Xen Project VCPUOP_initialise DoS (XSA-296)

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

include("compat.inc");

if (description)
{
  script_id(130759);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/07/10");

  script_cve_id("CVE-2019-18420");
  script_xref(name:"IAVB", value:"2019-B-0084-S");

  script_name(english:"Xen Project VCPUOP_initialise DoS (XSA-296)");
  script_summary(english:"Checks 'xl info' output for the Xen hypervisor version.");

  script_set_attribute(attribute:"synopsis", value:
"The remote Xen hypervisor installation is missing a security update.");
  script_set_attribute(attribute:"description", value:
"According to its self-reported version number, the Xen hypervisor installed on
the remote host is affected by a denial of service vulnerability due to poor
handling of an invalid format string in 'hypercall_create_continuation()'. This
function can be reached via a long-running 'VCPUOP_initialise' hypercall. This
vulnerability may allow an attacker to preform a guest-to-host denial of
service attack causing the Xen hypervisor to crash. Only x86 PV guests are
exploitable.

Note that Nessus has checked the changeset versions based on the xen.git change
log. Nessus did not check guest hardware configurations or if patches were
applied manually to the source code before a recompile and reinstall.");
  script_set_attribute(attribute:"see_also", value:"https://xenbits.xen.org/xsa/advisory-296.html");
  script_set_attribute(attribute:"see_also", value:"https://xenbits.xen.org/gitweb/?p=xen.git;a=summary");
  script_set_attribute(attribute:"solution", value:
"Apply the appropriate patch according to the vendor advisory.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:S/C:N/I:N/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2019-18420");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");

  script_set_attribute(attribute:"vuln_publication_date", value:"2019/10/31");
  script_set_attribute(attribute:"patch_publication_date", value:"2019/10/31");
  script_set_attribute(attribute:"plugin_publication_date", value:"2019/11/08");

  script_set_attribute(attribute:"potential_vulnerability", value:"true");
  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:xen:xen");
  script_set_attribute(attribute:"stig_severity", value:"I");
  script_end_attributes();

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

  script_copyright(english:"This script is Copyright (C) 2019-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("xen_server_detect.nbin");
  script_require_keys("installed_sw/Xen Hypervisor", "Settings/ParanoidReport");

  exit(0);
}

include("audit.inc");
include("global_settings.inc");
include("install_func.inc");
include("misc_func.inc");

app_name = "Xen Hypervisor";
install  = get_single_install(app_name:app_name);
if (report_paranoia < 2) audit(AUDIT_PARANOID);

version         = install['version'];
display_version = install['display_version'];
path            = install['path'];
managed_status  = install['Managed status'];
changeset       = install['Changeset'];

if (!empty_or_null(changeset))
  display_version += " (changeset " + changeset + ")";

# Installations that are vendor-managed are handled by OS-specific local package checks
if (managed_status == "managed")
  audit(AUDIT_INST_PATH_NOT_VULN, app_name, display_version, path);

fixes['4.8']['fixed_ver']           = '4.8.5';
fixes['4.8']['fixed_ver_display']   = '4.8.5';
fixes['4.8']['affected_ver_regex']  = '^4\\.8\\.';

fixes['4.9']['fixed_ver']           = '4.9.4';
fixes['4.9']['fixed_ver_display']   = '4.9.4';
fixes['4.9']['affected_ver_regex']  = '^4\\.9\\.';

fixes['4.10']['fixed_ver']           = '4.10.4';
fixes['4.10']['fixed_ver_display']   = '4.10.4';
fixes['4.10']['affected_ver_regex']  = '^4\\.10\\.';

fixes['4.11']['fixed_ver']           = '4.11.3';
fixes['4.11']['fixed_ver_display']   = '4.11.3-pre';
fixes['4.11']['affected_ver_regex']  = '^4\\.11\\.';

fixes['4.12']['fixed_ver']           = '4.12.2';
fixes['4.12']['fixed_ver_display']   = '4.12.2-pre';
fixes['4.12']['affected_ver_regex']  = '^4\\.12\\.';

fix = NULL;
foreach ver_branch (keys(fixes))
{
  if (version =~ fixes[ver_branch]['affected_ver_regex'])
  {
    ret = ver_compare(ver:version, fix:fixes[ver_branch]['fixed_ver']);
    if (ret < 0)
      fix = fixes[ver_branch]['fixed_ver_display'];
    else if (ret == 0)
    {
      if (empty_or_null(changeset) || empty_or_null(fixes[ver_branch]['affected_changesets']))
        fix = fixes[ver_branch]['fixed_ver_display'];
      else
        foreach affected_changeset (fixes[ver_branch]['affected_changesets'])
          if (changeset == affected_changeset)
            fix = fixes[ver_branch]['fixed_ver_display'];
    }
  }
}

if (empty_or_null(fix))
  audit(AUDIT_INST_PATH_NOT_VULN, app_name, display_version, path);

items  = make_array(
  "Installed version", display_version,
  "Fixed version", fix,
  "Path", path
);

order  = make_list("Path", "Installed version", "Fixed version");
report = report_items_str(report_items:items, ordered_fields:order) + '\n';

security_report_v4(port:0, extra:report, severity:SECURITY_WARNING);