Password-stealing flaws in LastPass Chrome and Firefox extensions

Critical vulnerabilities in the Chrome and Firefox extensions for LastPass could be exploited to steal passwords and remotely execute code.

woman on tablet with broken lock

Tavis Ormandy, a security researcher on Google’s Project Zero team, warned of flaws in LastPass browser extensions, vulnerabilities which – if a person surfed to a malicious site – would allow the malicious site to steal passwords from the password manager.

LastPass said it patched the vulnerability in its Chrome extension and said it is working on a fix for the flaw in its Firefox add-on.

Ormandy originally said the LastPass bug affected 4.1.42 Chrome and Firefox browser extensions. He developed a working exploit for a Windows box running the LastPass Chrome extension, but said it “could be made to work on other platforms.” He sent the details to LastPass before adding:

Full exploit is two lines of javascript. #sigh ¯\_(ツ)_/¯

“There are a lot of RPCs [Remote Procedure Calls], allowing complete control of the LastPass extension, including stealing passwords,” Ormandy wrote. His bug report explained that there are hundreds of internal privileged LastPass RPC commands, but LastPass users wouldn’t want bad actors accessing RPCs which would allow passwords to be copied.

If “Binary Component” is installed – it is on by default in Firefox and Internet Explorer – then Ormandy said, “This even allows arbitrary code execution.” In case you don’t know, remote code execution (RCE) is a critical vulnerability and as bad as a flaw gets; you could think of it like the devil – unless of course you are a bad guy wanting to remotely control your target’s computer and then it would be your friend.

If you are running a vulnerable LastPass browser extension version, then Ormandy’s proof-of-concept demonstration will run Windows Calculator. It doesn’t seem like rocket science to grasp that Windows Calculator will only run on Windows. Nevertheless, in the bug report, Ormandy said LastPass initially told him that “they couldn't get my exploit to work, but I checked my Apache access logs and they were using a Mac. Naturally, calc.exe will not appear on a Mac.”

LastPass first came up with a workaround, but a few hours later declared the security issue was fixed. Details were to be published on the company’s blog, but were not published at the time of writing this.

Ormandy didn’t reveal details until LastPass said the RCE vulnerability in the Chrome extension had been addressed. He hoped LastPass had resolved the issue instead of just removing the DNS entry, or else DNS responses could be inserted during a man-in-the-middle attack.

A few hours later, Ormandy tweeted:

I found another bug in LastPass 4.1.35 (unpatched), allows stealing passwords for any domain. Full report will be on the way shortly.

A few hours after that, LastPass tweeted, “We are aware of reports of a Firefox add-on vulnerability. Our security is investigating and working on issuing a fix.”

About two weeks ago, LastPass said it planned to retire the LastPass 3.3.2 Firefox add-on due to Mozilla’s plans to move from its add-on API to WebExtensions by the end of 2017. 3.3.2 is the most popular LastPass add-on for Firefox, but it was to be replaced by the add-on version 4.x in April.

This is not the first time security researchers, including Ormandy, have taken aim at LastPass. If you are sticking with LastPass, please make sure you have the most updated version of the software. Some people advise dumping it for a different password manager, while other experts say using any password manager is better than using none and reusing the same old pathetic password on multiple sites.

Copyright © 2017 IDG Communications, Inc.

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