TITLE:
Cisco ASA Failover Denial of Service Weakness

SECUNIA ADVISORY ID:
SA17550

VERIFY ADVISORY:
http://secunia.com/advisories/17550/

CRITICAL:
Not critical

IMPACT:
DoS

WHERE:
>From local network

OPERATING SYSTEM:
Cisco ASA 5500 Series Adaptive Security Appliances
http://secunia.com/product/6115/
Cisco PIX 7.x
http://secunia.com/product/6102/

DESCRIPTION:
Amin Tora has reported a weakness in Cisco ASA (Adaptive Security
Appliances), which can be exploited by malicious people to cause a
DoS (Denial of Service).

The weakness is caused due to the ASA failover testing algorithm
failing to properly identify that the active firewall has failed. The
standby firewall performs failover tests by sending ARP requests for
the active firewall's IP addresses. This can be exploited to prevent
the standby firewall from activating via spoofed ARP responses. The
failover may also fail to happen if there is another device with the
same IP address as the active firewall on the same network subnet.  

The weakness has been reported in ASA running 7.0(0), 7.0(2), and
7.0(4).

SOLUTION:
The vendor recommends that port security should be configured for all
switch ports in the same VLANs as the active and standby firewalls
enabled interfaces to prevent an attacker from spoofing the active
firewall's interface MAC address.

The firewall log should also be monitored for any IP address
collisions.

PROVIDED AND/OR DISCOVERED BY:
Amin Tora, ePlus Security Team.

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