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Google open sources web app security scanner

Skipfish released from captivity

Google has released an open source security scanner designed to seek out holes in, yes, web applications.

Dubbed Skipfish, this web app "security reconnaissance tool" generates an interactive map of an application based on checks for certain security flaws, involving everything from self-signed SSL certificates to server-side SQL and XML injection. It performs a recursive crawl of a site, but it can also probe a list of pre-defined links.

In a post to the Skipfish wiki, Google's Michal Zalewski describes the tool as something similar to the open source Nikto scanner or the now commercial Nessus scanner from Tenable Network Security. But he claims that Google's scanner is particularly fast and particularly easy to use.

Built with pure C code and equipped with a customized http stack, Skipfish can bombard an application with more than 2,000 http requests a second over local and metropolitan area networks, according to Zaleswki. And it has reached more than 7,000 requests a second, he says, on local instances.

But Zaleswki warns that Skipfish is "no silver bullet" and that it may be "unsuitable for certain purposes". It does not satisfy the requirements of the Web Application Security Consortium's Web Application Security Scanner Evaluation Criteria - "some of them on purpose, some out of necessity," he says. It doesn't check applications against a database of known vulnerabilities. And it doesn't check for buffer overflows, full-fledged Javascript cross-site scripting, or flaws involving Java, Flash, and other third-party, plug-in-based content.

Larry Suto, a freelance security consultant who specializes in web applications, has spent less than a day with the new scanner, but he expects that - this being a Google tool - Skipfish will be particularly adept at crawling, something you can't expect from other scanners.

"Crawling is difficult to get right," Suto tells The Reg. "And given Google's history, I expect very interesting things on the crawling front."

But he warns that judging from Google's documentation, the tool may have problems with sites that use complex Javascript structures. He's also wary that the tool doesn't include a database of existing attacks.

Skipfish is open sourced under the Apache 2 license, and it should support Linux, FreeBSD 7.0+, MacOS X, and Windows. You can download it here. ®

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