Security Update for Windows Defender (May 2026) (CVE-2026-41091)

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

include('compat.inc');

if (description)
{
  script_id(316462);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/06/16");

  script_cve_id("CVE-2026-41091");
  script_xref(name:"CISA-KNOWN-EXPLOITED", value:"2026/06/03");

  script_name(english:"Security Update for Windows Defender (May 2026) (CVE-2026-41091)");

  script_set_attribute(attribute:"synopsis", value:
"An antimalware application installed on the remote host is affected by a privilege escalation vulnerability.");
  script_set_attribute(attribute:"description", value:
"The Malware Protection Engine version of Microsoft Windows Defender installed on the remote Windows host
is prior to 1.1.26040.8. It is, therefore, affected by a privilege escalation vulnerability:

  - Improper link resolution before file access ('link following') in Microsoft Defender allows an
    authorized attacker to elevate privileges locally. (CVE-2026-41091)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported
version number.");
  # https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-41091
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?b74f81ae");
  script_set_attribute(attribute:"solution", value:
"Enable automatic updates to update the malware engine for the relevant antimalware applications. Refer to Knowledge Base
Article 2510781 for information on how to verify that MMPE has been updated.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:S/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:H/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:H/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-41091");

  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");
  script_set_attribute(attribute:"exploited_by_malware", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/05/19");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/05/19");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/05/22");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:microsoft:windows");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:microsoft:windows_defender");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Windows : Microsoft Bulletins");

  script_copyright(english:"This script is Copyright (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("microsoft_windows_defender_win_installed.nbin");
  script_require_keys("installed_sw/Windows Defender");

  exit(0);
}

include('vcf.inc');
include('vcf_extras.inc');

var app = 'Windows Defender';

var app_info = vcf::get_app_info(app:app, win_local:TRUE);

if (!isnull(app_info['Disabled']))
  exit(0, 'Windows Defender is disabled.');

if (isnull(app_info['Engine Version']))
  exit(0, 'Unable to get the Malware Engine Version.');

var constraints = [{'fixed_version':'1.1.26040.8'}];

vcf::av_checks::check_version_and_report(app_info:app_info, constraints:constraints, severity:SECURITY_WARNING, check:'Engine Version');