Software Engineering Institute

The Cisco Adaptive Security Appliance (ASA) is firewall that includes routing and intrusion prevention system (IPS) features. The Cisco PIX is a stateful firewall. The Cisco ASA and PIX firewalls include the ability to use LDAP and AAA servers to authenticate remote users or terminate VPN connections.

Per Cisco Security Advisory cisco-sa-20070502-asa:
Cisco ASA and PIX devices leveraging LDAP AAA servers for authentication of terminating L2TP IPSec tunnels or remote management sessions may be vulnerable to an authentication bypass attack. See the following bullets for more details:

• Layer 2 Tunneling Protocol (L2TP)
  Devices terminating L2TP IPSec tunnels must be configured to use LDAP in conjunction with CHAP, MS-CHAPv1, or MS-CHAPv2 authentication protocols to be vulnerable. If LDAP authentication is used in conjunction with PAP, the device is not vulnerable to the LDAP L2TP authentication bypass.
  
• Remote Management Access
  Cisco ASA and PIX devices leveraging LDAP AAA servers for authentication of management sessions (telnet, SSH and HTTP) may be vulnerable to an authentication bypass attack. Access for management sessions must be explicitly enabled and is limited to the defined source IP address within the device configuration.

A remote, unauthenticated attacker may be able to gain access to internal resources, or gain direct access to the firewall.

Upgrade Cisco has released an update to address this vulnerability. See the Software Versions and Fixes section of Cisco Security Advisory cisco-sa-20070502-asa for more details.

Restrict access

Restricting access to the firewall's telnet, SSH and HTTP interfaces to trusted hosts by using IP access control lists may mitigate this vulnerability.