nginx 0.9.x < 1.30.4 / 1.31.x < 1.31.3 Heap-based Buffer Overflow

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

include('compat.inc');

if (description)
{
  script_id(366466);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/10/16");

  script_cve_id("CVE-2026-42533");
  script_xref(name:"IAVA", value:"2026-A-0754");

  script_name(english:"nginx 0.9.x < 1.30.4 / 1.31.x < 1.31.3 Heap-based Buffer Overflow");

  script_set_attribute(attribute:"synopsis", value:
"The remote web server is affected by a heap-base buffer overflow vulnerability.");
  script_set_attribute(attribute:"description", value:
"According to its Sever response header, the installed version of nginx is 0.9.x prior to 1.30.4 or 1.31.x prior to
1.31.3. It is, therefore, affected by the following issue :

  - A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a
    string expression references the map's regex capture variables before referencing the map output variable.
    Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression
    under certain conditions. An unauthenticated attacker along with conditions beyond their control can
    exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the
    NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with
    Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This
    vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to
    possibly trigger a code execution. There is no control plane exposure; this is a data plane issue only.
    Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
    (CVE-2026-42533)

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://nginx.org/en/security_advisories.html");
  script_set_attribute(attribute:"see_also", value:"https://my.f5.com/manage/s/article/K000162097");
  script_set_attribute(attribute:"see_also", value:"https://www.cve.org/CVERecord?id=CVE-2026-42533");
  script_set_attribute(attribute:"solution", value:
"Upgrade to nginx 1.30.4 or 1.31.3 or later.");
  script_set_attribute(attribute:"agent", value:"unix");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:H/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:F/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:F/RL:O/RC:C");
  script_set_attribute(attribute:"cvss4_vector", value:"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N");
  script_set_attribute(attribute:"cvss4_threat_vector", value:"CVSS:4.0/E:P");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-42533");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/07/15");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/10/16");

  script_set_attribute(attribute:"potential_vulnerability", value:"true");
  script_set_attribute(attribute:"plugin_type", value:"combined");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:nginx:nginx");
  script_set_attribute(attribute:"stig_severity", value:"I");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Web Servers");

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

  script_dependencies("nginx_detect.nasl", "nginx_nix_installed.nbin");
  script_require_keys("Settings/ParanoidReport", "installed_sw/nginx");

  exit(0);
}

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

# requires a 'map' directive using specific regex (CVE-2026-42533)
if (report_paranoia < 2)
  audit(AUDIT_PARANOID);

var appname = 'nginx';
get_install_count(app_name:appname, exit_if_zero:TRUE);

var app_info = vcf::combined_get_app_info(app:appname);
vcf::check_granularity(app_info:app_info, sig_segments:3);

var constraints = [
  { 'min_version' : '0.9.6', 'fixed_version' : '1.30.4' },
  { 'min_version' : '1.31.0', 'fixed_version' : '1.31.3' }
];
vcf::check_version_and_report(
    app_info:app_info,
    constraints:constraints,
    severity:SECURITY_HOLE
);