Mozilla marked Bug ID 413250 as ‘RESOLVED FIXED’ on Tuesday. I got a chance to check out the fix today, and found that the fix is inadequate in stopping the attack. Here’s another demo that reads your session store, and like before, uses the Download Statusbar extension.
steal_sessionstore2.html.
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I spent some time tonight with scripting access to chrome files and found that Firefox doesn’t properly handle escaped characters. Its possible to load any javascript file on a victims machine. This attack is similar to previously disclosed vulnerabilities but is not constrained to basic Firefox files.
To exploit this the victim needs to have an extension installed that does not store its contents in a jar archive (such as the Download Statusbar). I created a demo that will read the Mozilla Thunderbird preferences file all.js (C:\Program Files\Mozilla Thunderbird\greprefs\all.js).
This looks very interesting and may have bigger potential, but for now, its just another information disclosure.
UPDATE:
There seems to be some confusion about what exactly the severity of this vulnerability is. First, this is not a chrome privilege escalation but it worse than just leaking some variables. I created another demo to read the sessionstore.js file. This will display information regarding your current session (windows, tabs, cookies, etc).
The demo’s use Download Statusbar but any ‘flat’ extension (not contained in a JAR file) will work (including greasemonkey). If you want to track this bug, the mozilla bug id is 413250 .
If you are using Firefox you need to have NoScript, it has stopped this type of attack since August 2007!
UPDATE 2:
Mozilla has marked this as a high severity bug and released a partial list of affected plugins here: https://bugzilla.mozilla.org/attachment.cgi?id=300181
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