Linux Distros Unpatched Vulnerability : CVE-2021-20257

##
# (C) Tenable, Inc.
##

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if (description)
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  script_id(223625);
  script_version("1.5");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/06/10");

  script_cve_id("CVE-2021-20257");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2021-20257");

  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.

  - An infinite loop flaw was found in the e1000 NIC emulator of the QEMU. This issue occurs while processing
    transmits (tx) descriptors in process_tx_desc if various descriptor fields are initialized with invalid
    values. This flaw allows a guest to consume CPU cycles on the host, resulting in a denial of service. The
    highest threat from this vulnerability is to system availability. (CVE-2021-20257)

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-2021-20257");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2021-20257");
  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:L/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:L/AC:L/PR:L/UI:N/S:C/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-2021-20257");

  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:"2020/12/03");
  script_set_attribute(attribute:"plugin_publication_date", value:"2025/03/04");

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}

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 = {
  "CentOS Linux-8": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "8",
        "pkgs": [
          {"reference": "qemu-guest-agent"},
          {"reference": "qemu-img"},
          {"reference": "qemu-kiwi"},
          {"reference": "qemu-kvm"},
          {"reference": "qemu-kvm-block-curl"},
          {"reference": "qemu-kvm-block-gluster"},
          {"reference": "qemu-kvm-block-iscsi"},
          {"reference": "qemu-kvm-block-rbd"},
          {"reference": "qemu-kvm-block-ssh"},
          {"reference": "qemu-kvm-common"},
          {"reference": "qemu-kvm-core"},
          {"reference": "qemu-kvm-docs"},
          {"reference": "qemu-kvm-hw-usbredir"},
          {"reference": "qemu-kvm-tests"},
          {"reference": "qemu-kvm-ui-opengl"},
          {"reference": "qemu-kvm-ui-spice"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-8": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "8",
        "pkgs": [
          {"reference": "qemu-guest-agent"},
          {"reference": "qemu-img"},
          {"reference": "qemu-kiwi"},
          {"reference": "qemu-kvm"},
          {"reference": "qemu-kvm-block-curl"},
          {"reference": "qemu-kvm-block-gluster"},
          {"reference": "qemu-kvm-block-iscsi"},
          {"reference": "qemu-kvm-block-rbd"},
          {"reference": "qemu-kvm-block-ssh"},
          {"reference": "qemu-kvm-common"},
          {"reference": "qemu-kvm-core"},
          {"reference": "qemu-kvm-docs"},
          {"reference": "qemu-kvm-hw-usbredir"},
          {"reference": "qemu-kvm-tests"},
          {"reference": "qemu-kvm-ui-opengl"},
          {"reference": "qemu-kvm-ui-spice"}
        ]
      }
    ]
  },
  "CentOS Linux-7": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "7",
        "pkgs": [
          {"reference": "libcacard"},
          {"reference": "libcacard-devel"},
          {"reference": "libcacard-tools"},
          {"reference": "qemu-guest-agent"},
          {"reference": "qemu-img"},
          {"reference": "qemu-img-rhev"},
          {"reference": "qemu-kvm"},
          {"reference": "qemu-kvm-common"},
          {"reference": "qemu-kvm-common-rhev"},
          {"reference": "qemu-kvm-rhev"},
          {"reference": "qemu-kvm-tools"},
          {"reference": "qemu-kvm-tools-rhev"}
        ]
      }
    ]
  },
  "Red Hat Enterprise Linux-7": {
    "package_manager": "rpm-list",
    "constraints": [
      {
        "release": "7",
        "pkgs": [
          {"reference": "libcacard"},
          {"reference": "libcacard-devel"},
          {"reference": "libcacard-tools"},
          {"reference": "qemu-guest-agent"},
          {"reference": "qemu-img"},
          {"reference": "qemu-img-rhev"},
          {"reference": "qemu-kvm"},
          {"reference": "qemu-kvm-common"},
          {"reference": "qemu-kvm-common-rhev"},
          {"reference": "qemu-kvm-rhev"},
          {"reference": "qemu-kvm-tools"},
          {"reference": "qemu-kvm-tools-rhev"}
        ]
      }
    ]
  }
};

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_NOTE,
      extra      : report
  );
  exit(0);
}
else
{
  audit(AUDIT_HOST_NOT, 'affected');
}