Popular password manager LastPass said it fixed two vulnerabilities that were found last year. The disclosure comes just ahead of a security conference where a research paper describing the problems is due to be presented.
Zhiwei Li, a research scientist at Shape Security, reported the flaws to LastPass in August 2013, which were "addressed immediately," LastPass wrote on its blog.
Both flaws involved "bookmarklets," which assist in filling out stored password information when LastPass's plugin can't be used, such as when using a mobile browser.
One flaw could be exploited if a bookmarklet was used on a website rigged to attack it, LastPass wrote. The other vulnerability could allow an attacker to create a bogus one-time password (OTP) if a LastPass user was tricked into visiting a malicious website.
The OTP attack would require a hacker to know a person's username in order to exploit it and also serve a custom attack, LastPass wrote.
"Even if this was exploited, the attacker would still not have the key to decrypt user data," the company said.
Zhiwei co-authored a research paper that has been accepted by the Usenix Security Symposium, which starts in San Diego on Aug. 20.
The study analyzed five popular Web-based password managers: LastPass, RoboForm, My1login, PasswordBox and NeedMyPassword, all of which run in a Web browser.
The researchers wrote that "in four out of the five password managers we studied, an attacker can learn a user's credentials for arbitrary websites."
LastPass wrote it didn't believe anyone other than Zhiwei exploited the flaws. Still, "if you are concerned that you've used bookmarklets before September 2013 on non-trustworthy sites, you may consider changing your master password and generating new passwords, though we don't think it is necessary."
Send news tips and comments to email@example.com. Follow me on Twitter: @jeremy_kirk