FreeBSD telnetd sys_term.c Environment Variable Handling Privilege Escalation (FreeBSD-SA-09:05)

#
# (C) Tenable Network Security, Inc.
#

include("compat.inc");

if (description)
{
  script_id(35700);
  script_version("1.19");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/06/12");

  script_cve_id("CVE-2009-0641");
  script_bugtraq_id(33777);
  script_xref(name:"EDB-ID", value:"8055");

  script_name(english:"FreeBSD telnetd sys_term.c Environment Variable Handling Privilege Escalation (FreeBSD-SA-09:05)");
  script_summary(english:"Tries to pass LD_DUMP_REL_POST=1 when calling login");

  script_set_attribute(attribute:"synopsis", value:"The remote telnet server is vulnerable to a code execution attack.");
  script_set_attribute(attribute:"description", value:
"A flaw in the environment-handling code used by the telnet server
running on the remote host fails to scrub the environment of variables
such as 'LD_PRELOAD' before calling the login program. An attacker who
can place an arbitrary library on the remote host, either as a local
user or remotely through some other means, can leverage this issue to
execute arbitrary code subject to the privileges under which the
service runs, typically 'root'.");
  script_set_attribute(attribute:"see_also", value:"https://www.freebsd.org/security/advisories/FreeBSD-SA-09:05.telnetd.asc");
  script_set_attribute(attribute:"see_also", value:"https://seclists.org/bugtraq/2009/Feb/150");
  script_set_attribute(attribute:"solution", value:
"Patch or upgrade the affected system as described in the project's
advisory above.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:H/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:F/RL:OF/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");
  script_set_attribute(attribute:"exploit_framework_core", value:"true");
  script_cwe_id(16, 264);

  script_set_attribute(attribute:"plugin_publication_date", value:"2009/02/17");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_end_attributes();

  script_category(ACT_ATTACK);
  script_family(english:"Gain a shell remotely");
  script_copyright(english:"This script is Copyright (C) 2009-2020 Tenable Network Security, Inc.");

  script_dependencies("find_service1.nasl");
  script_require_ports("Services/telnet", 23);

  exit(0);
}


include("global_settings.inc");
include("byte_func.inc");
include("misc_func.inc");
include("telnet2_func.inc");


port = get_kb_item("Services/telnet");
if (!port) port = 23;
if (!get_port_state(port)) exit(0);


global_var rcvdata;


function local_telnet_callback()
{
  local_var data;

  data = _FCT_ANON_ARGS[0];

  # Accumulate each byte as it's received.
  if (data && ord(data[0]) != 0x00 && ord(data[0]) != 0x0d) rcvdata += data[0];

  # There's a problem if we were able to see info about symbol
  # bindings and relocations.
  if (
    'login", relocbase ' >< rcvdata &&
    'libbz2.so", relocbase ' >< rcvdata
  )
  {
    security_hole(port);
    exit(0);
  }
  if ("login: " >< rcvdata || "assword:" >< rcvdata )
  {
    exit(0);
  }
}


# Set up the environment.
env_data =
  mkbyte(0) +
  mkbyte(3) + "LD_DUMP_REL_POST" +
    mkbyte(1) + "1" +
  mkbyte(3) + "LD_PRELOAD" +
    mkbyte(1) + "/usr/lib/libbz2.so" +
  mkbyte(0) + "USER" +
    mkbyte(1) + "nessus";

options = NULL;
options[0] = make_list(OPT_NEW_ENV, env_data);


# Connect and process options.
if (!telnet2_init(port:port, options:options, timeout:5*get_read_timeout()))
  exit(0);

rcvdata = NULL;
telnet_loop(telnet_callback_fn:@local_telnet_callback);