We conduct a security analysis of the e-voting protocol used for the largest political election using e-voting in the world, the 2022 French legislative election for the citizens overseas. Due to a lack of system and threat model specifications, we built and contributed such specifications by studying the French legal framework and by reverse-engineering the code base accessible to the voters. Our analysis reveals that this protocol is affected by two design-level and implementation-level vulnerabilities. We show how those allow a standard voting server attacker and even more so a channel attacker to defeat the election integrity and ballot privacy due to 6 attack variants. We propose and discuss 5 fixes to prevent those attacks. Our specifications, the attacks, and the fixes were acknowledged by the relevant stakeholders during our responsible disclosure. Our attacks are in the process of being prevented with our fixes for future elections. Beyond this specific protocol, we draw general conclusions and lessons from this instructive experience where an e-voting protocol meets the real-world constraints of a large-scale and political election. Responsible Disclosure and Acknowledgments We conducted this security analysis through passive analysis only; we never attacked voting servers. Therefore, we could not alter the integrity or the security of the election. Moreover, all the vulnerabilities reported in this document have been reported to the relevant stakeholders at least 3 months before publication. We thank those stakeholders, i.e., Europe and Foreign Affairs French Ministry (EFA French Ministry), Agence nationale de la sécurité des systèmes d'information (ANSSI), Voxaly Docaposte, and the researchers running the 3 rd-party services (Stéphane Glondu, Pierrick Gaudry, and Véronique Cortier) for their help and discussions after we sent them our findings. In particular, we would like to thank again the role of ANSSI in the responsible disclosure process, which has always be a key player in promoting transparency and openness. This is greatly appreciated given the context of this work. Finally, we would like to thank our colleagues Myrto Arapinis, Hugo Labrande, and Emmanuel Thomé for their help to collect data about the French Legislative E-Voting Protocol (FLEP).