The Ultimate Gift Cards for WooCommerce WordPress plugin before 3.2.10 does not verify that the user redeeming a gift card is its intended recipient, allowing any authenticated user, such as a subscriber, to redeem gift cards belonging to other users, zeroing their balance and crediting the value to themselves.
In 3.2.9 an ownership check was added on one of the two affected redemption paths; the one that remains requires a companion Ultimate Gift Cards for WooCommerce WordPress plugin before 3.2.10 from the same vendor to be active.