Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : libssh vulnerabilities (USN-7696-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-7696-1. 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(252946);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2025/08/20");

  script_cve_id("CVE-2025-4877", "CVE-2025-4878", "CVE-2025-5318");
  script_xref(name:"USN", value:"7696-1");

  script_name(english:"Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : libssh vulnerabilities (USN-7696-1)");

  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-7696-1 advisory.

    Ronald Crane discovered that libssh incorrectly handled certain base64 conversions. An attacker could use
    this issue to cause libssh to crash, resulting in a denial of service, or possibly execute arbitrary code.
    (CVE-2025-4877)

    Ronald Crane discovered that libssh incorrectly handled the privatekey_from_file() function. An attacker
    could use this issue to cause libssh to crash, resulting in a denial of service, or possibly execute
    arbitrary code. (CVE-2025-4878)

    Ronald Crane discovered that libssh incorrectly handled certain memory operations in the sftp server. An
    attacker could possibly use this issue to cause libssh to crash, resulting in a denial of service.
    (CVE-2025-5318)

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-7696-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:S/C:P/I:P/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2025-5318");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2025/06/24");
  script_set_attribute(attribute:"patch_publication_date", value:"2025/08/14");
  script_set_attribute(attribute:"plugin_publication_date", value:"2025/08/20");

  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:libssh-4");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libssh-dev");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libssh-gcrypt-4");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libssh-gcrypt-dev");
  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) 2025 Canonical, Inc. / NASL script (C) 2025 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': 'libssh-4', 'pkgver': '0.6.3-4.3ubuntu0.6+esm2', 'ubuntu_pro': TRUE},
    {'osver': '16.04', 'pkgname': 'libssh-dev', 'pkgver': '0.6.3-4.3ubuntu0.6+esm2', 'ubuntu_pro': TRUE},
    {'osver': '16.04', 'pkgname': 'libssh-gcrypt-4', 'pkgver': '0.6.3-4.3ubuntu0.6+esm2', 'ubuntu_pro': TRUE},
    {'osver': '16.04', 'pkgname': 'libssh-gcrypt-dev', 'pkgver': '0.6.3-4.3ubuntu0.6+esm2', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'libssh-4', 'pkgver': '0.8.0~20170825.94fa1e38-1ubuntu0.7+esm4', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'libssh-dev', 'pkgver': '0.8.0~20170825.94fa1e38-1ubuntu0.7+esm4', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'libssh-gcrypt-4', 'pkgver': '0.8.0~20170825.94fa1e38-1ubuntu0.7+esm4', 'ubuntu_pro': TRUE},
    {'osver': '18.04', 'pkgname': 'libssh-gcrypt-dev', 'pkgver': '0.8.0~20170825.94fa1e38-1ubuntu0.7+esm4', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'libssh-4', 'pkgver': '0.9.3-2ubuntu2.5+esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'libssh-dev', 'pkgver': '0.9.3-2ubuntu2.5+esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'libssh-gcrypt-4', 'pkgver': '0.9.3-2ubuntu2.5+esm1', 'ubuntu_pro': TRUE},
    {'osver': '20.04', 'pkgname': 'libssh-gcrypt-dev', 'pkgver': '0.9.3-2ubuntu2.5+esm1', 'ubuntu_pro': TRUE}
];

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_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, 'libssh-4 / libssh-dev / libssh-gcrypt-4 / libssh-gcrypt-dev');
}