Cache poisoning via missing digest verification

Integrity bypass in Uber Kraken 0.1.27 and earlier allows remote attackers to poison cached blobs via forged peer-to-peer piece data. In the agent P2P download path, Torrent.writePiece accepts each received piece after only a CRC32 check, and WritePiece then commits the assembled blob into the content-addressable cache under the requested SHA-256 digest without recomputing that digest. Exploitation requires a malicious peer or an attacker on agent-to-agent traffic; later hosts that pull the poisoned layer or manifest can execute attacker-chosen container content.