SummaryAEZ is a block cipher mode based on AES which uses three 128‐bit keys. The algorithm has been updated several times during the three rounds of the CAESAR cryptographic competition. Cryptanalytic results presented on AEZ to date do not breach its security. This paper describes a fault injection analysis on AEZ. We focus on analysing AEZ v4.2 but also investigate the applicability of these analyses to the recent version AEZ v5. This paper shows that all three 128‐bit keys in AEZ v4.2 can be uniquely retrieved using only three random‐valued single byte fault injections. A similar approach using four fault injections can uniquely recover all three keys of AEZ v5. The feasibility of this fault injection methodology has been proven against AES in previous works.