This means that an attacker would have a user's Google.com domain cookie, which is the single sign-On cookie to all Google services.
However rather than publish the vulnerability, Inferno reported it straight to Google, which responded within the hour and fixed the flaw after a little more than two weeks.
Inferno said on the blog: "I believe in responsible disclosure, so I waited for this vulnerability to be fixed completely."
Inferno said that the time Google took to fix the flaw was due to vulnerable python script being used in lots of places.
A Google spokesperson said: "We immediately investigated this issue after it was privately reported to us, and we resolved it prior to publication. We take the security of our users very seriously."
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