LastPass, the world most popular password vault, has issued a fix to an information disclosure flaw discovered by Google’s Project Zero.

Google’s Project Zero security research team discovered a flaw in the LastPass plugins for the Chrome and Opera browsers.  By exploiting the flaw, an attacker could obtain a copy of the last credentials the password manager had entered on a website in the same browser tab.  The flaw was reported to LastPass under Project Zero’s disclosure rules and a fix was issued by LastPass before the public release of the details of the vulnerability.

The javascript based exploit calls the LastPass popupfilltab.html within an iframe rather than via the expected do_popupregister() and as a result the plugin is tricked into populating the form with the last used credentials from the previous site visited in the same tab.

The issue, which only affected the Chrome and Opera browser extensions, is fixed in LastPass version 4.33.0 issued on September 13^th2019.  LastPass stated in their bug report that although the exploit only worked on Chrome and Opera, they have pushed the fix to all browser versions as a precaution.

The approach taken by LastPass to update all their extensions, not just the ones affected by the flaw, provide a good example for security minded programmers to follow. It is easy to forget that the environment that code runs in is always changing – as other components as patched and updated.  This raises the potential risk that a flaw in the code which is not exploitable today (because of external factors) could become suddenly exploitable in the future when those external factors change.

LastPass offers the following best practice advice for online-safety:

• Beware of phishing attacks. Do not click on links from people you don’t know, or that seem out of character from your trusted contacts and companies.

• Always enable MFA for LastPass and other services like your bank, email, Twitter, Facebook, etc. Adding additional layers of authentication remains the most effective way to protect your account.

• Never reuse your LastPass master password and never disclose it to anyone, including us.

• Use different, unique passwords for every online account.

• Keep your computer malware-free by running antivirus with the latest detection patterns and keeping your software up-to-date.

Despite the risks posed by vulnerabilities like this, the overall benefits of password managers will out-weigh the risks for most users.  The ability of password managers to: generate secure passwords for every site, guarantee that passwords are not re-used across systems and even allow credentials to be shared between password vaults without allowing the humans involved to see the passwords themselves with improve the security stance of most organisations.