Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : Bleach vulnerabilities (USN-8077-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-8077-1. The text
# itself is copyright (C) Canonical, Inc. See
# <https://ubuntu.com/security/notices>. Ubuntu(R) is a registered
# trademark of Canonical, Inc.
##

include('compat.inc');

if (description)
{
  script_id(301534);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/03/09");

  script_cve_id(
    "CVE-2018-7753",
    "CVE-2020-6802",
    "CVE-2020-6816",
    "CVE-2020-6817",
    "CVE-2021-23980"
  );
  script_xref(name:"USN", value:"8077-1");

  script_name(english:"Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : Bleach vulnerabilities (USN-8077-1)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Ubuntu host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The remote Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple
vulnerabilities as referenced in the USN-8077-1 advisory.

    It was discovered that Bleach did not properly sanitize URI attributes containing character entities. An
    attacker could possibly use this issue to construct a URI with a disallowed scheme that would bypass
    sanitization, leading to cross-site scripting. This issue only affected Ubuntu 18.04 LTS. (CVE-2018-7753)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing
    HTML with the noscript tag and a raw tag in the allowed tags list. An attacker could possibly use this
    issue to inject malicious content, leading to cross-site scripting. This issue only affected Ubuntu 18.04
    LTS. (CVE-2020-6802)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing
    HTML with RCDATA together with svg or math tags in the allowed tags list. An attacker could possibly use
    this issue to inject malicious content, leading to cross-site scripting. (CVE-2020-6816)

    It was discovered that Bleach incorrectly handled parsing of style attributes when sanitizing HTML. An
    attacker could possibly use this issue to perform a regular expression denial of service, leading to
    excessive resource consumption. (CVE-2020-6817)

    Yaniv Nizry and Micha Bentkowski discovered that Bleach was vulnerable to a mutation cross-site
    scripting issue when sanitizing HTML with certain combinations of allowed tags. An attacker could possibly
    use this issue to inject malicious content, leading to cross-site scripting. (CVE-2021-23980)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version
number.");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/notices/USN-8077-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected python-bleach and / or python3-bleach packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:P/RL:O/RC:C");
  script_set_attribute(attribute:"cvss4_vector", value:"CVSS:4.0/AV:N/AC:L/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-2018-7753");

  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:"2018/03/06");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/03/05");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/03/09");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:16.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:18.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:20.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:python-bleach");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:python3-bleach");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

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

  script_copyright(english:"Ubuntu Security Notice (C) 2026 Canonical, Inc. / NASL script (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info.nasl", "ubuntu_pro_sub_detect.nasl");
  script_require_keys("Host/cpu", "Host/Ubuntu", "Host/Ubuntu/release", "Host/Debian/dpkg-l");

  exit(0);
}

include('debian_package.inc');

if ( ! get_kb_item('Host/local_checks_enabled') ) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_release = get_kb_item('Host/Ubuntu/release');
if ( isnull(os_release) ) audit(AUDIT_OS_NOT, 'Ubuntu');
os_release = chomp(os_release);
if (! ('16.04' >< os_release || '18.04' >< os_release || '20.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 16.04 / 18.04 / 20.04', 'Ubuntu ' + os_release);
if ( ! get_kb_item('Host/Debian/dpkg-l') ) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ('x86_64' >!< cpu && cpu !~ "^i[3-6]86$" && 's390' >!< cpu && 'aarch64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'Ubuntu', cpu);
var ubuntu_pro_detected = get_kb_item('Host/Ubuntu/Pro/Services/esm-apps');
ubuntu_pro_detected = !empty_or_null(ubuntu_pro_detected);

var pro_caveat_needed = FALSE;

var pkgs = [
    {'osver': '16.04', 'pkgname': 'python-bleach', 'pkgver': '1.4.2-1ubuntu0.1~esm1', 'ubuntu_pro': TRUE, 'cves': ['CVE-2020-6816', 'CVE-2020-6817', 'CVE-2021-23980']},
    {'osver': '16.04', 'pkgname': 'python3-bleach', 'pkgver': '1.4.2-1ubuntu0.1~esm1', 'ubuntu_pro': TRUE, 'cves': ['CVE-2020-6816', 'CVE-2020-6817', 'CVE-2021-23980']},
    {'osver': '18.04', 'pkgname': 'python-bleach', 'pkgver': '2.1.2-1ubuntu0.1~esm1', 'ubuntu_pro': TRUE, 'cves': ['CVE-2018-7753', 'CVE-2020-6802', 'CVE-2020-6816', 'CVE-2020-6817', 'CVE-2021-23980']},
    {'osver': '18.04', 'pkgname': 'python3-bleach', 'pkgver': '2.1.2-1ubuntu0.1~esm1', 'ubuntu_pro': TRUE, 'cves': ['CVE-2018-7753', 'CVE-2020-6802', 'CVE-2020-6816', 'CVE-2020-6817', 'CVE-2021-23980']},
    {'osver': '20.04', 'pkgname': 'python3-bleach', 'pkgver': '3.1.1-1ubuntu0.1~esm1', 'ubuntu_pro': TRUE, 'cves': ['CVE-2020-6816', 'CVE-2020-6817', 'CVE-2021-23980']}
];

var flag = 0;
foreach var package_array ( pkgs ) {
  var osver = NULL;
  var pkgname = NULL;
  var pkgver = NULL;
  if (!empty_or_null(package_array['osver'])) osver = package_array['osver'];
  if (!empty_or_null(package_array['pkgname'])) pkgname = package_array['pkgname'];
  if (!empty_or_null(package_array['pkgver'])) pkgver = package_array['pkgver'];
  if (!empty_or_null(package_array['cves'])) cves = package_array['cves'];
  var pro_required = NULL;
  if (!empty_or_null(package_array['ubuntu_pro'])) pro_required = package_array['ubuntu_pro'];
  if (osver && pkgname && pkgver) {
    if (deb_check(release:osver, prefix:pkgname, reference:pkgver, cves:cves)) {
        flag++;
        if (!ubuntu_pro_detected && !pro_caveat_needed) pro_caveat_needed = pro_required;
    }
  }
}

if (flag)
{
  var extra = '';
  if (pro_caveat_needed) {
    extra += 'NOTE: This vulnerability check contains fixes that apply to packages only \n';
    extra += 'available in Ubuntu ESM repositories. Access to these package security updates \n';
    extra += 'require an Ubuntu Pro subscription.\n\n';
  }
  extra += ubuntu_report_get();
  security_report_v4(
    port       : 0,
    severity   : SECURITY_HOLE,
    extra      : extra
  );
  exit(0);
}
else
{
  var tested = ubuntu_pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'python-bleach / python3-bleach');
}