Xen Migrating Timers Race condition DoS (XSA-336)

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

include('compat.inc');

if (description)
{
  script_id(141836);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/11/13");

  script_cve_id("CVE-2020-25604");
  script_xref(name:"IAVB", value:"2020-B-0056-S");

  script_name(english:"Xen Migrating Timers Race condition DoS (XSA-336)");

  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 (DoS) vulnerability. When migrating timers of x86 HVM guests between its vCPU-s, the locking model used
allows for a second vCPU of the same guest also operating on the timers to release a lock that it didn't acquire. An 
attacker can exploit this issue to crash the hypervisor and cause a DoS condition.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version   
number.");
  script_set_attribute(attribute:"see_also", value:"https://xenbits.xen.org/xsa/advisory-336.html");
  script_set_attribute(attribute:"solution", value:
"Apply the appropriate patch according to the vendor advisory.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:M/Au:N/C:N/I:N/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:H/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-2020-25604");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2020/09/22");
  script_set_attribute(attribute:"patch_publication_date", value:"2020/09/22");
  script_set_attribute(attribute:"plugin_publication_date", value:"2020/10/23");

  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) 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('install_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['4.10']['fixed_ver']           = '4.10.4';
fixes['4.10']['fixed_ver_display']   = '4.10.4 (changeset 635ae12)';
fixes['4.10']['affected_ver_regex']  = "^4\.10\.";
fixes['4.10']['affected_changesets'] = make_list('3d14937', '4218b74',
  '93be943', '4418841', 'd9c67d3', '8976bab', '388e303', '0b0a155',
  '9df4399', 'fd57038', 'a9bda69', 'a380168', 'c1a4914', '6261a06',
  'fd6e49e', 'bd20589', 'ce05683', '934d6e1', '6e636f2', 'dfc0b23',
  '2f83654', 'bf467cc', '6df4d40', 'e20bb58', 'a1a9b05', 'afca67f',
  'b922c44', 'b413732', '3d60903', 'b01c84e', '1e722e6', '59cf3a0',
  'fabfce8', 'a4dd2fe', '6e63a6f', '24d62e1', 'cbedabf', '38e589d',
  'a91b8fc', '3e0c316', '49a5d6e', '6cb1cb9', 'ba2776a', '9d143e8',
  'fe8dab3', '07e546e', 'fefa5f9', 'c9f9ff7', '406d40d', 'e489955',
  '37139f1', 'fde09cb', '804ba02', 'e8c3971', 'a8c4293', 'aa40452',
  '1da3dab', 'e5632c4', '902e72d', '6a14610', 'ea815b2', '13ad331',
  '61b75d9', 'e70e7bf', 'e966e2e', 'dfa16a1', 'a71e199', 'c98be9e',
  'a548e10', 'd3c0e84', '53b1572', '7203f9a', '6d1659d', 'a782173',
  '24e90db', '0824bc6', 'e6f3135', '3131bf9');

fixes['4.11']['fixed_ver']           = '4.11.4';
fixes['4.11']['fixed_ver_display']   = '4.11.4 (changeset 2fe163d)';
fixes['4.11']['affected_ver_regex']  = "^4\.11\.";
fixes['4.11']['affected_changesets'] = make_list('2031bd3', '7bf4983',
  '7129b9e', 'ddaaccb', 'e6ddf4a', 'f2bc74c', 'd623658', '37c853a',
  '8bf72ea', '2d11e6d', '4ed0007', '7def72c', '18be3aa', 'a3a392e',
  'e96cdba', '2b77729', '9be7992', 'b8d476a', '1c751c4', '7dd2ac3',
  'a58bba2', '7d8fa6a', '4777208', '48e8564', '2efca7e', 'afe82f5',
  'e84b634', '96a8b5b');

fixes['4.12']['fixed_ver']           = '4.12.4';
fixes['4.12']['fixed_ver_display']   = '4.12.4-pre (changeset 1dfd2e2)';
fixes['4.12']['affected_ver_regex']  = "^4\.12\.";
fixes['4.12']['affected_changesets'] = make_list('76a0760', 'd28c52e',
  '8b8fff2', '320e7a7', '0446e3d', 'a81e655', 'caebaf3', '76d9349',
  '81564c4', 'ff79981', '3186568', '40e0cf8', 'fbf016f', '8c1c3e7',
  '5bd49ca', 'e0bd899', 'c481b9f', '1336ca1', 'dca9cc7', '07fd5d3',
  '85ce36d', 'df9a0ad', '7cce3f2', '43258ce', 'a1aae54', 'df11056',
  '19e0bbb', 'd96c0f1', '653811e', '26072a5', 'b292255', '38dc269',
  '5733de6', 'd69f305', '8faa45e', '731bdaf', 'ec57b9a', 'a634229',
  '050fe48', '436ec68', '96e8aba', '7cdc0cf', 'd937532', '7641573',
  '7eed533', '74a1230', '946113a', '6182e5d', 'ad20170', '218a19b',
  'aca68b9', '1f581f9', '4969f34', 'ed44947', '2eb277e', 'b3af150',
  'f769c99', 'bcdaffc', '2b10a32', 'a022f36', 'dd49ddf', 'bc775d0', 'be5c240');

fixes['4.13']['fixed_ver']           = '4.13.2';
fixes['4.13']['fixed_ver_display']   = '4.13.2-pre (changeset f27980a)';
fixes['4.13']['affected_ver_regex']  = "^4\.13\.";
fixes['4.13']['affected_changesets'] = make_list('b7fcbe0', '42fcdd4',
  '286b353', 'b980319', 'aa1d9a7', 'bd63ab5', '4fb1ad7', '4a0c174',
  '6ef4dad', 'c663fa5', '761e8df', '6469039', 'b908343', 'ac4ec48',
  'a7f0434', '0861885', '9b367b2', 'e182965', 'befa216', 'e9e72fb',
  'b67bb90', 'fff1874', 'ec972cb', 'd967a2b', '665f5c1', 'ddb6fd3',
  '378321b', '572e349', '0c8c10d', '493e143', '8b9be8f', 'f1055a2',
  '005d5ea', '1c7a98c', '2b34d8c', '56e117f', '7a76deb', '3e41b72',
  '9f7e8ba', 'cdd8f95', 'a9d46ba', '05ba427', '780d376', '31c5d84',
  '27d4f1a', '11ea967', '53bafb5', 'b4afe05', '74ce65c', '0243559',
  '8ad99de', 'ea7e8d2', '350aaca', 'c3eea2c', '0523225', '672976c',
  'a6f2080', 'c437e06', '0a85f84', '85ac008', '7f6b66d', '04aedf4',
  'f2ad77b', 'd61fef6', 'eccc242', '6bfb364', 'bdddd33', '7d57caa',
  'd74eb10', '9eec3ee', 'd112db3', '333519f');

fixes['4.14']['fixed_ver']           = '4.14.1';
fixes['4.14']['fixed_ver_display']   = '4.14.1-pre (changeset 0bc4177)';
fixes['4.14']['affected_ver_regex']  = "^4\.14\.";
fixes['4.14']['affected_changesets'] = make_list('5ad3152', 'fc8200a',
  '5eab5f0', 'b04d673', '28855eb', '174be04', '158c3bd', '3535f23',
  'de7e543', '483b43c', '431d52a', 'ceafff7', '369e7a3', '98aa6ea',
  '80dec06', '5482c28', 'edf5b86', 'eca6d5e', 'c3a0fc2', '864d570',
  'afed8e4', 'a5dab0a', 'b8c3e33', 'f836759');

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))
        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_NOTE);