In the years leading to the definition of TLS 1.3, many vulnerabilitieshave been published on the TLS protocol, including numerous implementationflaws affecting a wide range of independent stacks. The infamous Heartbleedbug, was estimated to affect more than 20 % of the most popular HTTPS servers.We propose a structured review of these implementation flaws. By consideringtheir consequences but also their root causes, we present some lessons learned oryet to be learned. We also assess the impact of TLS 1.3,the latest version of theprotocol, on the security of SSL/TLS implementations.