Xen: Stale TLB Entry Ahead of Page Scrubbing (XSA-511)

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

include('compat.inc');

if (description)
{
  script_id(344803);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/09/11");

  script_cve_id("CVE-2026-79603");
  script_xref(name:"IAVB", value:"2026-B-0250");

  script_name(english:"Xen: Stale TLB Entry Ahead of Page Scrubbing (XSA-511)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Xen hypervisor installation is missing a security update.");
  script_set_attribute(attribute:"description", value:
"x86 PV guests can free memory pages while still keeping a stale TLB entry pointing to them. A TLB flush is only issued
by Xen (if needed) when the page is re-used. Since it's possible for the page to be scrubbed ahead of the TLB flush,
there's a window where a PV guest can modify an already scrubbed page.

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.xenproject.org/xsa/advisory-511.html");
  script_set_attribute(attribute:"solution", value:
"Apply the appropriate patch according to the vendor advisory.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:S/C:P/I:N/A:N");
  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_attribute(attribute:"cvss_score_source", value:"CVE-2026-79603");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/09/08");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/09/08");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/09/11");

  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) 2026 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('vcf.inc');
include('vcf_extras.inc');

var fixes;
var app = 'Xen Hypervisor';
var app_info = vcf::xen_hypervisor::get_app_info(app:app);
if (report_paranoia < 2) audit(AUDIT_PARANOID);

fixes['4.17']['fixed_ver']           = '4.17.7';
fixes['4.17']['fixed_ver_display']   = '4.17.7 (changeset d3b6291)';
fixes['4.17']['affected_ver_regex']  = "^4\.17([^0-9]|$)";
fixes['4.17']['affected_changesets'] = make_list("e275898", "439228f",
  "9373a59");

fixes['4.18']['fixed_ver']           = '4.18.6';
fixes['4.18']['fixed_ver_display']   = '4.18.6 (changeset 4351ad8)';
fixes['4.18']['affected_ver_regex']  = "^4\.18([^0-9]|$)";
fixes['4.18']['affected_changesets'] = make_list("f951c3a", "a5817d1",
  "c935589");

fixes['4.19']['fixed_ver']           = '4.19.6';
fixes['4.19']['fixed_ver_display']   = '4.19.6 (changeset 6dd2784)';
fixes['4.19']['affected_ver_regex']  = "^4\.19([^0-9]|$)";
fixes['4.19']['affected_changesets'] = make_list("aabdb18", "5dd29d6",
  "54ee7c5");

fixes['4.20']['fixed_ver']           = '4.20.5';
fixes['4.20']['fixed_ver_display']   = '4.20.5-pre (changeset bd0a1cf)';
fixes['4.20']['affected_ver_regex']  = "^4\.20([^0-9]|$)";
fixes['4.20']['affected_changesets'] = make_list("1514f28", "b26451e",
  "7b7f5be", "88c2d73", "d3eddf9", "ee3befc", "da5a214", "934897e",
  "2862edc");

fixes['4.21']['fixed_ver']           = '4.21.3';
fixes['4.21']['fixed_ver_display']   = '4.21.3-pre (changeset 391bc11)';
fixes['4.21']['affected_ver_regex']  = "^4\.21([^0-9]|$)";
fixes['4.21']['affected_changesets'] = make_list("e350834", "d9dbb24",
  "1cefa77", "21ef125", "cd91b44", "fc203d4", "6a78d0e", "1129f83",
  "9dccd42", "9113315");

vcf::xen_hypervisor::check_version_and_report(app_info:app_info, fixes:fixes, severity:SECURITY_WARNING);