Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS : libssh vulnerabilities (USN-8699-1)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-8699-1. 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(365394);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/10/13");

  script_cve_id(
    "CVE-2026-15370",
    "CVE-2026-59843",
    "CVE-2026-59844",
    "CVE-2026-59845",
    "CVE-2026-59846",
    "CVE-2026-59847",
    "CVE-2026-59848",
    "CVE-2026-59849",
    "CVE-2026-59850"
  );
  script_xref(name:"USN", value:"8699-1");

  script_name(english:"Ubuntu 22.04 LTS / 24.04 LTS / 26.04 LTS : libssh vulnerabilities (USN-8699-1)");

  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 22.04 LTS / 24.04 LTS / 26.04 LTS host has packages installed that are affected by multiple
vulnerabilities as referenced in the USN-8699-1 advisory.

    It was discovered that libssh had a stack buffer overflow in its SFTP server when constructing directory
    listing entries for long filenames. An attacker could possibly use this issue to cause libssh to crash or
    execute arbitrary code. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-15370)

    It was discovered that libssh did not correctly handle SSH channel open messages advertising a zero
    maximum packet size. An authenticated remote attacker could possibly use this issue to cause libssh to
    consume excessive CPU resources, leading to a denial of service. (CVE-2026-59843)

    It was discovered that libssh did not correctly limit SFTP read request lengths in its server
    implementation. An authenticated remote attacker could possibly use this issue to cause libssh to allocate
    excessive memory, leading to a denial of service. This issue only affected Ubuntu 26.04 LTS.
    (CVE-2026-59844)

    It was discovered that libssh did not correctly handle ProxyCommand fork() failures. A local attacker
    could possibly use this issue to cause a denial of service. (CVE-2026-59845)

    It was discovered that libssh did not correctly sanitize shell metacharacters when expanding usernames in
    ProxyCommand strings. An attacker could possibly use this issue to obtain sensitive information.
    (CVE-2026-59846)

    It was discovered that libssh had incorrect AES-GCM tag verification when built with the OpenSSL backend.
    A machine-in-the-middle attacker could possibly use this issue to modify encrypted traffic without
    detection. (CVE-2026-59847)

    It was discovered that libssh did not correctly handle SFTP server responses for unknown request IDs. An
    attacker could possibly use this issue to cause libssh to use excessive memory, leading to a denial of
    service. (CVE-2026-59848)

    It was discovered that libssh had logic errors in certificate-based authentication that could cause
    clients to loop indefinitely when certificates were rejected. An attacker could possibly use this issue to
    cause a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-59849)

    It was discovered that libssh could invoke data callbacks on channels after they had been closed. An
    attacker could possibly use this issue to cause libssh to crash or execute arbitrary code.
    (CVE-2026-59850)

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-8699-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected libssh-4 and / or libssh-gcrypt-4 packages.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:C/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:N/UI:N/S:U/C:N/I:H/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-2026-59847");

  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:"2026/07/21");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/08/31");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/10/13");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:22.04:-: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:libssh-4");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:libssh-gcrypt-4");
  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_info2.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 (! ('22.04' >< os_release || '24.04' >< os_release || '26.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 22.04 / 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': '22.04', 'pkgname': 'libssh-4', 'pkgver': '0.9.6-2ubuntu0.22.04.8', 'cves': ['CVE-2026-59843', 'CVE-2026-59845', 'CVE-2026-59846', 'CVE-2026-59847', 'CVE-2026-59848', 'CVE-2026-59850']},
    {'osver': '22.04', 'pkgname': 'libssh-gcrypt-4', 'pkgver': '0.9.6-2ubuntu0.22.04.8', 'cves': ['CVE-2026-59843', 'CVE-2026-59845', 'CVE-2026-59846', 'CVE-2026-59847', 'CVE-2026-59848', 'CVE-2026-59850']},
    {'osver': '24.04', 'pkgname': 'libssh-4', 'pkgver': '0.10.6-2ubuntu0.5', 'cves': ['CVE-2026-59843', 'CVE-2026-59845', 'CVE-2026-59846', 'CVE-2026-59847', 'CVE-2026-59848', 'CVE-2026-59850']},
    {'osver': '24.04', 'pkgname': 'libssh-gcrypt-4', 'pkgver': '0.10.6-2ubuntu0.5', 'cves': ['CVE-2026-59843', 'CVE-2026-59845', 'CVE-2026-59846', 'CVE-2026-59847', 'CVE-2026-59848', 'CVE-2026-59850']},
    {'osver': '26.04', 'pkgname': 'libssh-4', 'pkgver': '0.11.3-1ubuntu2.1', 'cves': ['CVE-2026-15370', 'CVE-2026-59843', 'CVE-2026-59844', 'CVE-2026-59845', 'CVE-2026-59846', 'CVE-2026-59847', 'CVE-2026-59848', 'CVE-2026-59849', 'CVE-2026-59850']}
];

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