Summary In this advisory we are disclosing a signature verification bypass vulnerability in the Huawei recovery mode. The vulnerability can be used not only to apply unauthentic firmware updates but also to achieve arbitrary code execution in the recovery mode. Combining this advisory with the vulnerability detailed in CVE-2021-40055, an attacker can achieve remote code execution without user interraction from the position of a network MITM. The vulnerability was fixed in February 2022. Vulnerability Details Huawei devices - both those running Android and those running HarmonyOS - implement a proprietary update solution which can be applied in various ways. The methods are all public and differ in how the process is triggered (manually or automatically) and how the update media file to be applied is supplied (downloaded over Wi-Fi or supplied from a memory card).