Distributed storage systems are upgraded constantly, and one subtle class of bug — data format incompatibility, where a new version misreads data written by the old one — ranks among the leading causes of cloud incidents during upgrades, with consequences as severe as data loss and cluster-wide outages. UpFuzz, an award-winning open-source fuzzer from Purdue University, is the first tool built specifically to hunt these cross-version bugs. It has already uncovered 15 previously unknown failures in the latest stable releases of Cassandra, HBase, and HDFS — and its evaluation was run on bare metal testbed infrastructure that included Chameleon.