Linux Distros Unpatched Vulnerability : CVE-2021-28689

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

include('compat.inc');

if (description)
{
  script_id(232305);
  script_version("1.8");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/05/21");

  script_cve_id("CVE-2021-28689");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2021-28689");

  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.

  - x86: Speculative vulnerabilities with bare (non-shim) 32-bit PV guests 32-bit x86 PV guest kernels run in
    ring 1. At the time when Xen was developed, this area of the i386 architecture was rarely used, which is
    why Xen was able to use it to implement paravirtualisation, Xen's novel approach to virtualization. In
    AMD64, Xen had to use a different implementation approach, so Xen does not use ring 1 to support 64-bit
    guests. With the focus now being on 64-bit systems, and the availability of explicit hardware support for
    virtualization, fixing speculation issues in ring 1 is not a priority for processor companies. Indirect
    Branch Restricted Speculation (IBRS) is an architectural x86 extension put together to combat speculative
    execution sidechannel attacks, including Spectre v2. It was retrofitted in microcode to existing CPUs. For
    more details on Spectre v2, see: http://xenbits.xen.org/xsa/advisory-254.html However, IBRS does not
    architecturally protect ring 0 from predictions learnt in ring 1. For more details, see:
    https://software.intel.com/security-software-guidance/deep-dives/deep-dive-indirect-branch-restricted-
    speculation Similar situations may exist with other mitigations for other kinds of speculative execution
    attacks. The situation is quite likely to be similar for speculative execution attacks which have yet to
    be discovered, disclosed, or mitigated. (CVE-2021-28689)

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-2021-28689");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2021-28689");
  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:P/I:N/A:N");
  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:U/C:H/I:N/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:U/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2021-28689");

  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:"2021/02/18");
  script_set_attribute(attribute:"plugin_publication_date", value:"2025/03/10");

  script_set_attribute(attribute:"plugin_type", value:"local");
  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:25.04");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:25.10");
  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:xen");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:xen");
  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) 2025-2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("set_linux_os_id.nasl", "ssh_get_info2.nasl");
  script_require_keys("Host/OS/identifier", "Host/cpu", "Host/local_checks_enabled", "global_settings/vendor_unpatched");
  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-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-25.04", "Host/OS/Ubuntu Linux-25.10");

