STE WILLIAMS

Attacks on IE drive-by bug go wild

Microsoft on Tuesday warned that attackers have begun exploiting a critical vulnerability in Internet Explorer and rolled out a temporary fix until a permanent patch is issued.

The vulnerability in IE versions 6, 7 and 8, which involves the way the browser handles cascading style sheets, allows adversaries to perform drive-by malware attacks by luring victims to booby-trapped webpages. The exploits are triggered by recursive CSS pages, in which style sheets include their own addresses.

Microsoft confirmed the security flaw in late December. On Tuesday, it updated its advisory to reflect “reports of limited attacks attempting to exploit a vulnerability in all supported versions of Internet Explorer.”

Redmond also issued a workaround that large organizations can implement to protect themselves until a patch is released. It comes in the form of a Fix it that causes IE to reject CSS pages that contain the same URL as a style sheet that’s trying to load it.

“This change causes Internet Explorer to refuse to import a CSS style sheet if it has the same URL as the CSS style sheet from which it is being loaded,” Microsoft Security Response Center’s Keven Brown explained here. “Simply put, the workaround inserts a check to see if a style sheet is about to be loaded recursively, and if it so, it aborts the load of the style sheet.”

For the workaround to be effective, all existing security updates, particularly MS10-090 released on December 14, must be installed. The temporary fix causes a minor performance decrease – adding about 150 milliseconds to the browsers’ startup time – so it should be uninstalled once a patch is put in place. Third-party apps that work with IE should be thoroughly tested before putting the workaround into effect.

The workaround came on the first Patch Tuesday of 2011. As part of the regularly scheduled update release, Microsoft also issued two updates, one in the Windows Backup Manager and the other in Microsoft Data Access Components.

While it was one of the smallest Patch Tuesdays ever, it failed to address at least known vulnerabilities that put Microsoft users at risk. One of them allows attackers to remotely execute malicious code on machines running the XP, Server 2003, Vista, and Server 2008 versions of Windows. Exploit code for it is publicly available. The other, disclosed by Google researcher Michal Zalewski, leads to what he said was a “clearly exploitable crash.” ®

Popular sites caught sniffing user browser history

Boffins from Southern California have caught YouPorn.com and 45 other sites pilfering visitors’ surfing habits in what is believed to be the first study to measure in-the-wild exploits of a decade-old browser vulnerability.

YouPorn, which fancies itself the YouTube of smut, uses JavaScript to detect whether visitors have recently browsed to PornHub.com, tube8.com and 21 other sites, according to the study. It tracked the 50,000 most popular websites and found a total of 46 other offenders, including news sites charter.net and newsmax.com, finance site morningstar.com and sports site espnf1.com.

“We found that several popular sites – including an Alexa global top-100 site – make use of history sniffing to exfiltrate information about users’ browsing history, and, in some cases, do so in an obfuscated manner to avoid easy detection,” the report states. “While researchers have known about the possibility of such attacks, hitherto it was not known how prevalent they are in real, popular websites.”

To cover its tracks, YouPorn encodes its JavaScript to hide the sites it searches for and decodes it only when used. Other websites dynamically generate the snoop code to prevent detection by simple inspection. Still others rely on third-party history-stealing libraries from services that include interclick.com and meaningtool.com.

The scientists detected the history stealing by concocting their own version of Google’s Chrome browser with a JavaScript information flow engine that “uses a dynamic source-to-source rewriting approach.”

The 46 sites exploit a widely known vulnerability that currently exists in all production version browsers except of Apple’s Safari, which earlier this year became the first major browser to insulate users against the threat. Google Chrome, which is based on the same Webkit engine, soon followed. Beta versions of Mozilla Firefox and Microsoft Internet Explorer also fix the problem, but production versions of those browsers are still wide open.

The exploit works by using JavaScript to read cascading style sheet technologies included in virtually every browser that causes visited links to appear in purple rather than blue. Developers have known of the weakness for a decade or more but until recently said it couldn’t be easily repaired without removing core functionality.

The study also detected code on sites maintained by Microsoft, YouTube, Yahoo and About.com that perform what the scientists called “behavioral sniffing.” They employ JavaScript that covertly tracks mouse movements on a page to detect what a user does after visiting it.

A PDF of the paper, which was written by Dongseok Jang, Ranjit Jhala, Sorin Lerner, and Hovav Shacham, is here. ®

  • 06/12/2010
  • adm