This document discusses security issues with SSL certificate validation processes that rely on email verification. Specifically, it describes how many certificate authorities would accept registration emails to common addresses like admin@domain.com, allowing attackers to potentially obtain fraudulent certificates. The document outlines the fixes made to certification policies to address this, but notes there are still avenues of abuse if certain email providers do not properly validate ownership of addresses.

1. The life and times of
Hanz Ostmaster
By Hanz Ostmaster

2. Chaim Sanders
 Trustwave
 Security Researcher
 Member of Spiderlabs Research
 Web Server Security Team
 Offer support, development, and consulting for ModSecurity
 Supports the OWASP Core Rule Set
 Work with Trustwave WAF
 Rochester Institute of Technology
 Professor (Cryptography and Web Security)
 Prior
 Security Consulting (Pentesting, Red-teaming, Code Review, etc)
 Governmental Consulting
Background

3. Crypto and you
 Generally speaking the area of research regarding secret
writing and methods for attacking these secret writings
has been of interest
 Cryptography – Development of enciphered writings
 Cryptanalysis – Attacking of enciphered writing schemes
 Why do I care?
 Since the mid 80’s we’ve seen cryptographic systems evolve from
tools of military interest to common usage within our daily lives.
 To counter this many (governmental) organizations that have come
to rely on their ability to in some way compromise crypto.

4. Asymmetric Crypto
 There are many different areas of Cryptography

5. Asymmetric Crypto and this talk
 One of the biggest uses of asymmetric crypto into todays
infrastructure is for securing communication between
webservers
 Why might this be of interest?
 How do we ensure speed?
 Asymmetric crypto has two very nice features
 One is scale, as we previously discussed
 The other is that they often have support for digital signatures
 What is a digital signature.

6. What is SSL
 SSL stands for Secure Sockets Layer and it is a standard security
technology for establishing an encrypted link between a server and a
client
 First SSL Certificate was created in 1994 by Netscape Communications
 SSL Certificate issuers are called Certificate Authority or CA’s
 SSL allows sensitive information such as credit card numbers and
social security numbers to be transmitted securely
 Required by the Payment Card Industry (PCI) to have an SSL
Certificate
 Main component of SSL Certificates are keys which are the Public and
Private key

7. Design Requirements of Asymmetric
System
 The main design requirement is that all parties trust this
Certificate Authority
 Additionally, the certificate authority must only issue
certificates to legitimate hosts
 The question becomes how does a CA like Symantec verify that
individuals are responsible for legitimatize hosts.
 This is the interest of todays talk.

8. Host verification
 There are a number of different methods that ICANN has
specified for allowing CA’s to verify users:
 HTTP Validation – Can be performed by uploading a special
text/html file into the root directory of the domain name.
 DNS-based validation - For this validation method you need to
create a certain CNAME record in the DNS settings of your domain.
 Email Validation – Users will be validated by an email that belongs
to the domain

9. Email based authentication
 Until late 2015 the email addresses that were allowed to
be specified by the CA. This might be an interesting
problem
 Cert Vulnerability note 591120 (March 27th 2015)
 Multiple SSL certificate authorities use predefined email addresses
as proof of domain ownership
 16 certificate authorities were listed as affected (others unknown)
 What is the problem
 If an admin is not aware of sensitive email addresses and assigns
them this can lead to a certificate being issued for their domain

10. Problem Children
 admin@yourdomain.com
 administrator@yourdomain.com
 webmaster@yourdomain.com
 ssladmin@yourdomain.com
 root@yourdomain.com
 hostmaster@yourdomain.com
 postmaster@yourdomain.com
 ssladministrator@yourdomain.com
 it@yourdomain.com

11. The Fix
 Most documents including the Mozilla CA Certificate Inclusion Policy
and the CA/Browser baseline requirement documents the addresses
that can be used should be limited to those specified in RFC2142
 MAILBOX NAMES FOR COMMON SERVICES, ROLES AND FUNCTIONS
 The only exception is also the domain listed in the WHOIS contact
 This largely solved the underlying problem but every CA in existence
needs to update their policies otherwise the issue isn’t fixed
 This is mostly a problem where people can choose their own email
registration names or they are given based on a known theme. Hence
the title.

12. The problem shown.

13. An exercise best left to the reader
 Now all you would have to do is find a CA that still allows
registering that email address and poof mail.rit.edu SSL
cert.

14. With the update

15. What are these addresses
 PostMaster@example.com
 Reserved for SMTP
 Hostmaster@example.com
 Reserved for DNS
 Webmaster@example.com
 Reserved for Web

16. The new problem
 Not everyone realizes that these addresses must be
registered when setting up a webserver that will use SSL
 Or email that will use SSL, etc.
 These email addresses are not well known. For instance
hostmaster is no a widely recognized email address

17. A New Twist on a New Problem
 If these are registered then we are fine.
 But is there a situation where we might still be able to
access other peoples email?
 Where individuals might forget about this concept?
 Enter Bill Stackpole

18. Anonymous email access

19. Breaking the bank
 Mailinator is actually the only one I haven’t broken yet.
 Well this isn’t strictly speaking true…
 However often these are so simple where I can just search
hostmaster@xyz.com

21. Other issues
 Often these are slightly more secure and require that I be
clever.
 However…
 Often these systems will try and be intelligent about their email
address understand, but not about security
 For instance, spaces, dots, null characters, etc.

22. Just a few off my hit list

23. Recently in the news

24. General Fixes
 Don’t allow email verification
 Communication among CAs would prevent this
 It will also help security as a whole
 Pinning certificates