Spoofed Web Certificates

A research team at the Fraunhofer Institute for Secure Information Technology SIT in Darmstadt, Germany, has found a way to issue fraudulent website certificates that are used to ensure trustworthiness of Internet domains.

The team lead by Dr. Haya Shulman has shown that the weakness in the domain validation can be exploited in real life and that the security of Internet infrastructures needs to be improved. To do so the researchers have informed Web CAs (Certificate Authorities) and suggest a new method and implementation that Web CAs may use to mitigate the attack. Further information at https://www.sit.fraunhofer.de/en/dvpp/

Web certificates are the basis of the SSL/TLS protocol which protects most web sites, such as online mail and office apps, online retailing and online banking. If a web site presents a valid certificate, the user’s browser will signal to the user that the web site’s identity is verified and can be trusted, e.g. by showing a green padlock.

The research team at Fraunhofer SIT showed that this trust is actually ill-founded and users can easily be tricked into sending their secret passwords and data to fraudulent phishing web sites.

Certificates are issued by so-called Web CAs, and virtually all popular Web CAs are using a method called Domain Validation (DV) to verify a web site’s identity before issuing a certificate to that web site. The Fraunhofer team demonstrated that Domain Validation is fundamentally flawed, and consequently they could trick many Web CAs into issuing fraudulent certificates.

A cybercriminal could use this attack to obtain a fraudulent certificate, e.g., for a popular online retailer, set up a web site that perfectly mimics that online retailer’s store, and then phish usernames and passwords.

The Fraunhofer team led by Dr. Haya Shulman exploited a number of well known vulnerabilities in the Domain Name System (DNS), which is the Internet’s yellow pages mapping domain names to Internet addresses. Cybersecurity researchers were well aware of these vulnerabilities in the DNS and their potential impact on Domain Validation, but so far this was considered a rather theoretical risk and something only very powerful, e.g., nation state-level attackers could exploit.

The team demonstrated for the first time that this risk is actually very real. “While the details of our attack are technically quite sophisticated, executing the attack does not require any specific compute power or any capability to intercept Internet traffic. Nothing more is needed than a laptop and an Internet connection.” says Dr. Haya Shulman of Fraunhofer SIT.

The team informed German security authorities and Web CAs. As a mitigation the researchers developed an improved version of DV, called DV++, which could replace DV without any further modifications and which is provided free of charge here: https://www.sit.fraunhofer.de/en/dvpp/ . A research paper describing the details of this attack as well as DV++ will be presented at the ACM Conference on Computer and Communications Security (ACM CCS) in Toronto, Canada, in October 2018.

Dr. Haya Shulman, Prof. Michael Waidner