The company said it removed the backdoor which had been discovered in the RackSwitch and BladeCenter switches.
"An authentication bypass mechanism known as 'HP Backdoor' was discovered during a Lenovo security audit in the Telnet and Serial Console management interfaces, as well as the SSH and Web management interfaces under certain limited and unlikely conditions," it said.
"This bypass mechanism can be accessed when performing local authentication under specific circumstances using credentials that are unique to each switch. If exploited, admin-level access to the switch is granted."
An audit of the source code changes showed that the backdoor was added in 2004 when ENOS was owned by Nortel's Blade Server Switch Business Unit, at the request of a BSSBU OEM customer.
Nortel spun off BSSBU in 2006 to form BLADE Network Technologies which was purchased by IBM in 2010, and, subsequently, Lenovo in 2014.
"Lenovo has provided relevant source code to a third-party security partner to enable independent investigation of the mechanism," the company added.