Linux Distros Unpatched Vulnerability : CVE-2026-63091

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

include('compat.inc');

if (description)
{
  script_id(328232);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/07/20");

  script_cve_id("CVE-2026-63091");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-63091");

  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 before 1.3.9c and 1.3.10rc3 contains a signed integer overflow vulnerability in the mod_sftp
    module's SCP size-record parser that allows authenticated low-privilege attackers to bypass ASLR by
    sending a crafted file size value of UINT64_MAX, which results in a negative off_t value. Attackers can
    exploit the subsequent conversion to uint32_t, causing an approximately 4 GB requested read length and
    forcing the server to read beyond the end of the SSH channel data and write overread process memory into
    the uploaded file. In tested configurations, the disclosed data contains libc, libcrypto, and PIE pointers
    sufficient to derive their randomized base addresses, thereby bypassing ASLR and enabling reliable
    exploitation of memory corruption vulnerabilities in the same process. (CVE-2026-63091)

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-2026-63091");
  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:L/PR:L/UI:N/S:U/C:H/I:N/A:N");
  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:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/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-2026-63091");

  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:"2026/07/20");
  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: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: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");

  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"}
        ]
      }
    ]
  }
};

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