Public attack code aimed at Windows Web servers works, says Symantec

Researchers not surprised at the quick appearance of denial-of-service exploit

Researchers at Symantec yesterday confirmed that working attack code published Jan. 6 can cripple Web servers running Microsoft's ASP .Net.

The proof-of-concept exploit was published last Friday on GitHub, a site that hosts software projects, and has been used in the past by hackers to distribute their work.

Other security experts were not surprised that attack code appeared within days of Microsoft rushing out a patch for a denial-of-service vulnerability in its software.

"No, not surprising at all," Andrew Storms, director of security operations at nCircle Security, said in an interview Tuesday. "There was enough interest [in the researchers' original presentation] that we should have expected exploit code soon."

The presentation Storms referred to was made by German researchers Alexander Klink and Julian Walde on Dec. 28 at the Chaos Communication Congress (CCC) conference in Berlin, where they demonstrated a flaw in the Web's most popular application and site programming languages, including Microsoft's ASP .Net, the open-source PHP and Ruby, Oracle's Java and Google's V8 JavaScript.

According to Klink and Walde, attackers could cripple Web servers by conducting denial-of-service attacks using a single off-the-shelf PC and a low-bandwidth connection to the Internet.

In a security advisory issued the same day, Microsoft promised to patch the vulnerability in ASP .Net, then followed that on Dec. 29 with its first "out-of-band" update of 2011.

On Jan. 6, someone identified as "HybrisDisaster" published the attack code on GitHub.

The interval between the Klink-Walde presentation and the appearance of attack code was just nine days, and eight days after Microsoft released its emergency patch.

"Their presentation was pretty good and illustrated the vulnerability and how to exploit it very well," said Wolfgang Kandek, chief technology officer at Qualys. Like Storms, Kandek wasn't stunned that exploit code showed up so quickly. "[The attack] really has a pretty simple mechanism," Kandek added, "so actually, no, I'm not surprised."

The proof-of-concept, which is in fact a massive text file, can simply be sent to a vulnerable Web server to cripple it, added Tod Beardsley, a researcher at Rapid7, the company that produces the popular Metasploit penetration testing toolkit.

While researchers weren't shocked to see exploit code appear so quickly, neither was Microsoft. When the company shipped its ASP .Net patch two weeks ago, a pair of Microsoft engineers said they "anticipate the imminent public release of exploit code" as they explained why a patch was released outside the normal schedule.

(By design, Microsoft gives all denial-of-service vulnerabilities an exploitability index rating of "3" -- the lowest possible rating -- essentially making that rating worthless for DoS bugs.)

"Microsoft going out-of-band on this is a good clue to how bad this vulnerability could be," said Jason Miller, director of research and development at VMware, in a Tuesday interview.

Miller said that attackers may use the published exploit code, with the most likely culprits hackers motivated by non-financial reasons. Crippling a major website would be a coup to attackers interested only in notoriety, Miller argued.

That description may fit HybrisDisaster, who used a catchphrase linked to the loose-knit hacktivist group dubbed "Anonymous" in the text that accompanied the ASP .Net exploit.

"We are Legion. Expect us," HybrisDisaster wrote.

Anonymous has used denial-of-service attacks previously in several of its disruptive campaigns.

The ASP .Net patch was delivered as part of Microsoft's MS11-100 security update, which has been available through the usual Windows Update and Windows Server Update Service (WSUS) channels since Dec. 28.

A video of the Klink-Walde CCC presentation is available on YouTube.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer , on Google+ or subscribe to Gregg's RSS feed . His e-mail address is .

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This story, "Public attack code aimed at Windows Web servers works, says Symantec" was originally published by Computerworld.

Copyright © 2012 IDG Communications, Inc.

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