To clarify, by "simple", I meant that the bug was discoverable, exploitable, and testable by Google's own public interface -- i.e. didn't require the researcher

To clarify, by "simple", I meant that the bug was discoverable, exploitable, and testable by Google's own public interface -- i.e. didn't require the researcher to break into anything, or find an otherwise extreme set of conditions. This isn't meant to impugn the skill of the researcher, just to point out how amazing it was that such a bug could exist in the open. I wonder if any analysis was done to figure out how many customers (good and bad) specified cross-domain redirects for sitemaps. Should have been easy to calculate, I assume.