A vulnerability in Firefox's popup blocker software creates a means to read files from affected systems, security researchers warn. The flaw, coupled with some tricksy coding, establishes a mechanism for hackers to read user-accessible files on vulnerable system, thereby creating a means to swipe sensitive information. Firefox version 18.104.22.168 is known to be exposed to the exploit. Other versions of the popular web surfing package might also be affected.
The vulnerability was discovered by security researcher Michal Zalewski who said the exploit relies in part on the fact that normal URL permission checks, which would stop remote sites from accessing a user's filespace, are bypassed when a user chooses to manually allow a blocked popup.