IMAP arbitrary file retrieval

# SPDX-FileCopyrightText: 2004 George A. Theall
# 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("1.3.6.1.4.1.25623.1.0.12254");
  script_version("2023-08-01T13:29:10+0000");
  script_tag(name:"last_modification", value:"2023-08-01 13:29:10 +0000 (Tue, 01 Aug 2023)");
  script_tag(name:"creation_date", value:"2005-11-03 14:08:04 +0100 (Thu, 03 Nov 2005)");
  script_tag(name:"cvss_base", value:"2.1");
  script_tag(name:"cvss_base_vector", value:"AV:L/AC:L/Au:N/C:P/I:N/A:N");
  script_cve_id("CVE-2002-1782");
  script_name("IMAP arbitrary file retrieval");
  script_category(ACT_ATTACK);
  script_copyright("Copyright (C) 2004 George A. Theall");
  script_family("Remote file access");
  script_dependencies("imap4_banner.nasl", "logins.nasl");
  script_require_ports("Services/imap", 143);
  script_mandatory_keys("imap/banner/available", "imap/login", "imap/password");

  script_xref(name:"URL", value:"http://www.washington.edu/imap/IMAP-FAQs/index.html#5.1");
  script_xref(name:"URL", value:"http://www.securityfocus.com/bid/4909");

  script_tag(name:"solution", value:"Contact your vendor for a fix.");

  script_tag(name:"summary", value:"The target is running an IMAP daemon that allows an authenticated user
  to retrieve and manipulate files that would be available to that user via a shell. If IMAP users are denied
  shell access, you may consider this a vulnerability.");

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

  exit(0);
}

include("misc_func.inc");
include("port_service_func.inc");
include("imap_func.inc");

kb_creds = imap_get_kb_creds();
user = kb_creds["login"];
pass = kb_creds["pass"];
if (!user || !pass)
  exit(0);

file = "/etc/group"; # file to grab from target.

port = imap_get_port(default:143);

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

s = recv_line(socket:soc, length:1024);
if (!strlen(s)) {
  close(soc);
  exit(0);
}
s = chomp(s);

#
# - try the PLAIN SASL mechanism.
#   nb: RFC 3501 requires this be supported by imap4rev1 servers, although
#       it may also require SSL / TLS encapsulation.
++tag;
c = string("a", string(tag), ' AUTHENTICATE "PLAIN"');
send(socket:soc, data:string(c, "\r\n"));
s = recv_line(socket:soc, length:1024);
s = chomp(s);
if (s =~ "^\+") {
  c = base64(str:raw_string(0, user, 0, pass));
  send(socket:soc, data:string(c, "\r\n"));
  # nb: I'm not sure why, but the following recv_line often times out
  #     unless I either sleep for a bit before or specify a timeout
  #     even though the actual delay / timeout seems irrelevant.
  while (s = recv_line(socket:soc, length:1024, timeout:1)) {
    s = chomp(s);
    m = eregmatch(pattern:string("^a", string(tag), " (OK|BAD|NO)"), string:s, icase:TRUE);
    if (!isnull(m)) {
      resp = m[1];
      break;
    }
    resp = "";
  }
}

# If that didn't work, try LOGIN command.
if (isnull(resp)) {
  ++tag;
  c = string("a", string(tag), " LOGIN ", user, " ", pass);
  send(socket:soc, data:string(c, "\r\n"));
  while (s = recv_line(socket:soc, length:1024)) {
    s = chomp(s);
    m = eregmatch(pattern:string("^a", string(tag), " (OK|BAD|NO)"), string:s, icase:TRUE);
    if (!isnull(m)) {
      resp = m[1];
      break;
    }
    resp = "";
  }
}

# If successful, try to select an arbitrary file to use as a mailbox.
if (resp && resp =~ "OK") {
  ++tag;
  c = string("a", string(tag), ' SELECT "', file, '"');
  send(socket:soc, data:string(c, "\r\n"));
  while (s = recv_line(socket:soc, length:1024)) {
    s = chomp(s);
    m = eregmatch(pattern:string("^a", string(tag), " (OK|BAD|NO)"), string:s, icase:TRUE);
    if (!isnull(m)) {
      resp = m[1];
      break;
    }
    resp = "";
  }

  # If successful, try to read the file.
  #
  # NB: this isn't really necessary since the previous command,
  #     if successful, means we can read the file.
  if (resp && resp =~ "OK") {
    ++tag;
    c = string("a", string(tag), " FETCH 1 rfc822");
    send(socket:soc, data:string(c, "\r\n"));
    while (s = recv_line(socket:soc, length:1024)) {
      s = chomp(s);
      m = eregmatch(pattern:string("^a", string(tag), " (OK|BAD|NO)"), string:s, icase:TRUE);
      if (!isnull(m)) {
        resp = m[1];
        break;
      }
      resp = "";
    }
    if (resp && resp =~ "OK") security_message(port);
  }
}

# Logout.
++tag;
c = string("a", string(tag), " LOGOUT");
send(socket:soc, data:string(c, "\r\n"));
while (s = recv_line(socket:soc, length:1024)) {
  s = chomp(s);
  m = eregmatch(pattern:string("^a", string(tag), " (OK|BAD|NO)"), string:s, icase:TRUE);
  if (!isnull(m)) {
    resp = m[1];
    break;
  }
  resp = "";
}
close(soc);