Information Leakage / Sibling Domain Enumeration

Web and APIInfrastructure


Sibling domain enumeration is a type of information leakage vulnerability which occurs when an application uses DNS subdomains to identify user accounts or services, and that information is exposed in a way that enables attackers to enumerate valid user accounts and services. According to the Common Weakness Enumeration (CWE) directory, it is classified as CWE-200, which is an information exposure vulnerability. Additionally, the Open Web Application Security Project (OWASP) Testing Guide identifies this vulnerability as one of the many tests that should be performed during a web application assessment.


Sibling domain enumeration can lead to significant security risks for organizations. Attackers can use this vulnerability to enumerate valid user accounts and services, and then use that information to launch targeted attacks. These attacks can lead to data breaches, system compromise, and other serious security incidents. Organizations should perform regular risk assessments and security testing to identify and mitigate the risk of this vulnerability.


Organizations should take steps to prevent the enumeration of valid user accounts and services. This can be done by limiting access to the DNS zone file, or by using a different authentication mechanism that does not rely on DNS subdomains. Additionally, organizations should perform regular security tests to identify and address any potential vulnerabilities.


The following example demonstrates how attackers can use sibling domain enumeration to enumerate valid user accounts. In this example, an attacker can use the following script to enumerate valid user accounts using DNS subdomains:

#!/usr/bin/env python

import dns.resolver

# domain to enumerate
domain = ""

# list of subdomains to check
subdomains = ["ftp", "mail", "www", "webmail", "dev", "test", "admin"]

# run through subdomains
for sub in subdomains:
    # create DNS query
    query = sub + "." + domain
    print ("[*] Checking " + query)
    # query DNS
        answers = dns.resolver.query(query, 'A')
        for rdata in answers:
            print ("[+] Found " + rdata.address)
        print ("[-] Not found")

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