On Hoermann BiSecur devices before 2018, a vulnerability can be exploited by recording a single radio transmission. An attacker can intercept an arbitrary radio frame exchanged between a BiSecur transmitter and a receiver to obtain the encrypted packet and the 32-bit serial number. The interception of the one-time pairing process is specifically not required. Due to use of AES-128 with an initial static random value and static data vector (all of this static information is the same across different customers' installations), the attacker can easily derive the utilized encryption key and decrypt the intercepted packet. The key can be verified by decrypting the intercepted packet and checking for known plaintext. Subsequently, an attacker can create arbitrary radio frames with the correct encryption key to control BiSecur garage and entrance gate operators and possibly other BiSecur systems as well ("wireless cloning"). To conduct the attack, a low cost Software Defined Radio (SDR) is sufficient. This affects Hoermann Hand Transmitter HS5-868-BS, HSE1-868-BS, and HSE2-868-BS devices.