Although the Wireless M-Bus Security mode 5 employs shared AES key, we did not receive any key in the box with the meter. The meter cannot receive any data as indicated at the protocol level. We do not see any port that can be used to change the AES key. It seems likely that the meter depends on a shared key or a key derived from the number of the meter so the software offered by Kaden can read the meter. In such case, the confidentiality of the water metering is endangered as an adversary only needs a compatible reader to read the consumption.
Base score 6.5 (Medium severity)
An adversary needs to be in a vicinity of the meters (tens of meters, with a good antenna probably more).
An adversary needs publicly available reading set offered by Kaden such as KADEN ZET810s.
None. An adversary can correlate the position of the meters with the signal strength.
The meter identifier is sent in each message and it is readable on the front of the meter. A cooperating users can make the task for the adversary easier when they let the adversary see the meter or tell the meter number. Such cooperation is not necessary to carry an attack.
The adversary can learn all information that a vulnerable meter sends.
CWE-798: Use of Hard-coded Credentials
The encryption key of the meters is probably not configurable. You should replace the meters.