TL-WR845N(UN)_V4_200909 and TL-WR845N(UN)_V4_190219 was discovered to contain a hardcoded password for the root account which can be obtained by analyzing downloaded firmware or via a brute force attack through physical access to the router.
TL-WR845N(UN)_V4_201214, TP-Link TL-WR845N(UN)_V4_200909, and TL-WR845N(UN)_V4_190219 was discovered to transmit user credentials in plaintext after executing a factory reset.
TP-Link TL-WR845N(UN)_V4_201214, TL-WR845N(UN)_V4_200909 and TL-WR845N(UN)_V4_190219 were discovered to contain weak default credentials for the Administrator account.