Linux Distros Unpatched Vulnerability : CVE-2026-53994

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

include('compat.inc');

if (description)
{
  script_id(327905);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/07/21");

  script_cve_id("CVE-2026-53994");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-53994");

  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.

  - ProFTPD mod_sftp contains a heap-based buffer overflow reachable by an authenticated SFTP user. The
    fxp_packet_read() function accepts the attacker-supplied 32-bit big-endian SFTP packet length without a
    minimum sanity check. A value of 0 causes an unsigned subtraction elsewhere in the read path to underflow
    to approximately 4 GB. That oversized request reaches the core memory allocator, where the rounded size is
    computed in size_t but passed to new_block() as a 32-bit int; the low 32 bits of 0x100000000 are 0, so
    new_block() returns a small (~512-byte) block while the caller is told it received ~4 GB. The subsequent
    fill loop then streams attacker-controlled bytes past the end of the 544-byte allocation, producing an
    attacker-controlled heap buffer overflow. An authenticated user can crash the per-connection ProFTPD
    session child on demand with a single malformed SFTP packet (packet_len=0 followed by a body greater than
    approximately 544 bytes), producing reliable authenticated remote denial of service. Depending on heap
    layout and adjacent allocations, heap metadata corruption and further consequences beyond denial of
    service may be possible, though only denial of service is demonstrated by the supplied proof of concept.
    (CVE-2026-53994)

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-2026-53994");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2026-53994");
  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:H/Au:S/C:C/I:C/A:C");
  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:L/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:U/RC:C");
  script_set_attribute(attribute:"cvss4_vector", value:"CVSS:4.0/AV:N/AC:H/AT:N/PR:L/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:U");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-53994");

  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:"2026/07/18");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/07/20");

  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:"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:"cpe:/o:debian:debian_linux:11.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:12.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:13.0");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:proftpd-dfsg");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:proftpd-dfsg");
  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-11", "Host/OS/Debian Linux-12", "Host/OS/Debian Linux-13", "Host/OS/Ubuntu Linux-16.04", "Host/OS/Ubuntu Linux-18.04", "Host/OS/Ubuntu Linux-20.04", "Host/OS/Ubuntu Linux-22.04", "Host/OS/Ubuntu Linux-24.04", "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-11": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "11",
        "pkgs": [
          {"reference": "proftpd-basic"},
          {"reference": "proftpd-core"},
          {"reference": "proftpd-dev"},
          {"reference": "proftpd-doc"},
          {"reference": "proftpd-mod-crypto"},
          {"reference": "proftpd-mod-geoip"},
          {"reference": "proftpd-mod-ldap"},
          {"reference": "proftpd-mod-mysql"},
          {"reference": "proftpd-mod-odbc"},
          {"reference": "proftpd-mod-pgsql"},
          {"reference": "proftpd-mod-snmp"},
          {"reference": "proftpd-mod-sqlite"},
          {"reference": "proftpd-mod-wrap"}
        ]
      }
    ]
  },
  "Debian Linux-12": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "12",
        "pkgs": [
          {"reference": "proftpd-basic"},
          {"reference": "proftpd-core"},
          {"reference": "proftpd-dev"},
          {"reference": "proftpd-doc"},
          {"reference": "proftpd-mod-crypto"},
          {"reference": "proftpd-mod-geoip"},
          {"reference": "proftpd-mod-ldap"},
          {"reference": "proftpd-mod-mysql"},
          {"reference": "proftpd-mod-odbc"},
          {"reference": "proftpd-mod-pgsql"},
          {"reference": "proftpd-mod-snmp"},
          {"reference": "proftpd-mod-sqlite"},
          {"reference": "proftpd-mod-wrap"}
        ]
      }
    ]
  },
  "Debian Linux-13": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "13",
        "pkgs": [
          {"reference": "proftpd-core"},
          {"reference": "proftpd-dev"},
          {"reference": "proftpd-doc"},
          {"reference": "proftpd-mod-crypto"},
          {"reference": "proftpd-mod-geoip"},
          {"reference": "proftpd-mod-ldap"},
          {"reference": "proftpd-mod-mysql"},
          {"reference": "proftpd-mod-odbc"},
          {"reference": "proftpd-mod-pgsql"},
          {"reference": "proftpd-mod-snmp"},
          {"reference": "proftpd-mod-sqlite"},
          {"reference": "proftpd-mod-wrap"}
        ]
      }
    ]
  },
  "Ubuntu Linux-16.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "16.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  },
  "Ubuntu Linux-18.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "18.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  },
  "Ubuntu Linux-20.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "20.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  },
  "Ubuntu Linux-22.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "22.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  },
  "Ubuntu Linux-24.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "24.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  },
  "Ubuntu Linux-26.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "26.04",
        "pkgs": [
          {"reference": "proftpd-dfsg"}
        ]
      }
    ]
  }
};

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 third_party_support = get_kb_item('Host/OS/extended-third-party');
if (!empty_or_null(third_party_support)) {
    var third_party_vendors = distro_constraints_values['third_party'];
    if (!empty_or_null(third_party_vendors)) {
        var vendor;
        foreach vendor (third_party_vendors) {
            if (vendor == third_party_support) exit(0, 'A third party management patch is available for this vulnerability from ' + vendor + '.\n');
        }
    }
}

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_HOLE,
      extra      : report
  );
  exit(0);
}
else
{
  audit(AUDIT_HOST_NOT, 'affected');
}