Linux Distros Unpatched Vulnerability : CVE-2026-55990

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

include('compat.inc');

if (description)
{
  script_id(329537);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/07/25");

  script_cve_id("CVE-2026-55990");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-55990");

  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.

  - In NLnet Labs Unbound 1.7.0 up to and including 1.25.1, when the 'dnscrypt:' clause lists more 'dnscrypt-
    provider-cert:' files than there are matching 'dnscrypt-secret-key:' files, Unbound fills only the matched
    prefix and leaves the tail slots at the '0xdb' fill that libsodium's allocator writes into every
    allocation. Unbound would then iterate over the number of cert files, not the actual slots, so it walks
    into a slot with garbage data filled with '0xdb' bytes. Any unauthenticated client that sends one UDP
    datagram of  68 bytes whose first 8 bytes are '0xdb' to 'dnscrypt-port' will use that garbage entry which
    leads to a garbage dereference killing the server. This is a silent faulty configuration that goes
    unnoticed until triggered with the right client query. Unbound needs to be compiled with DNSCrypt support
    ('--enable-dnscrypt'). (CVE-2026-55990)

Note that Nessus relies on the presence of the package as reported by the vendor.");
  script_set_attribute(attribute:"see_also", value:"https://security-tracker.debian.org/tracker/CVE-2026-55990");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2026-55990");
  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:P/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:H/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-2026-55990");

  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:"2026/07/22");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/07/25");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:14.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:16.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:18.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:20.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:22.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:24.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:26.04:-:lts");
  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:"p-cpe:/a:canonical:ubuntu_linux:unbound");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:unbound");
  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/Debian Linux-11", "Host/OS/Debian Linux-12", "Host/OS/Debian Linux-13", "Host/OS/Debian Linux-14", "Host/OS/Ubuntu Linux-14.04", "Host/OS/Ubuntu Linux-16.04", "Host/OS/Ubuntu Linux-18.04", "Host/OS/Ubuntu Linux-20.04", "Host/OS/Ubuntu Linux-22.04", "Host/OS/Ubuntu Linux-24.04", "Host/OS/Ubuntu Linux-26.04");

  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/Debian/dpkg-l"))) 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": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Debian Linux-12": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "12",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Debian Linux-13": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "13",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Debian Linux-14": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-22.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "22.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-24.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "24.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-26.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "26.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-14.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound2"},
          {"reference": "python-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-16.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "16.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound2"},
          {"reference": "python-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-18.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "18.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound2"},
          {"reference": "python-unbound"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  },
  "Ubuntu Linux-20.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "20.04",
        "pkgs": [
          {"reference": "libunbound-dev"},
          {"reference": "libunbound8"},
          {"reference": "python-unbound"},
          {"reference": "python3-unbound"},
          {"reference": "unbound"},
          {"reference": "unbound-anchor"},
          {"reference": "unbound-host"}
        ]
      }
    ]
  }
};

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 third_party_support = get_kb_item('Host/OS/extended-third-party');
if (!empty_or_null(third_party_support)) {
    var third_party_vendors = distro_constraints_values['third_party'];
    if (!empty_or_null(third_party_vendors)) {
        var vendor;
        foreach vendor (third_party_vendors) {
            if (vendor == third_party_support) exit(0, 'A third party management patch is available for this vulnerability from ' + vendor + '.\n');
        }
    }
}

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');
}