Kasa EC71 v4 and EC70 v4 firmware contains a static cryptographic private key stored in a read-only filesystem that is shared across devices

Kasa EC71 v4 and EC70 v4 firmware contains a static cryptographic private key stored in a read-only filesystem
that is shared across devices.  An
attacker with access to the firmware image can extract the embedded key. 

Successful
exploitation may allow an unauthenticated attacker on the same network to use
this key in the web management service, compromising the confidentiality of
encrypted communications. This may enable passive decryption of traffic or
active man-in-the-middle (MITM) attacks