Aapo Oksman

Senior Security Specialist at Nixu Corporation

Aapo Oksman


certmitm: automatic exploitation of TLS certificate validation vulnerabilities

TLS is the de facto way of securing network connections. It provides an easy way of ensuring confidentiality, integrity and authentication for any type of communication. However, like most things in life, this is also too good to be true.

TLS allows communicating parties to uniquely authenticate each other by validating each other's certificate. However, many TLS libraries and frameworks have insecure default settings or allow for the developers to skip important aspects of certificate validation in their client implementations.

This talk explores issues in TLS client certificate validation and the underlying reasons why developers still fail to implement TLS correctly. Most importantly, we hack all the things with a new TLS mitm tool: certmitm.

certmitm automatically discovers and exploits insecure certificate validation vulnerabilities in TLS clients. Let's use the tool to hack iOS, Windows 11 and more while we deep dive into the world of insecure TLS certificate validation.


Aapo Oksman is a Senior Security Specialist at Nixu Corporation working with application, network and device security. His background is in electrical engineering, embedded devices, and test automation. Combining his background with a hobby in hacking lead to a career in cybersecurity focusing on industrial IoT.

In his free time, Bug Bounties and security research keep Aapo motivated and learning. His work in PKI and TLS has resulting in multiple CVEs from vendors such as Microsoft and Apple. Outside work and research Aapos passion is in the community. He takes part in organizing local security meetups and coaches the Finnish national youth CTF team to the yearly European Cybersecurity Challenge competition.