This is yet another reason why sanitizing OpenAuth or other token urls to the minimal allowed to resolve (the hostname) is good practice.
So exactly what is the issue at hand?
Well LastPass as with most password managers that in some way connect to a sync or cloud mechanism, uses a cookie of sorts on all sites you setup with autofill ( no typing needed, great defense against keyloggers), however the issue is that the parser to determine if such a site is accessed / logged in leaves cleartext tokens in the url and takes a malformed url as username:password @ foo.tld i.e. firstname.lastname@example.org which allows an attacker on a machine that is logged in (without 2fa –more on this later) to spill the beans about all passwords in 2 ways.
Method 1: log in or access a machine that is logged in and not locked out (Lock screens are useful folks) to access without any further password/credential prompts the password store and click ‘show password’ and then jig is up. As alluded to earlier if 2fa (two factor auth) is enabled this is thwarted as it requires that secondary challenge for anything account or password store related.
Method 2: Typing in the username (in plaintext in password store) and the target site and the password becomes visible in plaintext in the url.
The really scary part is that now 2 security researchers have exposed these attacks and its still unpatched.
Original article courtesy of https://www.thehackernews.com