) exit(0, "Unpatched Vulnerabilities Detection not active.");
if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (empty_or_null(get_one_kb_item("Host/CentOS/rpm-list")) && empty_or_null(get_one_kb_item("Host/Debian/dpkg-l")) && empty_or_null(get_one_kb_item("Host/RedHat/rpm-list"))) audit(AUDIT_PACKAGE_LIST_MISSING);

include('linux_unpatched.inc');

var distro_constraints_array = {
  "Debian Linux-11": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "11",
        "pkgs": [
          {"reference": "openssh-client"},
          {"reference": "openssh-client-udeb"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-udeb"},
          {"reference": "openssh-sftp-server"},
          {"reference": "openssh-tests"},
          {"reference": "ssh"},
          {"reference": "ssh-askpass-gnome"}
        ]
      }
    ]
  },
  "Debian Linux-12": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "12",
        "pkgs": [
          {"reference": "openssh-client"},
          {"reference": "openssh-client-udeb"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-udeb"},
          {"reference": "openssh-sftp-server"},
          {"reference": "openssh-tests"},
          {"reference": "ssh"},
          {"reference": "ssh-askpass-gnome"}
        ]
      }
    ]
  },
  "Debian Linux-13": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "13",
        "pkgs": [
          {"reference": "openssh-client"},
          {"reference": "openssh-client-gssapi"},
          {"reference": "openssh-client-udeb"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-gssapi"},
          {"reference": "openssh-server-udeb"},
          {"reference": "openssh-sftp-server"},
          {"reference": "openssh-tests"},
          {"reference": "ssh"},
          {"reference": "ssh-askpass-gnome"}
        ]
      }
    ]
  },
  "Debian Linux-14": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14",
        "pkgs": [
          {"reference": "openssh-client"},
          {"reference": "openssh-client-gssapi"},
          {"reference": "openssh-client-udeb"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-gssapi"},
          {"reference": "openssh-server-udeb"},
          {"reference": "openssh-sftp-server"},
          {"reference": "openssh-tests"},
          {"reference": "ssh"},
          {"reference": "ssh-askpass-gnome"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-10": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "10",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-keysign"},
          {"reference": "openssh-server"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-6": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "6",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-ldap"},
          {"reference": "openssh-server"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  },
  "CentOS Linux-7": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "7",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-cavs"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-ldap"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-sysvinit"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-7": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "7",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-cavs"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-ldap"},
          {"reference": "openssh-server"},
          {"reference": "openssh-server-sysvinit"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  },
  "CentOS Linux-8": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "8",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-cavs"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-ldap"},
          {"reference": "openssh-server"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-8": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "8",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-cavs"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-ldap"},
          {"reference": "openssh-server"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-9": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "9",
        "pkgs": [
          {"reference": "openssh"},
          {"reference": "openssh-askpass"},
          {"reference": "openssh-clients"},
          {"reference": "openssh-keycat"},
          {"reference": "openssh-server"},
          {"reference": "pam_ssh_agent_auth"}
        ]
      }
    ]
  }
};

var distro_constraints_values = linux_unpatched::get_distro_constraints(distro_constraints_arr:distro_constraints_array);
if (empty_or_null(distro_constraints_values)) audit(AUDIT_HOST_NOT, 'affected');
var report = linux_unpatched::check_unpatched_constraints(distro_constraints_values:distro_constraints_values);

if (!empty_or_null(report))
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : report
  );
  exit(0);
}
else
{
  audit(AUDIT_HOST_NOT, 'affected');
}