LastPass has fixed a security bug that potentially allowed malicious websites to obtain the username and passphrase inserted by the password manager on the previously visited site.
In other words, if you visited website A, and LastPass automatically injected a username and password for you to log in, and then you surfed to website B, the latter could access the password issued to website A. Netizens are advised to update LastPass to version 4.33.0 or later, which squashes this bug. The password manager's Chrome and Opera extensions were vulnerable, specifically.
Google Project Zero flaw-finder Tavis Ormandy discovered and privately reported the programming blunder, which is technically a clickjacking vulnerability, and went public with the details on Sunday night.
"To exploit this bug, a series of actions would need to be taken by a LastPass user including filling a password with the LastPass icon, then visiting a compromised or malicious site and finally being tricked into clicking on the page several times," LastPass explained just before the weekend.
"This exploit may result in the last site credentials filled by LastPass to be exposed."
According to Ormandy, a malicious page would be able exploit the flaw, and steal login information for the previous site, by creating popup windows and accessing cached credentials.
"I noticed that you can create a popup without calling do_popupregister() by iframing popupfilltab.html (i.e. via moz-extension, ms-browser-extension, chrome-extension, etc). It's a valid web_accessible_resource," Ormandy explained in his now-public bug report.
"Because do_popupregister() is never called, ftd_get_frameparenturl() just uses the last cached value in g_popup_url_by_tabid for the current tab. That means via some clickjacking, you can leak the credentials for the previous site logged in for the current tab."
In practice, an attacker would be able to lure users to malicious pages that would be able to abuse the bug to harvest credentials in some cases. There are no public reports of this actually happening, however, as Ormandy privately tipped off LastPass, which got a patch out before the flaw was publicly disclosed.
Again, users and admins are advised to make sure they have updated to the latest version of LastPass (4.33.0 or later) to make sure the vulnerability is patched. ®