Google this week patched several vulnerabilities in Chrome, including two a French security company said could be used to bypass the browser's anti-exploit technology.
But Chrome 11.0.696.71, which Google rolled out yesterday to users via its automatic update mechanism, does not patch the flaw that Vupen researchers said earlier this month could be exploited on Windows 7.
Tuesday's security update was the second for the Chrome "stable" build -- the most polished version of the browser -- this month.
Google fixed four vulnerabilities in the update, including two rated "critical," the category typically reserved for bugs that may let an attacker escape Chrome's "sandbox." Google has patched five critical bugs so far this year.
One of the remaining pair of flaws was ranked "high" -- and got the researcher who reported it a $1,000 bug bounty -- while the other was labeled "low" on Google's four-step threat scoring system.
The two critical vulnerabilities were credited to Google's own security engineers.
Although Google declined to confirm that the two most serious bugs could be used by attackers to break out of the Chrome sandbox, and thus plant malicious code on the computer, French security firm Vupen said that that was likely.
"The vulnerabilities fixed today and related to GPU and blob handling are a typical example of critical vulnerabilities that can affect Chrome and can be exploited to execute arbitrary code outside the sandbox," said Chaouki Bekar, Vupen's CEO and head of research, in an email reply to questions.
Still unpatched, said Bekar, is the bug or bugs that Vupen said its researchers found, then figured out how to exploit, earlier this month.
"The recent flaws we discovered in Chrome, including the sandbox bypass, remain unpatched and our exploit code works with version 11.0.696.71, too," said Bekar.
Those vulnerabilities made news earlier this month when Vupen announced it had hacked Chrome by sidestepping not only the browser's built-in sandbox but also by evading Windows 7's integrated anti-exploit technologies.
Within days, several Google engineers denied that the bugs Vupen exploited were in Chrome itself, claiming instead that the French firm leveraged a flaw in Adobe's Flash, which Google bundles with Chrome.
Chrome has been resistant to attack, primarily because of its sandbox technology, which is designed to isolate the browser from the rest of the machine, making it very difficult for a hacker to execute code on the computer.
For example, Chrome has escaped unscathed in each of the last three Pwn2Own hacking contests, an annual challenge hosted by the CanSecWest conference in Vancouver, British Columbia, and sponsored by HP TippingPoint's bug bounty program. No other browser included in Pwn2Own has matched Chrome's record at the contest.
On Tuesday, Google spokesman Jay Nancarrow declined to comment further about the Vupen exploit claims, and referred to previous statements that Google was unable to investigate the bugs because Vupen would not share details of the flaws.
Last year, Vupen announced a change in its vulnerability disclosure policies, saying it would no longer report bugs to vendors -- as do many researchers -- but would reveal its work only to paying customers.
According to Web measurement company Net Applications, Chrome accounted for 11.9% of all browsers used last month, putting Google's program in third place behind Microsoft's Internet Explorer, with 55.1%, and Mozilla's Firefox, with 21.6%.
Chrome 11 can be downloaded for Windows, Mac OS X and Linux from Google's Web site. Users already running the browser will be updated automatically.