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Bad firewall practice helps DDoS attacks

Firewalls and IPS put in wrong place on networks

The rising tide of distributed denial of service attacks (DDoS) is being made much worse by a tendency to mis-deploy firewalls and intrusion prevention systems (IPS) in front of servers, a report by Arbor Networks has found.

The company surveyed 111 global service providers across fixed and mobile sectors for its 2010 Infrastructure Security Report and uncovered a huge jump in DDoS attack size during the year. Maximum attack sizes reached 100Gbit/s for the first time, double that for 2009, and ten times the peak size seen as recently as 2005, increasingly in the form application attacks rather than simple packet flooding.

Attack frequency also appears to be increasing, with 25 percent of respondents seeing 10 or more DDoS attacks per month, and 69 percent experiencing at least one.

But according to Arbor, service providers and corporate could significantly reduce their DDoS vulnerability by designing their security infrastructure to better locate policy-based security devices such as firewalls.

During 2010, nearly half of all respondents had experienced a failure of their firewall or IPS due to DDoS, something that could have been avoided in many cases using better router security configuration.

“They [firewalls] should not be placed in front of servers. Folks do it because they have been programmed to do it,” says Arbor’s solutions architect, Roland Dobbins. In many cases, these devices became immediate bottlenecks in the face of DDoS, achieving the attackers' aims with ease.

Firewalls and IPS were fine for LANs where they filtered outgoing traffic, but turned into obvious points of failure when used as a barrier to protect servers receiving large volumes of inbound packets, he says.

One thing that is clear form Arbor’s report is that DDoS size will go on increasing, fed ironically by increased investment in defences against DDoS generally. Rather like the growth in spam after the advent of efficient filtering, better defences force attackers to up their game, throwing more and more traffic at targets in the hope of having some effect.

An interesting blind spot suggested by Arbor could be mobile networks, which Dobbins describes as being almost “accidental ISPs.”

Currently, mobile providers know almost nothing about the state of the handsets using their services, despite half reporting security problems with customers. The same proportion reported outages due to security incidents, which suggests that such networks could become the next frontier for criminals to attack Internet targets.

“They don’t have visibility into their IP network. They are almost a decade behind,” says Dobbins of providers in this space.

Longer term, a missing piece of the DDoS defence is policing, witha significant minority of respondents expressing a lack of confidence in law enforcement. Many of the sceptical see no point in reporting attacks to the law and have little hope of it doing much good even when they do.


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