Actiontec C1000A Modem Backup Account (Telnet)

# SPDX-FileCopyrightText: 2017 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("1.3.6.1.4.1.25623.1.0.112104");
  script_version("2023-07-14T16:09:27+0000");
  script_tag(name:"cvss_base", value:"10.0");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:L/Au:N/C:C/I:C/A:C");
  script_name("Actiontec C1000A Modem Backup Account (Telnet)");
  script_tag(name:"last_modification", value:"2023-07-14 16:09:27 +0000 (Fri, 14 Jul 2023)");
  script_tag(name:"creation_date", value:"2017-11-06 10:23:00 +0200 (Mon, 06 Nov 2017)");
  script_category(ACT_ATTACK);
  script_family("Default Accounts");
  script_copyright("Copyright (C) 2017 Greenbone AG");
  script_dependencies("telnetserver_detect_type_nd_version.nasl", "gb_default_credentials_options.nasl");
  script_require_ports("Services/telnet", 23);
  script_mandatory_keys("telnet/actiontec/modem/detected");
  script_exclude_keys("default_credentials/disable_default_account_checks");

  script_xref(name:"URL", value:"https://www.exploit-db.com/exploits/43118/");

  script_tag(name:"summary", value:"The Actiontec C1000A modem has a backdoor account with hardcoded credentials.");

  script_tag(name:"impact", value:"This issue may be exploited by a remote attacker to gain full
  access to sensitive information or modify system configuration.");

  script_tag(name:"vuldetect", value:"Connect to the telnet service and try to login with default credentials.");

  script_tag(name:"insight", value:"It was possible to login with backup telnet credentials 'admin:CeturyL1nk'.");

  script_tag(name:"solution", value:"It is recommended to disable the telnet access.");

  script_tag(name:"qod_type", value:"exploit");
  script_tag(name:"solution_type", value:"Mitigation");

  exit(0);
}

if(get_kb_item("default_credentials/disable_default_account_checks"))
  exit(0);

include("telnet_func.inc");
include("misc_func.inc");
include("port_service_func.inc");
include("dump.inc");

port = telnet_get_port( default:23 );
banner = telnet_get_banner( port:port );
if( !banner || "===Actiontec xDSL Router===" >!< banner )
  exit( 0 );

login = "admin";
pass  = "CenturyL1nk";

soc = open_sock_tcp( port );
if( ! soc ) exit( 0 );

recv = recv( socket:soc, length:2048 );

if( "Login:" >< recv ) {
  send( socket:soc, data:login + '\r\n' );
  recv = recv( socket:soc, length:128 );

  if( "Password:" >< recv ) {
    send( socket:soc, data:pass + '\r\n\r\n' );
    recv = recv( socket:soc, length:1024 );

    send( socket:soc, data:'sh\r\n' );
    recv = recv( socket:soc, length:1024 );

    if( "BusyBox" >< recv && "built-in shell" >< recv) {
      VULN = TRUE;
      report = 'It was possible to login via telnet using the following backup credentials:\n\n';
      report += 'Login: ' + login + ', Password: ' + pass;
    }
  }
}

close( soc );

if( VULN ) {
  security_message( port:port, data:report );
  exit( 0 );
}

exit( 99 );