According to researchers from Stanford University and Carnegie Mellon, their first-ever study of the privacy mode in browsers found multiple weaknesses, which attackers could exploit to reconstruct a browser's true history. The researchers plan to present their findings at this week's Usenix Security Symposium in Washington.
To assess the security of browsers' privacy modes, the researchers examined privacy controls, cookie controls, and object controls in Firefox 3.5, Internet Explorer 8, Google Chrome, Apple Safari 4, and Opera 10. They also evaluated numerous add-ons, including CookieSafe for cookie controls in Firefox, AdBlock Plus for controlling objects -- such as suppressing banner advertisements from displaying -- in Firefox, and PithHelmet for Safari object control.
What the researchers found were numerous vulnerabilities in how these browsers and add-ons approach privacy. As a result, "current private browsing implementations provide privacy against some local and web attackers, but can be defeated by determined attackers," they said.
For example, browsers sometimes leak information when in private mode. For starters, any Certificate Authority (CA) certificates cached when a user is in private mode persist when they switch out of private mode. "This is significant privacy violation," according to the researchers.
When it comes to browser privacy, or lack thereof, the researchers also cautioned that more flaws and vulnerabilities could exist, such as accessing browsing data that's been cached in memory.
In short, "privacy" mode can be anything but, at least against a determined adversary or forensic investigator.
Then again, what draws people to use privacy mode? To find out, the researchers also spent $120 to purchase 155,216 impressions for two advertising campaigns they created, running simultaneously online, then used code in the advertisements to detect whether someone was in private browsing mode. "We found that private browsing was more popular at adult web sites than at gift shopping sites and news sites, which shared a roughly equal level of private browsing use," according to their study.