CentOS Linux 7 [TuxCare] Security Update: xorg-x11-server-Xdmx / xorg-x11-server-Xephyr / etc Multiple Vulnerabilities (CENTOS7:CLSA-2026:1788424564)

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

include('compat.inc');

if (description)
{
  script_id(352163);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/09/30");

  script_cve_id(
    "CVE-2026-50257",
    "CVE-2026-50258",
    "CVE-2026-50259",
    "CVE-2026-50260",
    "CVE-2026-50261"
  );
  script_xref(name:"CLSA", value:"2026:1788424564");

  script_name(english:"CentOS Linux 7 [TuxCare] Security Update: xorg-x11-server-Xdmx / xorg-x11-server-Xephyr / etc Multiple Vulnerabilities (CENTOS7:CLSA-2026:1788424564)");

  script_set_attribute(attribute:"synopsis", value:
"The CentOS Linux host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The CentOS Linux 7 host has packages installed that are affected by multiple vulnerabilities as referenced in the
TuxCare CENTOS7:CLSA-2026:1788424564 advisory.

  - A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A client that
    sets up multiple fence triggers can trigger a use-after-free function pointer call. An attacker would
    connect to the X server to set up a fence and await that fence, then a second X connection destroys the
    fence, causing the use-after-free. This may be used to crash the server, or for privilege escalation if
    the X server runs as root. (CVE-2026-50257)

  - A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple
    stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non-
    canonical key types to XkbMaxShiftLevel. A client can change key types to excessive shift levels and
    trigger stack overflows. This is caused by an incomplete fix of CVE-2025-26597. This may be used to crash
    the server, or for privilege escalation if the X server runs as root. (CVE-2026-50258)

  - A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. _XkbSetMapChecks()
    declares a fixed-size stack buffer mapWidths[256] indexed by key type index. The helper function
    CheckKeyTypes() writes to this buffer at a client-controlled offset, allowing a stack buffer overflow.
    This may be used to crash the server, or for privilege escalation if the X server runs as root.
    (CVE-2026-50259)

  - A use-after-free flaw was found in the X.Org X server and Xwayland in FreeCounter(). A client that sets up
    multiple SyncCounters and awaits on those triggers can trigger a use-after-free when destroying those
    counters via a second client connection. This may be used to crash the server, or for privilege escalation
    if the X server runs as root. (CVE-2026-50260)

  - A use-after-free flaw was found in the X.Org X server and Xwayland in SyncChangeCounter(). A client that
    sets up multiple SyncCounters can trigger a use-after-free when destroying those counters via a second
    client connection while changing those counters. This may be used to crash the server, or for privilege
    escalation if the X server runs as root. (CVE-2026-50261)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version
number.");
  # https://security.tuxcare.com/csaf/v2/els_os/centos7els/advisories/2026/clsa-2026_1788424564.json
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?a928bcbd");
  script_set_attribute(attribute:"see_also", value:"https://cve.tuxcare.com/els/releases/CLSA-2026:1788424564");
  script_set_attribute(attribute:"solution", value:
"Update the affected packages based on the guidance in TuxCare advisory CENTOS7:CLSA-2026:1788424564.");
  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:U/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:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-50261");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/06/01");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/09/03");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/09/30");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"CentOS Local Security Checks");

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

  script_dependencies("ssh_get_info2.nasl");
  script_require_keys("Host/OS/extended-third-party", "Host/local_checks_enabled", "Host/CentOS/release", "Host/CentOS/rpm-list");

  exit(0);
}
include('rpm2.inc');

var third_party_support = get_kb_item('Host/OS/extended-third-party');
if (empty_or_null(third_party_support) || third_party_support != 'TuxCare') exit(0, 'TuxCare support not enabled.');

if (!get_kb_item('Host/local_checks_enabled')) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_product = get_kb_item('installed_os/local/SSH/0/product');
if (isnull(os_product) || 'CentOS Linux' >!< os_product) audit(AUDIT_OS_NOT, 'CentOS Linux');
var os_version = get_kb_item('installed_os/local/SSH/0/version');
if (isnull(os_version)) audit(AUDIT_UNKNOWN_APP_VER, 'CentOS Linux');
if (! preg(pattern:"^7([^0-9]|$)", string:os_version)) audit(AUDIT_OS_NOT, 'CentOS Linux 7', 'CentOS Linux ' + os_version);

if (!get_kb_item('Host/CentOS/rpm-list')) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if (cpu !~ "^i[3-6]86$" && 'x86_64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'CentOS Linux', cpu);


var constraints = [
  {
    'release': '7',
    'pkgs': [
      {'reference':'xorg-x11-server-Xdmx-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-Xephyr-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-Xnest-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-Xorg-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-Xvfb-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-Xwayland-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-common-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-devel-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'i686', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-devel-1.20.4-99.el7_9.tuxcare.els11', 'cpu':'x86_64', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'xorg-x11-server-source-1.20.4-99.el7_9.tuxcare.els11', 'el_string':'el7_9', 'rpm_spec_vers_cmp':TRUE}
    ]
  }
];

var os_release = get_one_kb_item('installed_os/local/SSH/0/release');
var os_sp = get_one_kb_item('Host/*/minor_release');

var flag = 0;
var reference;
var sp;
var _cpu;
var el_string;
var rpm_spec_vers_cmp;
var epoch;
var allowmaj;
var exists_check;
var cves;
foreach var constraint ( constraints ) {
  # Check that the target release is equal to the affected release
  if (!empty_or_null(constraint['release'])){
    if (constraint['release'] != os_release) continue;
  }
  if (!empty_or_null(constraint['sp'])){
    if (constraint['sp'] != os_sp) continue;
  }
  foreach var pkg ( constraint['pkgs'] ) {
    reference = NULL;
    sp = NULL;
    _cpu = NULL;
    el_string = NULL;
    rpm_spec_vers_cmp = NULL;
    epoch = NULL;
    allowmaj = NULL;
    exists_check = NULL;
    cves = NULL;
    if (!empty_or_null(pkg['reference'])) reference = pkg['reference'];
    if (!empty_or_null(pkg['sp'])) sp = pkg['sp'];
    if (!empty_or_null(pkg['cpu'])) _cpu = pkg['cpu'];
    if (!empty_or_null(pkg['el_string'])) el_string = pkg['el_string'];
    if (!empty_or_null(pkg['rpm_spec_vers_cmp'])) rpm_spec_vers_cmp = pkg['rpm_spec_vers_cmp'];
    if (!empty_or_null(pkg['epoch'])) epoch = pkg['epoch'];
    if (!empty_or_null(pkg['allowmaj'])) allowmaj = pkg['allowmaj'];
    if (!empty_or_null(pkg['exists_check'])) exists_check = pkg['exists_check'];
    if (!empty_or_null(pkg['cves'])) cves = pkg['cves'];
    if (reference &&
        ## (no known rpm to check OR known rpm_exists)
        (!exists_check || rpm_exists(rpm:exists_check)) &&
        rpm_check(sp:sp, cpu:_cpu, reference:reference, epoch:epoch, el_string:el_string, rpm_spec_vers_cmp:rpm_spec_vers_cmp, allowmaj:allowmaj, cves:cves)) flag++;
  }
}


if (flag)
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : rpm_report_get()
  );
  exit(0);
}
else
{
  var tested = pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'xorg-x11-server-Xdmx / xorg-x11-server-Xephyr / etc');
}