Known/Static SSH Host Key Used (TCP)

# SPDX-FileCopyrightText: 2016 Greenbone AG
# Some text descriptions might be excerpted from (a) referenced
# source(s), and are Copyright (C) by the respective right holder(s).
#
# SPDX-License-Identifier: GPL-2.0-only

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.105497");
  script_version("2026-04-14T06:16:47+0000");
  script_name("Known/Static SSH Host Key Used (TCP)");
  # nb: Unlike other VTs we're using the CVEs line by line here for easier addition of new CVEs / to
  #     avoid too large diffs when adding a new CVE.
  script_cve_id("CVE-2008-0166",
                "CVE-2009-4510",
                "CVE-2015-6358",
                "CVE-2015-7255",
                "CVE-2015-7256",
                "CVE-2015-7276",
                "CVE-2015-8251",
                "CVE-2015-8260",
                "CVE-2020-15312",
                "CVE-2020-15313",
                "CVE-2020-15314",
                "CVE-2020-15315",
                "CVE-2020-15316",
                "CVE-2020-15317",
                "CVE-2020-15318",
                "CVE-2020-15319"
               );
  script_tag(name:"cvss_base", value:"8.5");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:M/Au:S/C:C/I:C/A:C");
  script_tag(name:"last_modification", value:"2026-04-14 06:16:47 +0000 (Tue, 14 Apr 2026)");
  script_tag(name:"severity_vector", value:"CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N");
  script_tag(name:"severity_origin", value:"NVD");
  script_tag(name:"severity_date", value:"2018-08-13 21:47:00 +0000 (Mon, 13 Aug 2018)");
  script_tag(name:"creation_date", value:"2016-01-05 13:21:28 +0100 (Tue, 05 Jan 2016)");
  script_category(ACT_GATHER_INFO);
  script_family("SSL and TLS");
  script_copyright("Copyright (C) 2016 Greenbone AG");
  script_dependencies("ssh_proto_version.nasl");
  script_require_ports("Services/ssh", 22);
  script_mandatory_keys("SSH/fingerprints/available");

  script_xref(name:"URL", value:"https://blog.shodan.io/duplicate-ssh-keys-everywhere/");
  script_xref(name:"URL", value:"https://www.kb.cert.org/vuls/id/566724");
  script_xref(name:"URL", value:"https://blogs.intevation.de/thomas/hetzner-duplicate-ed25519-ssh-host-keys/");
  script_xref(name:"URL", value:"https://web.archive.org/web/20180626201156/https://www.vsecurity.com/download/advisories/20100409-2.txt");
  script_xref(name:"URL", value:"https://wiki.debian.org/SSLkeys");
  script_xref(name:"URL", value:"https://www.debian.org/security/2008/dsa-1571");
  script_xref(name:"URL", value:"https://github.com/g0tmi1k/debian-ssh");
  script_xref(name:"URL", value:"https://pierrekim.github.io/blog/2020-03-09-zyxel-secumanager-0day-vulnerabilities.html#ssh-servers-keys");
  script_xref(name:"URL", value:"https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-vulnerabilities-of-cloudcnm-secumanager");
  script_xref(name:"URL", value:"https://sec-consult.com/blog/detail/house-of-keys-industry-wide-https/");
  script_xref(name:"URL", value:"https://sec-consult.com/blog/detail/house-of-keys-9-months-later-40-worse/");
  script_xref(name:"URL", value:"https://github.com/sec-consult/houseofkeys");
  script_xref(name:"URL", value:"https://web.archive.org/web/20180610144949/https://www.sec-consult.com/download/ssh_host_keys.html");
  script_xref(name:"URL", value:"https://web.archive.org/web/20180610144950/https://sec-consult.com/download/certificates.html");

  script_tag(name:"summary", value:"The remote host uses a default SSH host key that is shared among
  multiple installations.");

  script_tag(name:"vuldetect", value:"Checks if the remote host responds with a known SSH host
  key.");

  script_tag(name:"insight", value:"The list of known SSH host keys used by this plugin is
  gathered from various sources:

  - Top 1.000 Duplicate SSH Fingerprints on the Internet collected via the search engine Shodan in
  2015. The most common fingerprint was found to be shared among 245.000 installations where the
  least common was still present 321 times.

  - SSH host keys generated with a vulnerable OpenSSL version on Debian and derivates
  (CVE-2008-0166).

  - Devices of Multiple Vendors (Cisco, ZTE, ZyXEL, OpenStage, OpenScape, TANDBERG) using hardcoded
  SSH host keys (CVE-2015-6358, CVE-2015-7255, CVE-2015-7256, CVE-2015-7276, CVE-2015-8251,
  CVE-2015-8260, CVE-2009-4510).

  - Zyxel CNM SecuManager (CVE-2020-15312, CVE-2020-15313, CVE-2020-15314, CVE-2020-15315,
  CVE-2020-15316, CVE-2020-15317, CVE-2020-15318, CVE-2020-15319)");

  script_tag(name:"impact", value:"An attacker could use this situation to compromise or eavesdrop
  on the SSH communication between the client and the server using a man-in-the-middle attack.");

  script_tag(name:"solution", value:"Generate a new SSH host key.");

  script_tag(name:"solution_type", value:"Workaround");
  script_tag(name:"qod_type", value:"remote_active");

  exit(0);
}

include("bad_ssh_host_keys.inc");
include("ssh_func.inc");
include("misc_func.inc");
include("port_service_func.inc");
include("list_array_func.inc");

# bad_ssh_host_keys.inc might have duplicated host keys for easier
# maintenance so we will make the list here "unique" before
bad_host_keys = make_list_unique( bad_host_keys );

port = ssh_get_port( default:22 );

# nb: "ssh_host_key_algos" is defined as a global var in ssh_func.inc
foreach algo( ssh_host_key_algos ) {

  host_key = get_kb_item( "SSH/" + port + "/fingerprint/" + algo );
  if( ! host_key || ! strlen( host_key ) )
    continue;

  if( in_array( search:host_key, array:bad_host_keys, part_match:FALSE ) ) {
    _report += algo + "  " + host_key + '\n';
    bhk_found = TRUE;
  }

  # Those two are workarounds as we can't include such huge lists into NASL/VTs.
  # The greps will return something like "dd:f3:cc:a5:94:95:d3:75:45:be:26:be:1b:13:e0:05"
  # (including the double apostrophe) if a match was found.
  # nb: Make sure to update the path below if moving the includes or this VT around.
  if( algo == "ssh-rsa" ) {
    argv = make_list( "grep", host_key, "../bad_rsa_ssh_host_keys.txt" );
    res = pread( cmd:"grep", argv:argv, cd:FALSE );
    if( res == '"' + host_key + '"' ) {
      _report += algo + "  " + host_key + '\n';
      bhk_found = TRUE;
    }
  }

  if( algo == "ssh-dss" ) {
    argv = make_list( "grep", host_key, "../bad_dsa_ssh_host_keys.txt" );
    res = pread( cmd:"grep", argv:argv, cd:FALSE );
    if( res == '"' + host_key + '"' ) {
      _report += algo + "  " + host_key + '\n';
      bhk_found = TRUE;
    }
  }
}

if( bhk_found ) {
  report = 'The following known SSH hosts key(s) were found:\n' + _report;
  security_message( port:port, data:report );
  exit( 0 );
}

exit( 99 );