Networking equipment maker Cisco Systems has warned its customers about security holes in two products that provide user authentication and authorisation services for network devices.

The company has issued a security advisory identifying "multiple Denial of Service (DoS) and authentication related vulnerabilities" in two products: the Cisco Secure Access Control Server for Windows (Windows ACS) and Cisco Secure Access Control Server Solution Engine (Secure ACS). The vulnerabilities could allow attackers or malicious users to crash the ACS products or gain unauthorised access to network devices, Cisco said.

ACS products centralise user identity management for other Cisco products and management applications, allowing administrators to manage and enforce access policies that control who can log into the network.

Cisco found that both the Secure ACS and ACS Windows products stopped responding to new TCP connections after being flooded with TCP connections on port 2002. The denial of service condition hampered the ACS devices' ability to process authentication requests and required the ACS devices to be rebooted to restore authentication services, Cisco said.

In other instances, Cisco found that, under certain circumstances attackers that faked (or "spoofed") the network address of a computer that is accessing the ACS administrative user interface could access that interface without being asked to log in first, Cisco said.

Cisco released product upgrades for ACS Windows version 3.2 and 3.3 and for the ACS Solution Engine.