UhOh365 : A Script That Can See If An Email Address Is Valid In Office365

UhOh365 is a script that can see if an email address is valid in Office365. This does not perform any login attempts, is unthrottled, and is incredibly useful for social engineering assessments to find which emails exist and which don’t.

Microsoft does not consider “email enumeration” a vulnerability, so this is taking advantage of a “feature”. There are a couple other public Office365 email validation scripts out there, but they all (that I have seen) require at least 1 login attempt per user account. That is detectable and can be found as a light bruteforce attempt (1 “common” password across multiple accounts).

This script allows for email validation with zero login attempts and only uses Microsoft’s built-in Autodiscover API so it is invisible to the person/company who owns the email address. Furthermore, this API call appears to be completely unthrottled and I was able to validate over 2,000 email addresses within 1 minute in my testing.

Usage

The script is actually really basic and easy to use. You make a file of the emails you want to see are valid or not and pass it as an argument to the script. Or you can provide a file just of usernames and give the -s argument to automatically append a suffix to each entry:

Usage: UhOh365.py [-h] [-v] [-t THREADS] [-o OUTPUT] file

Positional Arguments:
file Input file containing one email per line

Optional Arguments:
-h, –help show this help message and exit
-v, –verbose Display each result as valid/invalid. By default only displays valid
-s, –suffix Add a domain suffix to every input line from file (e.g: contoso.com)
-t THREADS, –threads THREADS
Number of threads to run with. Default is 20
-o OUTPUT, –output OUTPUT
Output file for valid emails only
-n, –nossl Turn off SSL verification. This can increase speed if
needed
-p PROXY, –proxy PROXY
Specify a proxy to run this through (eg: ‘http://127.0.0.1:8080’)

Explanation

This is actually a very easy thing to do. It turns out the /autodiscover/autodiscover.json/v1.0/{EMAIL}?Protocol=Autodiscoverv1 API endpoint returns different status codes for if an email exists in o365 or not. 200 status code means it exists, a 302 means it doesn’t exist.

  • If the email does exist:
  • If the email does not exist:

Notice this request takes zero authentication or identifying parameters and it does not cause a login attempt on the target account.

Credit: Chris King

R K

Recent Posts

ROADTools: The Modern Azure AD Exploration Framework

ROADTools is a powerful framework designed for exploring and interacting with Microsoft Azure Active Directory…

14 hours ago

How to Enumerate Microsoft 365 Groups Using PowerShell and Python

Microsoft 365 Groups (also known as M365 Groups or Unified Groups) are at the heart…

15 hours ago

SeamlessPass: Using Kerberos Tickets to Access Microsoft 365

SeamlessPass is a specialized tool designed to leverage on-premises Active Directory Kerberos tickets to obtain…

2 days ago

PPLBlade: Advanced Memory Dumping and Obfuscation Tool

PPLBlade is a powerful Protected Process Dumper designed to capture memory from target processes, hide…

2 days ago

HikPwn : Simple Scanner For Hikvision Devices With Basic Vulnerability Scanning

HikPwn: Comprehensive Guide to Scanning Hikvision Devices for Vulnerabilities If you’re searching for an efficient…

2 days ago

Comments in Bash Scripts

What Are Bash Comments? Comments in Bash scripts, are notes in your code that the…

1 week ago