F5 Networks Files Patent Lawsuit Against WAF Vendor Imperva

In a rare patent infringement cases involving Web application security, F5 Networks is suing Imperva for allegedly using its patented application security technology in Imperva's Web application firewall and other security products.

F5's patent suit, which the networking and security company filed on May 4, calls for both a preliminary and permanent injunction barring Imperva and others from developing, selling -- and using -- its Secure Sphere and other products that infringe on F5's so-called "Method and System for Extracting Application Protocol Characteristics" patent, which was awarded by the U.S. Patent and Trademark Office in 2001. The patent, number 6,311,278, is also referred to as the "'278 patent" in F5's filing.

The lawsuit calls for Imperva to pay F5 for "damages to compensate F5 for the infringement that has occurred," as well as court and attorney costs. "Imperva's acts of infringement have caused, and will continue to cause, substantial and irreparable injury to F5 and its rights," the F5 patent suit says. "On information and belief, Imperva committed such infringement with knowledge of the '278 patent, and such infringement was committed willfully."

[UPDATE: 5/12/10]: Imperva issued a statement today calling the lawsuit "baseless," saying that F5 turned to litigation after its WAF didn't sell well. "A few years ago, F5 began to sell its web application firewall. Few bought it, choosing instead Imperva's superior product. Unable to compete on the merits, F5 now reverts to litigation, asserting an old 1999 patent. Imperva doesn't use—or need—F5's technology," Imperva said in its statement.

"Imperva will vigorously contest this matter on behalf of itself and its customers," it said.

F5, meanwhile, provided a brief statement earlier in the week: "F5 thinks it is appropriate to take reasonable measures to defend our intellectual property rights. However, it is our current policy not to comment on pending litigation."

This isn't the first patent dispute over Web application security technology. In August 2007, Cenzic sued SPI Dynamics, now part of HP, for using its patented "fault injection" technology. SPI also filed a suit against Cenzic, and in October Cenzic and HP/SPI settled the legal matter with a cross-licensing agreement.

The patented security technology in dispute in the F5 and Imperva case is "directed generally at methods and systems for defining a set of allowable actions regarding a network application," says F5's filing with the U.S. District Court for the Western District of Washington in Seattle.

Robert Hansen, a.k.a. "RSnake" and founder of SecTheory, says F5's patented technology basically identifies which protocol the client is using to communicate with the server and defines which protocols are allowed, or not: "So if someone were to put a Web server on Port 23, it would be good if the WAF could identify that it's not an FTP server but a Web server, for example," Hansen says. "And certain methods like GET and POST might be [allowed], but PUT and DELETE would not be," for instance, he says.

The technology could also identify things like cross-site scripting (XSS) or cross-site request forgery (CSRF) attacks, he says.

Hansen says if Imperva loses the case, it's likely it would have to modify its products by removing protocol detection altogether, or performing that function using a different method. "I just hope things like this [lawsuit] don't negatively impact innovation" in Web security, he says.

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