Opera scrambles to quash zero-day bug in freshly-patched browser

Just a few days after Opera Software patched critical vulnerabilities in its browser, researchers have identified another serious bug that allows attackers to remotely execute malicious code on the machines of people running the most recent version of the software. Opera has vowed to fix the flaw soon.

Among the bugs squashed in Opera 9.61 was a stored cross site scripting (XSS) vulnerability that allowed attackers to view victims' browsing history. That attack is no longer possible, but now researchers have discovered an even more serious exploit that's based on the same weakness.

Simply viewing a booby-trapped webpage with Opera is all that's required to run code of an attacker's choosing on a machine. Researcher Aviv Raff shared a link with us that caused our Windows machine to load the calculator, but certainly less benign exploits are possible as well. The attack works on OS X and Linux machines as well, he says.

Opera is aware of the vulnerability and is in the final stages of testing a new version of the browser that fixes the problem, company spokesman Thomas Ford says. He says version 9.62 will be released "very, very soon," but he can't say exactly when.

"We always appreciate people digging and looking for security vulnerabilities in our products," Ford says. "We want them to be as robust as they can be."

The vulnerability was jointly discovered when researchers Roberto Suggi, Stefano Di Paola, and Raff began discussing the possibility of expanding Opera's browser history flaw to carry out other types of mischief. In short order, Raff came up with this proof-of-concept attack that launches a PC's calculator. That exploit no longer works with version 9.61, but a separate exploit, which Raff does not want published, does exactly the same thing on fully patched machines running Opera.

"They should have looked at the code of this local resource for more vulnerabilities," Raff tells El Reg. "The fixed one is within the displayed links in the searched history. The unfixed one is within the Previous/Next links of the history search page itself."

The Opera bug comes as researchers have warned of a separate vulnerability affecting multiple browsers. Exploiting the FTP client XSS design vulnerability could allow attackers to "execute arbitrary script code in the browser of an unsuspecting user in the context of an FTP session," Sunbelt Software's Michael St. Neitzel warns here. Firefox and Google Chrome are both vulnerable. ®