Mattermost Server 11.4.x <= 11.4.3 / 11.5.x <= 11.5.1 Origin Validation Error (MMSA-2026-00636)

#%NASL_MIN_LEVEL 80900

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

include('compat.inc');

if (description)
{
  script_id(316491);
  script_version("1.2");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/05/25");

  script_cve_id("CVE-2026-6339");
  script_xref(name:"IAVA", value:"2026-A-0492");

  script_name(english:"Mattermost Server 11.4.x <= 11.4.3 / 11.5.x <= 11.5.1 Origin Validation Error (MMSA-2026-00636)");

  script_set_attribute(attribute:"synopsis", value:
"The remote host is affected by an origin validation vulnerability.");
  script_set_attribute(attribute:"description", value:
"The version of Mattermost Server installed on the remote host is affected by a vulnerability as referenced in the
MMSA-2026-00636 advisory.

  - Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on
    the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a
    burn-on-read message without recipient consent via a crafted Markdown image tag. Mattermost Advisory ID:
    MMSA-2026-00636. (CVE-2026-6339)

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://mattermost.com/security-updates/");
  script_set_attribute(attribute:"solution", value:
"Upgrade to Mattermost Server version 11.4.4, 11.5.2, 11.6.0 or later.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:S/C:P/I:N/A:N");
  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:L/I:N/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-6339");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/04/15");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/04/15");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/05/22");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:mattermost:mattermost_server");
  script_set_attribute(attribute:"stig_severity", value:"I");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"CGI abuses");

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

  script_dependencies("mattermost_server_detect.nbin");
  script_require_keys("installed_sw/Mattermost Server");

  exit(0);
}

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

var port = get_http_port(default:80);

var app_info = vcf::get_app_info(app:'Mattermost Server', port:port, webapp:true);

var constraints = [
  { 'min_version' : '11.4.0', 'fixed_version' : '11.4.4' },
  { 'min_version' : '11.5.0', 'fixed_version' : '11.5.2', 'fixed_display' : '11.5.2 / 11.6.0' }
];

vcf::check_version_and_report(
  app_info:app_info,
  constraints:constraints,
  severity:SECURITY_WARNING
);