mTLS: when certificate authentication done wrong

Although x509 certificates have been here for a while, they have become more popular for client authentication in zero-trust networks in recent years. Mutual TLS, or authentication based on X509 certificates in general, brings advantages compared to passwords or tokens, but you get increased complexity in return. In this talk, we’ll deep dive into some novel attacks on mTLS authentication. We won’t bother you with heavy crypto stuff, but instead we’ll have a look at implementation vulnerabilities and how developers can make their mTLS systems vulnerable to user impersonation, privilege escalation and information leakages. We present some CVEs we found in popular open-source identity servers and ways to exploit them. Finally, we’ll explain how these vulnerabilities can be spotted in source code and how the safe code looks like.