Linux Distros Unpatched Vulnerability : CVE-2026-42768

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

include('compat.inc');

if (description)
{
  script_id(320343);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/06/10");

  script_cve_id("CVE-2026-42768");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-42768");

  script_set_attribute(attribute:"synopsis", value:
"The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be
patched.");
  script_set_attribute(attribute:"description", value:
"The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied
patch available.

  - Issue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to Bleichenbacher-style attack
    when an attacker is able to provide the CMS or S/MIME messages and observe the error code and/or
    decryption output. Impact summary: The Bleichenbacher-style attack allows an attacker to use the victim's
    vulnerable application as a way to decrypt or sign messages with the victim's private RSA key. The attack
    is possible in 2 variants. 1. The decryption API (CMS_decrypt(), PKCS7_decrypt()) is used without
    providing the recipient certificate. In this case OpenSSL iterates over every KeyTransRecipientInfo (KTRI)
    without stopping at the first success. An attacker who authors a message with two KTRI entries  the first
    one wrapping a real CEK under the victim's public key, the second with an arbitrary probe ciphertext 
    obtains opportunity to iterate the 2nd KTRI to get a valid PKCS#1 v1.5 padding if the error code of the
    application is available. That is a Bleichenbacher oracle (Bleichenbacher, CRYPTO '98): an adaptive-
    chosen-ciphertext side channel from which the attacker decrypts any RSA ciphertext to the victim's key or
    forges any PKCS#1 v1.5 signature under it. 2. When the decryption API (CMS_decrypt(), PKCS7_decrypt()) is
    provided with the recipient certificate, and the recipient is not found, a random key is substituted. An
    attacker who authors a message and is able to compare both error code and the result of the decryption,
    can mount a Bleichenbacher oracle. We are not aware of any applications that provide a remote attacker an
    opportunity to mount an attack described in these scenarios. We consider the existence of such application
    very unlikely, and for this reason this CVE has been evaluated as Low severity. To avoid these attacks,
    when RSA PKCS#1 v1.5 Key Transport is in use, the invoked EVP_PKEY_decrypt() will use the implicit
    rejection mechanism described in draft-irtf-cfrg-rsa-guidance. In previous OpenSSL releases the implicit
    rejection was explicitly disabled. The implicit rejection mechanism always returns a plaintext value, the
    symmetric key. This result is deterministic for the ciphertext and the private key. The length of the
    decryption result can happen to match the length of the key of the symmetric cipher that was used for the
    content encryption. When a certificate is not provided, the last RecipientInfo producing a key that looks
    valid will be used. It may cause getting garbage content on decryption. As a proper way to deal with this
    a recipient certificate has to be provided to identify the particular RecipientInfo for decryption. The
    FIPS modules in 4.0, 3.6, 3.5, and 3.4 are not affected by this issue, as CMS and S/MIME processing
    happens outside the OpenSSL FIPS module boundary. (CVE-2026-42768)

Note that Nessus relies on the presence of the package as reported by the vendor.");
  script_set_attribute(attribute:"see_also", value:"https://security-tracker.debian.org/tracker/CVE-2026-42768");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2026-42768");
  script_set_attribute(attribute:"solution", value:
"There is no known solution at this time.");
  script_set_attribute(attribute:"agent", value:"unix");
  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:U/RL:U/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:U/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-42768");

  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_unpatched", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/06/09");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/06/10");

  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:25.10");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:26.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:14.0");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:edk2");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:nodejs");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:openssl");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:openssl");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Misc.");

  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", "set_linux_os_id.nasl");
  script_require_keys("Host/cpu", "Host/local_checks_enabled", "global_settings/vendor_unpatched", "Host/OS/identifier");
  script_require_ports("Host/OS/Debian Linux-14", "Host/OS/Ubuntu Linux-22.04", "Host/OS/Ubuntu Linux-25.10", "Host/OS/Ubuntu Linux-26.04");

  exit(0);
}

if (!get_kb_item("global_settings/vendor_unpatched")) exit(0, "Unpatched Vulnerabilities Detection not active.");
if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (empty_or_null(get_one_kb_item("Host/Debian/dpkg-l"))) audit(AUDIT_PACKAGE_LIST_MISSING);

include('linux_unpatched.inc');

var distro_constraints_array = {
  "Debian Linux-14": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14",
        "pkgs": [
          {"reference": "libcrypto3-udeb"},
          {"reference": "libssl-dev"},
          {"reference": "libssl-doc"},
          {"reference": "libssl3-udeb"},
          {"reference": "libssl3t64"},
          {"reference": "openssl"},
          {"reference": "openssl-provider-fips"},
          {"reference": "openssl-provider-legacy"}
        ]
      }
    ]
  },
  "Ubuntu Linux-22.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "22.04",
        "pkgs": [
          {"reference": "nodejs"}
        ]
      }
    ]
  },
  "Ubuntu Linux-25.10": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "25.10",
        "pkgs": [
          {"reference": "efi-shell-aa64"},
          {"reference": "efi-shell-arm"},
          {"reference": "efi-shell-ia32"},
          {"reference": "efi-shell-loongarch64"},
          {"reference": "efi-shell-riscv64"},
          {"reference": "efi-shell-x64"},
          {"reference": "libcrypto3-udeb"},
          {"reference": "libssl-dev"},
          {"reference": "libssl-doc"},
          {"reference": "libssl3-udeb"},
          {"reference": "libssl3t64"},
          {"reference": "openssl"},
          {"reference": "openssl-provider-legacy"},
          {"reference": "ovmf"},
          {"reference": "ovmf-ia32"},
          {"reference": "ovmf-inteltdx"},
          {"reference": "qemu-efi-aarch64"},
          {"reference": "qemu-efi-arm"},
          {"reference": "qemu-efi-loongarch64"},
          {"reference": "qemu-efi-riscv64"}
        ]
      }
    ]
  },
  "Ubuntu Linux-26.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "26.04",
        "pkgs": [
          {"reference": "efi-shell-aa64"},
          {"reference": "efi-shell-loongarch64"},
          {"reference": "efi-shell-riscv64"},
          {"reference": "efi-shell-x64"},
          {"reference": "libcrypto3-udeb"},
          {"reference": "libssl-dev"},
          {"reference": "libssl-doc"},
          {"reference": "libssl3-udeb"},
          {"reference": "libssl3t64"},
          {"reference": "openssl"},
          {"reference": "openssl-provider-legacy"},
          {"reference": "ovmf"},
          {"reference": "ovmf-amdsev"},
          {"reference": "ovmf-generic"},
          {"reference": "ovmf-inteltdx"},
          {"reference": "ovmf-legacy"},
          {"reference": "qemu-efi-aarch64"},
          {"reference": "qemu-efi-loongarch64"},
          {"reference": "qemu-efi-riscv64"}
        ]
      }
    ]
  }
};

var distro_constraints_values = linux_unpatched::get_distro_constraints(distro_constraints_arr:distro_constraints_array);
if (empty_or_null(distro_constraints_values)) audit(AUDIT_HOST_NOT, 'affected');
var report = linux_unpatched::check_unpatched_constraints(distro_constraints_values:distro_constraints_values);

if (!empty_or_null(report))
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : report
  );
  exit(0);
}
else
{
  audit(AUDIT_HOST_NOT, 'affected');
}