Joseph, I don't expect it's actually the image loading that does anything. I took a quick scan of the source when the problem was visible, and it was evident that two things were happening:
1) Stuff was being loaded from a personal location on somewhere.google.com, where "somewhere" appeared to be a personal system/domain, named after the original poster. 2) JavaScript code was being loaded. My strong suspicion is that the original poster simply created a JavaScript script in somewhere.google.com, and this JavaScript deleted the cookie. This would work if the session cookie is restricted to google.com, which would let any web server in, or content served from the google.com domain (or any subdomain). My note about using NoScript to restrict JavaScript execution to mail.google.com reinforces this suspicion. If my suspicion is correct, then google did two things. First, google appears to allow individuals to create personal domain names in google.com, and to place arbitrary content in those domains. This first thing probalby allowed the original poster to place the JavaScript in a location where it could access the google.com cookie. Second, google apparantly did not restrict the gmail cookie to mail.google.com. This second thing allowed the JavaScript from the personal system at somewhere.google.com to access the cookie. Of course, I only did a cursory glance at the source of the webpage, so I may be wrong :) But, we can be reasonably sure it's not exploiting a problem in the browser, since the issue appears to be cross browser. -- Aaron On 12/8/07, Joseph Hick <[EMAIL PROTECTED]> wrote: > could someone please explain how this PoC works? I wonder why simply loading > an image logs me out > > Kristian Erik Hermansen <[EMAIL PROTECTED]> wrote: > On Dec 7, 2007 7:40 AM, Aaron Katz wrote: > > Could you please explain the vulnerability? When I test, and I submit > > a correct response to the CAPTCHA, I'm presented with knowledge based > > authentication. > > The bug, unless Google fixed it already, will have an affect on your > GMail account, but has nothing to do with CAPTCHAs. Here is an > illustration.... > > * You are happily browsing some emails in GMail. > * You then visit any website which utilizes my PoC. (one @ > http://www.kristian-hermansen.com) > * You try to use your GMail account, but something went wrong. > * You ask yourself what happened... > -- > Kristian Erik Hermansen > "I have no special talent. I am only passionately curious." > > _______________________________________________ > Full-Disclosure - We believe in it. > Charter: > http://lists.grok.org.uk/full-disclosure-charter.html > Hosted and sponsored by Secunia - http://secunia.com/ > > > > ________________________________ > Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it > now. > > _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
