The bug lay in the m.google.com domain used by Google Buzz for mobile, and could have been exploited by hackers to manipulate other people's Google Buzz accounts.
This type of flaw, known as a cross-site scripting error, is common, but it can have nasty consequences on widely used sites such as Google.
In addition to taking control of Buzz accounts, scammers could have leveraged the flaw to create hard-to-detect phishing pages that used the Google.com web domain.
Google spokesman Jay Nancarrow said that the company has "no indication that the vulnerability was actively abused".
Launched just last week, Google Buzz has had a rough rollout.
Over the weekend, Google was forced to make changes to the service after users complained that it exposed potentially private information by automatically publishing lists of users' closest Gmail contacts.
See also: Google Buzz attracting spammers already