The company confirmed the vulnerability in its Lightweight Extensible Authentication Protocol (LEAP), which allows hackers to launch dictionary attacks for guessing passwords for wireless LAN access.
The company is recommending customers use a new security protocol, Extensible Authentication Protocol-Flexible Authentication via Secure Tunneling (EAP-FAST), which it said reduces the threat of attack.
A dictionary attack compares a huge catalogue of words with the target computer until it finds a matching password. The LEAP protocol reduces the number of possible matches, which makes the attack faster
Cisco's advice comes after software expert Joshua Wright developed a tool for launching the attack against LEAP.
Wright waited to release the tool until Cisco was able to fix the problem.