Ubuntu 14.04 LTS / 18.04 LTS / 20.04 LTS / 24.04 LTS / 26.04 LTS : libass vulnerabilities (USN-8815-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-8815-1. 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(350176);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/09/25");

  script_cve_id(
    "CVE-2020-24994",
    "CVE-2020-26682",
    "CVE-2026-61626",
    "CVE-2026-61627"
  );
  script_xref(name:"USN", value:"8815-1");

  script_name(english:"Ubuntu 14.04 LTS / 18.04 LTS / 20.04 LTS / 24.04 LTS / 26.04 LTS : libass vulnerabilities (USN-8815-1)");

  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 14.04 LTS / 18.04 LTS / 20.04 LTS / 24.04 LTS / 26.04 LTS host has packages installed that are
affected by multiple vulnerabilities as referenced in the USN-8815-1 advisory.

    It was discovered that libass incorrectly handled parsing operations for specific nested character
    strings. An attacker could use this issue to cause libass to crash, resulting in a denial of service, or
    possibly execute arbitrary code. This issue only affected Ubuntu 14.04 LTS, Ubuntu 16.04 LTS, Ubuntu 18.04
    LTS and Ubuntu 20.04 LTS. (CVE-2020-24994)

    It was discovered that libass incorrectly handled certain outline processing operations. An attacker could
    use this issue to cause libass to crash, resulting in a denial of service. This issue only affected Ubuntu
    18.04 LTS and Ubuntu 20.04 LTS. (CVE-2020-26682)

    It was discovered that libass incorrectly handled certain ASS subtitle files when measuring wrapped lines.
    An attacker could use this issue to cause libass to crash, resulting in a denial of service, or possibly
    execute arbitrary code. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-61627)

    It was discovered that libass incorrectly handled certain Matroska subtitle chunks with negative ReadOrder
    values. An attacker could use this issue to cause libass to crash, resulting in a denial of service, or
    possibly execute arbitrary code. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-61626)

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-8815-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected libass4 and / or libass9 packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/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:R/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:"cvss_score_source", value:"CVE-2020-26682");

  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:"2020/10/16");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/09/24");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/09/25");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:14.04:-: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:"cpe:/o:canonical:ubuntu_linux:24.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:26.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libass4");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libass9");
  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");
  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 (! ('14.04' >< os_release || '18.04' >< os_release || '20.04' >< os_release || '24.04' >< os_release || '26.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 14.04 / 18.04 / 20.04 / 24.04 / 26.04', '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 pkgs = [
    {'osver': '14.04', 'pkgname': 'libass4', 'pkgver': '0.10.1-3ubuntu1+esm2', 'cves': ['CVE-2020-24994']},
    {'osver': '18.04', 'pkgname': 'libass9', 'pkgver': '1:0.14.0-1ubuntu0.1~esm1', 'cves': ['CVE-2020-24994', 'CVE-2020-26682']},
    {'osver': '20.04', 'pkgname': 'libass9', 'pkgver': '1:0.14.0-2ubuntu0.1~esm1', 'cves': ['CVE-2020-24994', 'CVE-2020-26682']},
    {'osver': '24.04', 'pkgname': 'libass9', 'pkgver': '1:0.17.1-2ubuntu0.1~esm1', 'cves': ['CVE-2026-61627']},
    {'osver': '26.04', 'pkgname': 'libass9', 'pkgver': '1:0.17.4-2ubuntu0.1~esm1', 'cves': ['CVE-2026-61626', 'CVE-2026-61627']}
];

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'];
  if (osver && pkgname && pkgver) {
    if (deb_check(release:osver, prefix:pkgname, reference:pkgver, cves:cves)) flag++;
  }
}

if (flag)
{
  var extra = '';
  extra += ubuntu_report_get();
  security_report_v4(
    port       : 0,
    severity   : SECURITY_WARNING,
    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, 'libass4 / libass9');
}