Conn. Gen. Stat. § 12-51: List may be filed by holder of encumbrance.

The holder of any encumbrance on, or interest in, any real estate which is subject to taxation and the owner of which has failed to give in the list thereof for the purposes of taxation, in the manner and within the time prescribed by this chapter, may, personally or by his authorized agent or attorney, file such list in the name of the record owner, within ten days after the expiration of the time limited to such record owner, and without the amount of the statutory penalty for failure to file such list being added thereto. If such list is filed by such authorized agent or attorney, such agent or attorney shall make oath that he is authorized by his principal to sign, execute and file such list and that he has knowledge of the facts therein set forth.