Safety in the cloud(s): 'Vaporizing' the Web application firewall to secure cloud computing
by Alex Meisel - Art of Defence - Thursday, 23 July 2009.
Defining the distributed Web application firewall (dWAF) for cloud protection

Web application security in a cloud has to be scalable, flexible, virtual and easy to manage. A WAF must escape hardware limitations and be able to dynamically scale across CPU, computer, server rack and datacenter boundaries, customized to the demands of individual customers. Resource consumption of this new distributed WAF must be minimal and remain tied to detection / prevention use instances rather than consuming increasingly high levels of CPU resources. Clouds come in all sizes and shapes, so WAFs must as well.

The dWAF must be able to live in a wide variety of components to be effective without adding undue complexity for cloud service providers. Todayís providers are using a variety of traditional and virtual technologies to operate their clouds, so the ideal dWAF should accommodate this mixed environment and be available as a virtual software appliance, a plug-in, SaaS or be able to integrate with existing hardware. Flexibility with minimal disruption to the existing network is central.

A web-based user interface must allow customers to easily administrate their applications. Configuration should be based on the applications under protection, not defined by a singular host, allowing far more granular settings for each application. Ruleset configuration must be supported by setup wizards. Statistics, logging and reporting has to be intuitive and easy to use and must also integrate seamlessly into other systems. Most importantly for a dWAF, multi-administrator privileges must be made available and flexible enough to effectively manage widely divergent policy enforcement schemes. Cloud providers should look for a set of core protections.

Detection and protection

Foundational security using black, white and grey listings for application requests and responses must be possible. To make sure pre-set policy enforcements are not activated or deactivated without approval from an administrator, deployment and policy refinement through establishing rulesets must be possible in a shadow monitoring or detection only mode. Once the shadow monitoring ruleset is stable, only then should it be allowed to deploy in an enforcement mode on the dWAF. This allows complete transparency for the administrator into the real-world effect of this ruleset, while at the same time allowing layered rulesets to be tested without compromising existing policy enforcement. Avoiding false positives and relaxed established defenses are essential for a real-world, usable dWAF in a cloud.

Automated learning and ruleset suggestions based on intelligent algorithms or recommendations from a static source code analyzer or web vulnerability scanner are also desirable from a manageability view. Again, this only holds true if the administrator retains full control over activation / deactivation of each ruleset. Without this control, wanted traffic may become blocked and policy settings would become compromised.

Application shielding

Pro-active security functions are highly recommended to reinforce any application in a cloud. Detection is simply not enough for todayís web application security. Features like transparent secure session management, URL encryption and form-field virtualization will provide strong deterrence to attack, while saving application development and deployment time. These features are effective because session management, URL encryption and form-field virtualization is done at the dWAF level and not in the application itself.

An authentication framework support that enables businesses to consolidate their applications under one management schema is also desirable for a dWAF. This enables users to handle the authentication in front of their applications rather than behind, which adds another perimeter of security. A consolidation of all applications with dedicated rights-management ability is also a strong usability function that will make an administratorís life easier.


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