  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-12": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "12",
        "pkgs": [
          {"reference": "libxen-dev"},
          {"reference": "libxencall1"},
          {"reference": "libxendevicemodel1"},
          {"reference": "libxenevtchn1"},
          {"reference": "libxenforeignmemory1"},
          {"reference": "libxengnttab1"},
          {"reference": "libxenhypfs1"},
          {"reference": "libxenmisc4.17"},
          {"reference": "libxenstore4"},
          {"reference": "libxentoolcore1"},
          {"reference": "libxentoollog1"},
          {"reference": "xen-doc"},
          {"reference": "xen-hypervisor-4.17-amd64"},
          {"reference": "xen-hypervisor-4.17-amd64-dbg"},
          {"reference": "xen-hypervisor-4.17-arm64"},
          {"reference": "xen-hypervisor-4.17-arm64-dbg"},
          {"reference": "xen-hypervisor-4.17-armhf"},
          {"reference": "xen-hypervisor-4.17-armhf-dbg"},
          {"reference": "xen-hypervisor-common"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-system-armhf"},
          {"reference": "xen-utils-4.17"},
          {"reference": "xen-utils-4.17-dbg"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Debian Linux-11": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "11",
        "pkgs": [
          {"reference": "libxen-dev"},
          {"reference": "libxencall1"},
          {"reference": "libxendevicemodel1"},
          {"reference": "libxenevtchn1"},
          {"reference": "libxenforeignmemory1"},
          {"reference": "libxengnttab1"},
          {"reference": "libxenhypfs1"},
          {"reference": "libxenmisc4.14"},
          {"reference": "libxenstore3.0"},
          {"reference": "libxentoolcore1"},
          {"reference": "libxentoollog1"},
          {"reference": "xen-doc"},
          {"reference": "xen-hypervisor-4.14-amd64"},
          {"reference": "xen-hypervisor-4.14-arm64"},
          {"reference": "xen-hypervisor-4.14-armhf"},
          {"reference": "xen-hypervisor-common"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-system-armhf"},
          {"reference": "xen-utils-4.14"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Debian Linux-13": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "13",
        "pkgs": [
          {"reference": "libxen-dev"},
          {"reference": "libxencall1"},
          {"reference": "libxendevicemodel1"},
          {"reference": "libxenevtchn1"},
          {"reference": "libxenforeignmemory1"},
          {"reference": "libxengnttab1"},
          {"reference": "libxenhypfs1"},
          {"reference": "libxenmisc4.20"},
          {"reference": "libxenstore4"},
          {"reference": "libxentoolcore1"},
          {"reference": "libxentoollog1"},
          {"reference": "xen-doc"},
          {"reference": "xen-hypervisor-4.20-amd64"},
          {"reference": "xen-hypervisor-4.20-amd64-dbg"},
          {"reference": "xen-hypervisor-4.20-arm64"},
          {"reference": "xen-hypervisor-4.20-arm64-dbg"},
          {"reference": "xen-hypervisor-common"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-utils-4.20"},
          {"reference": "xen-utils-4.20-dbg"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Debian Linux-14": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14",
        "pkgs": [
          {"reference": "libxen-dev"},
          {"reference": "libxencall1"},
          {"reference": "libxendevicemodel1"},
          {"reference": "libxenevtchn1"},
          {"reference": "libxenforeignmemory1"},
          {"reference": "libxengnttab1"},
          {"reference": "libxenhypfs1"},
          {"reference": "libxenmisc4.20"},
          {"reference": "libxenstore4"},
          {"reference": "libxentoolcore1"},
          {"reference": "libxentoollog1"},
          {"reference": "xen-doc"},
          {"reference": "xen-hypervisor-4.20-amd64"},
          {"reference": "xen-hypervisor-4.20-amd64-dbg"},
          {"reference": "xen-hypervisor-4.20-arm64"},
          {"reference": "xen-hypervisor-4.20-arm64-dbg"},
          {"reference": "xen-hypervisor-common"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-utils-4.20"},
          {"reference": "xen-utils-4.20-dbg"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Ubuntu Linux-16.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "16.04",
        "pkgs": [
          {"reference": "libxen-4.6"},
          {"reference": "libxen-dev"},
          {"reference": "libxenstore3.0"},
          {"reference": "xen-hypervisor-4.4-amd64"},
          {"reference": "xen-hypervisor-4.4-arm64"},
          {"reference": "xen-hypervisor-4.4-armhf"},
          {"reference": "xen-hypervisor-4.5-amd64"},
          {"reference": "xen-hypervisor-4.5-arm64"},
          {"reference": "xen-hypervisor-4.5-armhf"},
          {"reference": "xen-hypervisor-4.6-amd64"},
          {"reference": "xen-hypervisor-4.6-arm64"},
          {"reference": "xen-hypervisor-4.6-armhf"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-system-armhf"},
          {"reference": "xen-utils-4.6"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Ubuntu Linux-18.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "18.04",
        "pkgs": [
          {"reference": "libxen-4.9"},
          {"reference": "libxen-dev"},
          {"reference": "libxenstore3.0"},
          {"reference": "xen-hypervisor-4.6-amd64"},
          {"reference": "xen-hypervisor-4.6-arm64"},
          {"reference": "xen-hypervisor-4.6-armhf"},
          {"reference": "xen-hypervisor-4.7-amd64"},
          {"reference": "xen-hypervisor-4.7-arm64"},
          {"reference": "xen-hypervisor-4.7-armhf"},
          {"reference": "xen-hypervisor-4.8-amd64"},
          {"reference": "xen-hypervisor-4.8-arm64"},
          {"reference": "xen-hypervisor-4.8-armhf"},
          {"reference": "xen-hypervisor-4.9-amd64"},
          {"reference": "xen-hypervisor-4.9-arm64"},
          {"reference": "xen-hypervisor-4.9-armhf"},
          {"reference": "xen-system-amd64"},
          {"reference": "xen-system-arm64"},
          {"reference": "xen-system-armhf"},
          {"reference": "xen-utils-4.9"},
          {"reference": "xen-utils-common"},
          {"reference": "xenstore-utils"}
        ]
      }
    ]
  },
  "Ubuntu Linux-20.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "20.04",
        "pkgs": [
          {"reference": "xen"}
        ]
      }
    ]
  },
  "Ubuntu Linux-22.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "22.04",
        "pkgs": [
          {"reference": "xen"}
        ]
      }
    ]
  },
  "Ubuntu Linux-24.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "24.04",
        "pkgs": [
          {"reference": "xen"}
        ]
      }
    ]
  },
  "Ubuntu Linux-25.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "25.04",
        "pkgs": [
          {"reference": "xen"}
        ]
      }
    ]
  },
  "Ubuntu Linux-25.10": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "25.10",
        "pkgs": [
          {"reference": "xen"}
        ]
      }
    ]
  }
};

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');
}